Date: 2026-03-01T05:25:06+00:00

Actual source code: snes.c

      1: #include <petsc/private/snesimpl.h>
      2: #include <petscdmshell.h>
      3: #include <petscdraw.h>
      4: #include <petscds.h>
      5: #include <petscdmadaptor.h>
      6: #include <petscconvest.h>

      8: PetscBool         SNESRegisterAllCalled = PETSC_FALSE;
      9: PetscFunctionList SNESList              = NULL;

     11: /* Logging support */
     12: PetscClassId  SNES_CLASSID, DMSNES_CLASSID;
     13: PetscLogEvent SNES_Solve, SNES_SetUp, SNES_FunctionEval, SNES_JacobianEval, SNES_NGSEval, SNES_NGSFuncEval, SNES_NewtonALEval, SNES_NPCSolve, SNES_ObjectiveEval;

     15: /*@
     16:   SNESSetErrorIfNotConverged - Causes `SNESSolve()` to generate an error immediately if the solver has not converged.

     18:   Logically Collective

     20:   Input Parameters:
     21: + snes - iterative context obtained from `SNESCreate()`
     22: - flg  - `PETSC_TRUE` indicates you want the error generated

     24:   Options Database Key:
     25: . -snes_error_if_not_converged <true,false> - cause an immediate error condition and stop the program if the solver does not converge

     27:   Level: intermediate

     29:   Note:
     30:   Normally PETSc continues if a solver fails to converge, you can call `SNESGetConvergedReason()` after a `SNESSolve()`
     31:   to determine if it has converged. Otherwise the solution may be inaccurate or wrong

     33: .seealso: [](ch_snes), `SNES`, `SNESGetErrorIfNotConverged()`, `KSPGetErrorIfNotConverged()`, `KSPSetErrorIfNotConverged()`
     34: @*/
     35: PetscErrorCode SNESSetErrorIfNotConverged(SNES snes, PetscBool flg)
     36: {
     37:   PetscFunctionBegin;
     40:   snes->errorifnotconverged = flg;
     41:   PetscFunctionReturn(PETSC_SUCCESS);
     42: }

     44: /*@
     45:   SNESGetErrorIfNotConverged - Indicates if `SNESSolve()` will generate an error if the solver does not converge?

     47:   Not Collective

     49:   Input Parameter:
     50: . snes - iterative context obtained from `SNESCreate()`

     52:   Output Parameter:
     53: . flag - `PETSC_TRUE` if it will generate an error, else `PETSC_FALSE`

     55:   Level: intermediate

     57: .seealso: [](ch_snes), `SNES`, `SNESSolve()`, `SNESSetErrorIfNotConverged()`, `KSPGetErrorIfNotConverged()`, `KSPSetErrorIfNotConverged()`
     58: @*/
     59: PetscErrorCode SNESGetErrorIfNotConverged(SNES snes, PetscBool *flag)
     60: {
     61:   PetscFunctionBegin;
     63:   PetscAssertPointer(flag, 2);
     64:   *flag = snes->errorifnotconverged;
     65:   PetscFunctionReturn(PETSC_SUCCESS);
     66: }

     68: /*@
     69:   SNESSetAlwaysComputesFinalResidual - tells the `SNES` to always compute the residual (nonlinear function value) at the final solution

     71:   Logically Collective

     73:   Input Parameters:
     74: + snes - the shell `SNES`
     75: - flg  - `PETSC_TRUE` to always compute the residual

     77:   Level: advanced

     79:   Note:
     80:   Some solvers (such as smoothers in a `SNESFAS`) do not need the residual computed at the final solution so skip computing it
     81:   to save time.

     83: .seealso: [](ch_snes), `SNES`, `SNESFAS`, `SNESSolve()`, `SNESGetAlwaysComputesFinalResidual()`
     84: @*/
     85: PetscErrorCode SNESSetAlwaysComputesFinalResidual(SNES snes, PetscBool flg)
     86: {
     87:   PetscFunctionBegin;
     89:   snes->alwayscomputesfinalresidual = flg;
     90:   PetscFunctionReturn(PETSC_SUCCESS);
     91: }

     93: /*@
     94:   SNESGetAlwaysComputesFinalResidual - checks if the `SNES` always computes the residual at the final solution

     96:   Logically Collective

     98:   Input Parameter:
     99: . snes - the `SNES` context

    101:   Output Parameter:
    102: . flg - `PETSC_TRUE` if the residual is computed

    104:   Level: advanced

    106: .seealso: [](ch_snes), `SNES`, `SNESFAS`, `SNESSolve()`, `SNESSetAlwaysComputesFinalResidual()`
    107: @*/
    108: PetscErrorCode SNESGetAlwaysComputesFinalResidual(SNES snes, PetscBool *flg)
    109: {
    110:   PetscFunctionBegin;
    112:   *flg = snes->alwayscomputesfinalresidual;
    113:   PetscFunctionReturn(PETSC_SUCCESS);
    114: }

    116: /*@
    117:   SNESSetFunctionDomainError - tells `SNES` that the input vector, a proposed new solution, to your function you provided to `SNESSetFunction()` is not
    118:   in the functions domain. For example, a step with negative pressure.

    120:   Not Collective

    122:   Input Parameter:
    123: . snes - the `SNES` context

    125:   Level: advanced

    127:   Notes:
    128:   This does not need to be called by all processes in the `SNES` MPI communicator.

    130:   If this is called the `SNESSolve()` stops iterating and returns with a `SNESConvergedReason` of `SNES_DIVERGED_FUNCTION_DOMAIN`

    132:   You should always call `SNESGetConvergedReason()` after each `SNESSolve()` and verify if the iteration converged (positive result) or diverged (negative result).

    134:   You can direct `SNES` to avoid certain steps by using `SNESVISetVariableBounds()`, `SNESVISetComputeVariableBounds()` or
    135:   `SNESLineSearchSetPreCheck()`, `SNESLineSearchSetPostCheck()`

    137:   You can call `SNESSetJacobianDomainError()` during a Jacobian computation to indicate the proposed solution is not in the domain.

    139:   Developer Note:
    140:   This value is used by `SNESCheckFunctionNorm()` to determine if the `SNESConvergedReason` is set to `SNES_DIVERGED_FUNCTION_DOMAIN`

    142: .seealso: [](ch_snes), `SNESCreate()`, `SNESSetFunction()`, `SNESFunctionFn`, `SNESSetJacobianDomainError()`, `SNESVISetVariableBounds()`,
    143:           `SNESVISetComputeVariableBounds()`, `SNESLineSearchSetPreCheck()`, `SNESLineSearchSetPostCheck()`, `SNESConvergedReason`, `SNESGetConvergedReason()`,
    144:           `SNES_DIVERGED_FUNCTION_DOMAIN`
    145: @*/
    146: PetscErrorCode SNESSetFunctionDomainError(SNES snes)
    147: {
    148:   PetscFunctionBegin;
    150:   snes->domainerror = PETSC_TRUE;
    151:   PetscFunctionReturn(PETSC_SUCCESS);
    152: }

    154: /*@
    155:   SNESSetJacobianDomainError - tells `SNES` that the function you provided to `SNESSetJacobian()` at the proposed step. For example there is a negative element transformation.

    157:   Logically Collective

    159:   Input Parameter:
    160: . snes - the `SNES` context

    162:   Level: advanced

    164:   Notes:
    165:   If this is called the `SNESSolve()` stops iterating and returns with a `SNESConvergedReason` of `SNES_DIVERGED_FUNCTION_DOMAIN`

    167:   You should always call `SNESGetConvergedReason()` after each `SNESSolve()` and verify if the iteration converged (positive result) or diverged (negative result).

    169:   You can direct `SNES` to avoid certain steps by using `SNESVISetVariableBounds()`, `SNESVISetComputeVariableBounds()` or
    170:   `SNESLineSearchSetPreCheck()`, `SNESLineSearchSetPostCheck()`

    172: .seealso: [](ch_snes), `SNESCreate()`, `SNESSetFunction()`, `SNESFunctionFn`, `SNESSetFunctionDomainError()`, `SNESVISetVariableBounds()`,
    173:           `SNESVISetComputeVariableBounds()`, `SNESLineSearchSetPreCheck()`, `SNESLineSearchSetPostCheck()`, `SNESConvergedReason`, `SNESGetConvergedReason()`
    174: @*/
    175: PetscErrorCode SNESSetJacobianDomainError(SNES snes)
    176: {
    177:   PetscFunctionBegin;
    179:   PetscCheck(!snes->errorifnotconverged, PETSC_COMM_SELF, PETSC_ERR_ARG_OUTOFRANGE, "User code indicates computeJacobian does not make sense");
    180:   snes->jacobiandomainerror = PETSC_TRUE;
    181:   PetscFunctionReturn(PETSC_SUCCESS);
    182: }

    184: /*@
    185:   SNESSetCheckJacobianDomainError - tells `SNESSolve()` whether to check if the user called `SNESSetJacobianDomainError()` Jacobian domain error after
    186:   each Jacobian evaluation. By default, it checks for the Jacobian domain error in the debug mode, and does not check it in the optimized mode.

    188:   Logically Collective

    190:   Input Parameters:
    191: + snes - the `SNES` context
    192: - flg  - indicates if or not to check Jacobian domain error after each Jacobian evaluation

    194:   Level: advanced

    196:   Note:
    197:   Checks require one extra parallel synchronization for each Jacobian evaluation

    199: .seealso: [](ch_snes), `SNES`, `SNESConvergedReason`, `SNESCreate()`, `SNESSetFunction()`, `SNESFunctionFn`, `SNESSetFunctionDomainError()`, `SNESGetCheckJacobianDomainError()`
    200: @*/
    201: PetscErrorCode SNESSetCheckJacobianDomainError(SNES snes, PetscBool flg)
    202: {
    203:   PetscFunctionBegin;
    205:   snes->checkjacdomainerror = flg;
    206:   PetscFunctionReturn(PETSC_SUCCESS);
    207: }

    209: /*@
    210:   SNESGetCheckJacobianDomainError - Get an indicator whether or not `SNES` is checking Jacobian domain errors after each Jacobian evaluation.

    212:   Logically Collective

    214:   Input Parameter:
    215: . snes - the `SNES` context

    217:   Output Parameter:
    218: . flg - `PETSC_FALSE` indicates that it is not checking Jacobian domain errors after each Jacobian evaluation

    220:   Level: advanced

    222: .seealso: [](ch_snes), `SNES`, `SNESCreate()`, `SNESSetFunction()`, `SNESFunctionFn`, `SNESSetFunctionDomainError()`, `SNESSetCheckJacobianDomainError()`
    223: @*/
    224: PetscErrorCode SNESGetCheckJacobianDomainError(SNES snes, PetscBool *flg)
    225: {
    226:   PetscFunctionBegin;
    228:   PetscAssertPointer(flg, 2);
    229:   *flg = snes->checkjacdomainerror;
    230:   PetscFunctionReturn(PETSC_SUCCESS);
    231: }

    233: /*@
    234:   SNESGetFunctionDomainError - Gets the status of the domain error after a call to `SNESComputeFunction()`

    236:   Not Collective, different MPI processes may return different values

    238:   Input Parameter:
    239: . snes - the `SNES` context

    241:   Output Parameter:
    242: . domainerror - Set to `PETSC_TRUE` if there's a domain error; `PETSC_FALSE` otherwise.

    244:   Level: developer

    246:   Notes:
    247:   The value will only be true on those MPI processes that called `SNESSetFunctionDomainError()`

    249:   The value is reset to `PETSC_FALSE` when `SNESCheckFunctionNorm()` is called.

    251: .seealso: [](ch_snes), `SNES`, `SNESSetFunctionDomainError()`, `SNESComputeFunction()`
    252: @*/
    253: PetscErrorCode SNESGetFunctionDomainError(SNES snes, PetscBool *domainerror)
    254: {
    255:   PetscFunctionBegin;
    257:   PetscAssertPointer(domainerror, 2);
    258:   *domainerror = snes->domainerror;
    259:   PetscFunctionReturn(PETSC_SUCCESS);
    260: }

    262: /*@
    263:   SNESGetJacobianDomainError - Gets the status of the Jacobian domain error after a call to `SNESComputeJacobian()`

    265:   Not Collective, different MPI processes may return different values

    267:   Input Parameter:
    268: . snes - the `SNES` context

    270:   Output Parameter:
    271: . domainerror - Set to `PETSC_TRUE` if there's a Jacobian domain error; `PETSC_FALSE` otherwise.

    273:   Level: advanced

    275:   Notes:
    276:   The value will only be true on those MPI processes that called `SNESSetJacobianDomainError()`

    278:   The value is reset to `PETSC_FALSE` when `SNESCheckJacobianDomainerror()` is called but only `SNESSetCheckJacobianDomainError()` was called

    280: .seealso: [](ch_snes), `SNES`, `SNESSetFunctionDomainError()`, `SNESComputeFunction()`, `SNESGetFunctionDomainError()`
    281: @*/
    282: PetscErrorCode SNESGetJacobianDomainError(SNES snes, PetscBool *domainerror)
    283: {
    284:   PetscFunctionBegin;
    286:   PetscAssertPointer(domainerror, 2);
    287:   *domainerror = snes->jacobiandomainerror;
    288:   PetscFunctionReturn(PETSC_SUCCESS);
    289: }

    291: /*@
    292:   SNESLoad - Loads a `SNES` that has been stored in `PETSCVIEWERBINARY` with `SNESView()`.

    294:   Collective

    296:   Input Parameters:
    297: + snes   - the newly loaded `SNES`, this needs to have been created with `SNESCreate()` or
    298:            some related function before a call to `SNESLoad()`.
    299: - viewer - binary file viewer, obtained from `PetscViewerBinaryOpen()`

    301:   Level: intermediate

    303:   Note:
    304:   The `SNESType` is determined by the data in the file, any type set into the `SNES` before this call is ignored.

    306: .seealso: [](ch_snes), `SNES`, `PetscViewer`, `SNESCreate()`, `SNESType`, `PetscViewerBinaryOpen()`, `SNESView()`, `MatLoad()`, `VecLoad()`
    307: @*/
    308: PetscErrorCode SNESLoad(SNES snes, PetscViewer viewer)
    309: {
    310:   PetscBool isbinary;
    311:   PetscInt  classid;
    312:   char      type[256];
    313:   KSP       ksp;
    314:   DM        dm;
    315:   DMSNES    dmsnes;

    317:   PetscFunctionBegin;
    320:   PetscCall(PetscObjectTypeCompare((PetscObject)viewer, PETSCVIEWERBINARY, &isbinary));
    321:   PetscCheck(isbinary, PETSC_COMM_SELF, PETSC_ERR_ARG_WRONG, "Invalid viewer; open viewer with PetscViewerBinaryOpen()");

    323:   PetscCall(PetscViewerBinaryRead(viewer, &classid, 1, NULL, PETSC_INT));
    324:   PetscCheck(classid == SNES_FILE_CLASSID, PetscObjectComm((PetscObject)snes), PETSC_ERR_ARG_WRONG, "Not SNES next in file");
    325:   PetscCall(PetscViewerBinaryRead(viewer, type, 256, NULL, PETSC_CHAR));
    326:   PetscCall(SNESSetType(snes, type));
    327:   PetscTryTypeMethod(snes, load, viewer);
    328:   PetscCall(SNESGetDM(snes, &dm));
    329:   PetscCall(DMGetDMSNES(dm, &dmsnes));
    330:   PetscCall(DMSNESLoad(dmsnes, viewer));
    331:   PetscCall(SNESGetKSP(snes, &ksp));
    332:   PetscCall(KSPLoad(ksp, viewer));
    333:   PetscFunctionReturn(PETSC_SUCCESS);
    334: }

    336: #include <petscdraw.h>
    337: #if defined(PETSC_HAVE_SAWS)
    338: #include <petscviewersaws.h>
    339: #endif

    341: /*@
    342:   SNESViewFromOptions - View a `SNES` based on values in the options database

    344:   Collective

    346:   Input Parameters:
    347: + A    - the `SNES` context
    348: . obj  - Optional object that provides the options prefix for the checks
    349: - name - command line option

    351:   Level: intermediate

    353: .seealso: [](ch_snes), `SNES`, `SNESView`, `PetscObjectViewFromOptions()`, `SNESCreate()`
    354: @*/
    355: PetscErrorCode SNESViewFromOptions(SNES A, PetscObject obj, const char name[])
    356: {
    357:   PetscFunctionBegin;
    359:   PetscCall(PetscObjectViewFromOptions((PetscObject)A, obj, name));
    360:   PetscFunctionReturn(PETSC_SUCCESS);
    361: }

    363: PETSC_EXTERN PetscErrorCode SNESComputeJacobian_DMDA(SNES, Vec, Mat, Mat, void *);

    365: /*@
    366:   SNESView - Prints or visualizes the `SNES` data structure.

    368:   Collective

    370:   Input Parameters:
    371: + snes   - the `SNES` context
    372: - viewer - the `PetscViewer`

    374:   Options Database Key:
    375: . -snes_view - Calls `SNESView()` at end of `SNESSolve()`

    377:   Level: beginner

    379:   Notes:
    380:   The available visualization contexts include
    381: +     `PETSC_VIEWER_STDOUT_SELF` - standard output (default)
    382: -     `PETSC_VIEWER_STDOUT_WORLD` - synchronized standard
    383:   output where only the first processor opens
    384:   the file.  All other processors send their
    385:   data to the first processor to print.

    387:   The available formats include
    388: +     `PETSC_VIEWER_DEFAULT` - standard output (default)
    389: -     `PETSC_VIEWER_ASCII_INFO_DETAIL` - more verbose output for `SNESNASM`

    391:   The user can open an alternative visualization context with
    392:   `PetscViewerASCIIOpen()` - output to a specified file.

    394:   In the debugger you can do "call `SNESView`(snes,0)" to display the `SNES` solver. (The same holds for any PETSc object viewer).

    396: .seealso: [](ch_snes), `SNES`, `SNESLoad()`, `SNESCreate()`, `PetscViewerASCIIOpen()`
    397: @*/
    398: PetscErrorCode SNESView(SNES snes, PetscViewer viewer)
    399: {
    400:   SNESKSPEW     *kctx;
    401:   KSP            ksp;
    402:   SNESLineSearch linesearch;
    403:   PetscBool      isascii, isstring, isbinary, isdraw;
    404:   DMSNES         dmsnes;
    405: #if defined(PETSC_HAVE_SAWS)
    406:   PetscBool issaws;
    407: #endif

    409:   PetscFunctionBegin;
    411:   if (!viewer) PetscCall(PetscViewerASCIIGetStdout(PetscObjectComm((PetscObject)snes), &viewer));
    413:   PetscCheckSameComm(snes, 1, viewer, 2);

    415:   PetscCall(PetscObjectTypeCompare((PetscObject)viewer, PETSCVIEWERASCII, &isascii));
    416:   PetscCall(PetscObjectTypeCompare((PetscObject)viewer, PETSCVIEWERSTRING, &isstring));
    417:   PetscCall(PetscObjectTypeCompare((PetscObject)viewer, PETSCVIEWERBINARY, &isbinary));
    418:   PetscCall(PetscObjectTypeCompare((PetscObject)viewer, PETSCVIEWERDRAW, &isdraw));
    419: #if defined(PETSC_HAVE_SAWS)
    420:   PetscCall(PetscObjectTypeCompare((PetscObject)viewer, PETSCVIEWERSAWS, &issaws));
    421: #endif
    422:   if (isascii) {
    423:     SNESNormSchedule normschedule;
    424:     DM               dm;
    425:     SNESJacobianFn  *cJ;
    426:     void            *ctx;
    427:     const char      *pre = "";

    429:     PetscCall(PetscObjectPrintClassNamePrefixType((PetscObject)snes, viewer));
    430:     if (!snes->setupcalled) PetscCall(PetscViewerASCIIPrintf(viewer, "  SNES has not been set up so information may be incomplete\n"));
    431:     if (snes->ops->view) {
    432:       PetscCall(PetscViewerASCIIPushTab(viewer));
    433:       PetscUseTypeMethod(snes, view, viewer);
    434:       PetscCall(PetscViewerASCIIPopTab(viewer));
    435:     }
    436:     if (snes->max_funcs == PETSC_UNLIMITED) {
    437:       PetscCall(PetscViewerASCIIPrintf(viewer, "  maximum iterations=%" PetscInt_FMT ", maximum function evaluations=unlimited\n", snes->max_its));
    438:     } else {
    439:       PetscCall(PetscViewerASCIIPrintf(viewer, "  maximum iterations=%" PetscInt_FMT ", maximum function evaluations=%" PetscInt_FMT "\n", snes->max_its, snes->max_funcs));
    440:     }
    441:     PetscCall(PetscViewerASCIIPrintf(viewer, "  tolerances: relative=%g, absolute=%g, solution=%g\n", (double)snes->rtol, (double)snes->abstol, (double)snes->stol));
    442:     if (snes->usesksp) PetscCall(PetscViewerASCIIPrintf(viewer, "  total number of linear solver iterations=%" PetscInt_FMT "\n", snes->linear_its));
    443:     PetscCall(PetscViewerASCIIPrintf(viewer, "  total number of function evaluations=%" PetscInt_FMT "\n", snes->nfuncs));
    444:     PetscCall(SNESGetNormSchedule(snes, &normschedule));
    445:     if (normschedule > 0) PetscCall(PetscViewerASCIIPrintf(viewer, "  norm schedule %s\n", SNESNormSchedules[normschedule]));
    446:     if (snes->gridsequence) PetscCall(PetscViewerASCIIPrintf(viewer, "  total number of grid sequence refinements=%" PetscInt_FMT "\n", snes->gridsequence));
    447:     if (snes->ksp_ewconv) {
    448:       kctx = (SNESKSPEW *)snes->kspconvctx;
    449:       if (kctx) {
    450:         PetscCall(PetscViewerASCIIPrintf(viewer, "  Eisenstat-Walker computation of KSP relative tolerance (version %" PetscInt_FMT ")\n", kctx->version));
    451:         PetscCall(PetscViewerASCIIPrintf(viewer, "    rtol_0=%g, rtol_max=%g, threshold=%g\n", (double)kctx->rtol_0, (double)kctx->rtol_max, (double)kctx->threshold));
    452:         PetscCall(PetscViewerASCIIPrintf(viewer, "    gamma=%g, alpha=%g, alpha2=%g\n", (double)kctx->gamma, (double)kctx->alpha, (double)kctx->alpha2));
    453:       }
    454:     }
    455:     if (snes->lagpreconditioner == -1) {
    456:       PetscCall(PetscViewerASCIIPrintf(viewer, "  Preconditioned is never rebuilt\n"));
    457:     } else if (snes->lagpreconditioner > 1) {
    458:       PetscCall(PetscViewerASCIIPrintf(viewer, "  Preconditioned is rebuilt every %" PetscInt_FMT " new Jacobians\n", snes->lagpreconditioner));
    459:     }
    460:     if (snes->lagjacobian == -1) {
    461:       PetscCall(PetscViewerASCIIPrintf(viewer, "  Jacobian is never rebuilt\n"));
    462:     } else if (snes->lagjacobian > 1) {
    463:       PetscCall(PetscViewerASCIIPrintf(viewer, "  Jacobian is rebuilt every %" PetscInt_FMT " SNES iterations\n", snes->lagjacobian));
    464:     }
    465:     PetscCall(SNESGetDM(snes, &dm));
    466:     PetscCall(DMSNESGetJacobian(dm, &cJ, &ctx));
    467:     if (snes->mf_operator) {
    468:       PetscCall(PetscViewerASCIIPrintf(viewer, "  Jacobian is applied matrix-free with differencing\n"));
    469:       pre = "Preconditioning ";
    470:     }
    471:     if (cJ == SNESComputeJacobianDefault) {
    472:       PetscCall(PetscViewerASCIIPrintf(viewer, "  %sJacobian is built using finite differences one column at a time\n", pre));
    473:     } else if (cJ == SNESComputeJacobianDefaultColor) {
    474:       PetscCall(PetscViewerASCIIPrintf(viewer, "  %sJacobian is built using finite differences with coloring\n", pre));
    475:       /* it slightly breaks data encapsulation for access the DMDA information directly */
    476:     } else if (cJ == SNESComputeJacobian_DMDA) {
    477:       MatFDColoring fdcoloring;
    478:       PetscCall(PetscObjectQuery((PetscObject)dm, "DMDASNES_FDCOLORING", (PetscObject *)&fdcoloring));
    479:       if (fdcoloring) {
    480:         PetscCall(PetscViewerASCIIPrintf(viewer, "  %sJacobian is built using colored finite differences on a DMDA\n", pre));
    481:       } else {
    482:         PetscCall(PetscViewerASCIIPrintf(viewer, "  %sJacobian is built using a DMDA local Jacobian\n", pre));
    483:       }
    484:     } else if (snes->mf && !snes->mf_operator) {
    485:       PetscCall(PetscViewerASCIIPrintf(viewer, "  Jacobian is applied matrix-free with differencing, no explicit Jacobian\n"));
    486:     }
    487:   } else if (isstring) {
    488:     const char *type;
    489:     PetscCall(SNESGetType(snes, &type));
    490:     PetscCall(PetscViewerStringSPrintf(viewer, " SNESType: %-7.7s", type));
    491:     PetscTryTypeMethod(snes, view, viewer);
    492:   } else if (isbinary) {
    493:     PetscInt    classid = SNES_FILE_CLASSID;
    494:     MPI_Comm    comm;
    495:     PetscMPIInt rank;
    496:     char        type[256];

    498:     PetscCall(PetscObjectGetComm((PetscObject)snes, &comm));
    499:     PetscCallMPI(MPI_Comm_rank(comm, &rank));
    500:     if (rank == 0) {
    501:       PetscCall(PetscViewerBinaryWrite(viewer, &classid, 1, PETSC_INT));
    502:       PetscCall(PetscStrncpy(type, ((PetscObject)snes)->type_name, sizeof(type)));
    503:       PetscCall(PetscViewerBinaryWrite(viewer, type, sizeof(type), PETSC_CHAR));
    504:     }
    505:     PetscTryTypeMethod(snes, view, viewer);
    506:   } else if (isdraw) {
    507:     PetscDraw draw;
    508:     char      str[36];
    509:     PetscReal x, y, bottom, h;

    511:     PetscCall(PetscViewerDrawGetDraw(viewer, 0, &draw));
    512:     PetscCall(PetscDrawGetCurrentPoint(draw, &x, &y));
    513:     PetscCall(PetscStrncpy(str, "SNES: ", sizeof(str)));
    514:     PetscCall(PetscStrlcat(str, ((PetscObject)snes)->type_name, sizeof(str)));
    515:     PetscCall(PetscDrawStringBoxed(draw, x, y, PETSC_DRAW_BLUE, PETSC_DRAW_BLACK, str, NULL, &h));
    516:     bottom = y - h;
    517:     PetscCall(PetscDrawPushCurrentPoint(draw, x, bottom));
    518:     PetscTryTypeMethod(snes, view, viewer);
    519: #if defined(PETSC_HAVE_SAWS)
    520:   } else if (issaws) {
    521:     PetscMPIInt rank;
    522:     const char *name;

    524:     PetscCall(PetscObjectGetName((PetscObject)snes, &name));
    525:     PetscCallMPI(MPI_Comm_rank(PETSC_COMM_WORLD, &rank));
    526:     if (!((PetscObject)snes)->amsmem && rank == 0) {
    527:       char dir[1024];

    529:       PetscCall(PetscObjectViewSAWs((PetscObject)snes, viewer));
    530:       PetscCall(PetscSNPrintf(dir, 1024, "/PETSc/Objects/%s/its", name));
    531:       PetscCallSAWs(SAWs_Register, (dir, &snes->iter, 1, SAWs_READ, SAWs_INT));
    532:       if (!snes->conv_hist) PetscCall(SNESSetConvergenceHistory(snes, NULL, NULL, PETSC_DECIDE, PETSC_TRUE));
    533:       PetscCall(PetscSNPrintf(dir, 1024, "/PETSc/Objects/%s/conv_hist", name));
    534:       PetscCallSAWs(SAWs_Register, (dir, snes->conv_hist, 10, SAWs_READ, SAWs_DOUBLE));
    535:     }
    536: #endif
    537:   }
    538:   if (snes->linesearch) {
    539:     PetscCall(SNESGetLineSearch(snes, &linesearch));
    540:     PetscCall(PetscViewerASCIIPushTab(viewer));
    541:     PetscCall(SNESLineSearchView(linesearch, viewer));
    542:     PetscCall(PetscViewerASCIIPopTab(viewer));
    543:   }
    544:   if (snes->npc && snes->usesnpc) {
    545:     PetscCall(PetscViewerASCIIPushTab(viewer));
    546:     PetscCall(SNESView(snes->npc, viewer));
    547:     PetscCall(PetscViewerASCIIPopTab(viewer));
    548:   }
    549:   PetscCall(PetscViewerASCIIPushTab(viewer));
    550:   PetscCall(DMGetDMSNES(snes->dm, &dmsnes));
    551:   PetscCall(DMSNESView(dmsnes, viewer));
    552:   PetscCall(PetscViewerASCIIPopTab(viewer));
    553:   if (snes->usesksp) {
    554:     PetscCall(SNESGetKSP(snes, &ksp));
    555:     PetscCall(PetscViewerASCIIPushTab(viewer));
    556:     PetscCall(KSPView(ksp, viewer));
    557:     PetscCall(PetscViewerASCIIPopTab(viewer));
    558:   }
    559:   if (isdraw) {
    560:     PetscDraw draw;
    561:     PetscCall(PetscViewerDrawGetDraw(viewer, 0, &draw));
    562:     PetscCall(PetscDrawPopCurrentPoint(draw));
    563:   }
    564:   PetscFunctionReturn(PETSC_SUCCESS);
    565: }

    567: /*
    568:   We retain a list of functions that also take SNES command
    569:   line options. These are called at the end SNESSetFromOptions()
    570: */
    571: #define MAXSETFROMOPTIONS 5
    572: static PetscInt numberofsetfromoptions;
    573: static PetscErrorCode (*othersetfromoptions[MAXSETFROMOPTIONS])(SNES);

    575: /*@C
    576:   SNESAddOptionsChecker - Adds an additional function to check for `SNES` options.

    578:   Not Collective

    580:   Input Parameter:
    581: . snescheck - function that checks for options

    583:   Calling sequence of `snescheck`:
    584: . snes - the `SNES` object for which it is checking options

    586:   Level: developer

    588: .seealso: [](ch_snes), `SNES`, `SNESSetFromOptions()`
    589: @*/
    590: PetscErrorCode SNESAddOptionsChecker(PetscErrorCode (*snescheck)(SNES snes))
    591: {
    592:   PetscFunctionBegin;
    593:   PetscCheck(numberofsetfromoptions < MAXSETFROMOPTIONS, PETSC_COMM_SELF, PETSC_ERR_ARG_OUTOFRANGE, "Too many options checkers, only %d allowed", MAXSETFROMOPTIONS);
    594:   othersetfromoptions[numberofsetfromoptions++] = snescheck;
    595:   PetscFunctionReturn(PETSC_SUCCESS);
    596: }

    598: static PetscErrorCode SNESSetUpMatrixFree_Private(SNES snes, PetscBool hasOperator, PetscInt version)
    599: {
    600:   Mat          J;
    601:   MatNullSpace nullsp;

    603:   PetscFunctionBegin;

    606:   if (!snes->vec_func && (snes->jacobian || snes->jacobian_pre)) {
    607:     Mat A = snes->jacobian, B = snes->jacobian_pre;
    608:     PetscCall(MatCreateVecs(A ? A : B, NULL, &snes->vec_func));
    609:   }

    611:   PetscCheck(version == 1 || version == 2, PETSC_COMM_SELF, PETSC_ERR_ARG_OUTOFRANGE, "matrix-free operator routines, only version 1 and 2");
    612:   if (version == 1) {
    613:     PetscCall(MatCreateSNESMF(snes, &J));
    614:     PetscCall(MatMFFDSetOptionsPrefix(J, ((PetscObject)snes)->prefix));
    615:     PetscCall(MatSetFromOptions(J));
    616:     /* TODO: the version 2 code should be merged into the MatCreateSNESMF() and MatCreateMFFD() infrastructure and then removed */
    617:   } else /* if (version == 2) */ {
    618:     PetscCheck(snes->vec_func, PETSC_COMM_SELF, PETSC_ERR_ARG_WRONGSTATE, "SNESSetFunction() must be called first");
    619: #if !defined(PETSC_USE_COMPLEX) && !defined(PETSC_USE_REAL_SINGLE) && !defined(PETSC_USE_REAL___FLOAT128) && !defined(PETSC_USE_REAL___FP16)
    620:     PetscCall(MatCreateSNESMFMore(snes, snes->vec_func, &J));
    621: #else
    622:     SETERRQ(PETSC_COMM_SELF, PETSC_ERR_SUP, "matrix-free operator routines (version 2)");
    623: #endif
    624:   }

    626:   /* attach any user provided null space that was on Amat to the newly created matrix-free matrix */
    627:   if (snes->jacobian) {
    628:     PetscCall(MatGetNullSpace(snes->jacobian, &nullsp));
    629:     if (nullsp) PetscCall(MatSetNullSpace(J, nullsp));
    630:   }

    632:   PetscCall(PetscInfo(snes, "Setting default matrix-free operator routines (version %" PetscInt_FMT ")\n", version));
    633:   if (hasOperator) {
    634:     /* This version replaces the user provided Jacobian matrix with a
    635:        matrix-free version but still employs the user-provided matrix used for computing the preconditioner. */
    636:     PetscCall(SNESSetJacobian(snes, J, NULL, NULL, NULL));
    637:   } else {
    638:     /* This version replaces both the user-provided Jacobian and the user-
    639:      provided preconditioner Jacobian with the default matrix-free version. */
    640:     if (snes->npcside == PC_LEFT && snes->npc) {
    641:       if (!snes->jacobian) PetscCall(SNESSetJacobian(snes, J, NULL, NULL, NULL));
    642:     } else {
    643:       KSP       ksp;
    644:       PC        pc;
    645:       PetscBool match;

    647:       PetscCall(SNESSetJacobian(snes, J, J, MatMFFDComputeJacobian, NULL));
    648:       /* Force no preconditioner */
    649:       PetscCall(SNESGetKSP(snes, &ksp));
    650:       PetscCall(KSPGetPC(ksp, &pc));
    651:       PetscCall(PetscObjectTypeCompareAny((PetscObject)pc, &match, PCSHELL, PCH2OPUS, ""));
    652:       if (!match) {
    653:         PetscCall(PetscInfo(snes, "Setting default matrix-free preconditioner routines\nThat is no preconditioner is being used\n"));
    654:         PetscCall(PCSetType(pc, PCNONE));
    655:       }
    656:     }
    657:   }
    658:   PetscCall(MatDestroy(&J));
    659:   PetscFunctionReturn(PETSC_SUCCESS);
    660: }

    662: static PetscErrorCode DMRestrictHook_SNESVecSol(DM dmfine, Mat Restrict, Vec Rscale, Mat Inject, DM dmcoarse, void *ctx)
    663: {
    664:   SNES snes = (SNES)ctx;
    665:   Vec  Xfine, Xfine_named = NULL, Xcoarse;

    667:   PetscFunctionBegin;
    668:   if (PetscLogPrintInfo) {
    669:     PetscInt finelevel, coarselevel, fineclevel, coarseclevel;
    670:     PetscCall(DMGetRefineLevel(dmfine, &finelevel));
    671:     PetscCall(DMGetCoarsenLevel(dmfine, &fineclevel));
    672:     PetscCall(DMGetRefineLevel(dmcoarse, &coarselevel));
    673:     PetscCall(DMGetCoarsenLevel(dmcoarse, &coarseclevel));
    674:     PetscCall(PetscInfo(dmfine, "Restricting SNES solution vector from level %" PetscInt_FMT "-%" PetscInt_FMT " to level %" PetscInt_FMT "-%" PetscInt_FMT "\n", finelevel, fineclevel, coarselevel, coarseclevel));
    675:   }
    676:   if (dmfine == snes->dm) Xfine = snes->vec_sol;
    677:   else {
    678:     PetscCall(DMGetNamedGlobalVector(dmfine, "SNESVecSol", &Xfine_named));
    679:     Xfine = Xfine_named;
    680:   }
    681:   PetscCall(DMGetNamedGlobalVector(dmcoarse, "SNESVecSol", &Xcoarse));
    682:   if (Inject) {
    683:     PetscCall(MatRestrict(Inject, Xfine, Xcoarse));
    684:   } else {
    685:     PetscCall(MatRestrict(Restrict, Xfine, Xcoarse));
    686:     PetscCall(VecPointwiseMult(Xcoarse, Xcoarse, Rscale));
    687:   }
    688:   PetscCall(DMRestoreNamedGlobalVector(dmcoarse, "SNESVecSol", &Xcoarse));
    689:   if (Xfine_named) PetscCall(DMRestoreNamedGlobalVector(dmfine, "SNESVecSol", &Xfine_named));
    690:   PetscFunctionReturn(PETSC_SUCCESS);
    691: }

    693: static PetscErrorCode DMCoarsenHook_SNESVecSol(DM dm, DM dmc, void *ctx)
    694: {
    695:   PetscFunctionBegin;
    696:   PetscCall(DMCoarsenHookAdd(dmc, DMCoarsenHook_SNESVecSol, DMRestrictHook_SNESVecSol, ctx));
    697:   PetscFunctionReturn(PETSC_SUCCESS);
    698: }

    700: /* This may be called to rediscretize the operator on levels of linear multigrid. The DM shuffle is so the user can
    701:  * safely call SNESGetDM() in their residual evaluation routine. */
    702: static PetscErrorCode KSPComputeOperators_SNES(KSP ksp, Mat A, Mat B, void *ctx)
    703: {
    704:   SNES            snes = (SNES)ctx;
    705:   DMSNES          sdm;
    706:   Vec             X, Xnamed = NULL;
    707:   DM              dmsave;
    708:   void           *ctxsave;
    709:   SNESJacobianFn *jac = NULL;

    711:   PetscFunctionBegin;
    712:   dmsave = snes->dm;
    713:   PetscCall(KSPGetDM(ksp, &snes->dm));
    714:   if (dmsave == snes->dm) X = snes->vec_sol; /* We are on the finest level */
    715:   else {
    716:     PetscBool has;

    718:     /* We are on a coarser level, this vec was initialized using a DM restrict hook */
    719:     PetscCall(DMHasNamedGlobalVector(snes->dm, "SNESVecSol", &has));
    720:     PetscCheck(has, PetscObjectComm((PetscObject)snes->dm), PETSC_ERR_PLIB, "Missing SNESVecSol");
    721:     PetscCall(DMGetNamedGlobalVector(snes->dm, "SNESVecSol", &Xnamed));
    722:     X = Xnamed;
    723:     PetscCall(SNESGetJacobian(snes, NULL, NULL, &jac, &ctxsave));
    724:     /* If the DM's don't match up, the MatFDColoring context needed for the jacobian won't match up either -- fixit. */
    725:     if (jac == SNESComputeJacobianDefaultColor) PetscCall(SNESSetJacobian(snes, NULL, NULL, SNESComputeJacobianDefaultColor, NULL));
    726:   }

    728:   /* Compute the operators */
    729:   PetscCall(DMGetDMSNES(snes->dm, &sdm));
    730:   if (Xnamed && sdm->ops->computefunction) {
    731:     /* The SNES contract with the user is that ComputeFunction is always called before ComputeJacobian.
    732:        We make sure of this here. Disable affine shift since it is for the finest level */
    733:     Vec F, saverhs = snes->vec_rhs;

    735:     snes->vec_rhs = NULL;
    736:     PetscCall(DMGetGlobalVector(snes->dm, &F));
    737:     PetscCall(SNESComputeFunction(snes, X, F));
    738:     PetscCall(DMRestoreGlobalVector(snes->dm, &F));
    739:     snes->vec_rhs = saverhs;
    740:     snes->nfuncs--; /* Do not log coarser level evaluations */
    741:   }
    742:   /* Make sure KSP DM has the Jacobian computation routine */
    743:   if (!sdm->ops->computejacobian) PetscCall(DMCopyDMSNES(dmsave, snes->dm));
    744:   PetscCall(SNESComputeJacobian(snes, X, A, B));

    746:   /* Put the previous context back */
    747:   if (snes->dm != dmsave && jac == SNESComputeJacobianDefaultColor) PetscCall(SNESSetJacobian(snes, NULL, NULL, jac, ctxsave));

    749:   if (Xnamed) PetscCall(DMRestoreNamedGlobalVector(snes->dm, "SNESVecSol", &Xnamed));
    750:   snes->dm = dmsave;
    751:   PetscFunctionReturn(PETSC_SUCCESS);
    752: }

    754: /*@
    755:   SNESSetUpMatrices - ensures that matrices are available for `SNES` Newton-like methods, this is called by `SNESSetUp_XXX()`

    757:   Collective

    759:   Input Parameter:
    760: . snes - `SNES` object to configure

    762:   Level: developer

    764:   Note:
    765:   If the matrices do not yet exist it attempts to create them based on options previously set for the `SNES` such as `-snes_mf`

    767:   Developer Note:
    768:   The functionality of this routine overlaps in a confusing way with the functionality of `SNESSetUpMatrixFree_Private()` which is called by
    769:   `SNESSetUp()` but sometimes `SNESSetUpMatrices()` is called without `SNESSetUp()` being called. A refactorization to simplify the
    770:   logic that handles the matrix-free case is desirable.

    772: .seealso: [](ch_snes), `SNES`, `SNESSetUp()`
    773: @*/
    774: PetscErrorCode SNESSetUpMatrices(SNES snes)
    775: {
    776:   DM     dm;
    777:   DMSNES sdm;

    779:   PetscFunctionBegin;
    780:   PetscCall(SNESGetDM(snes, &dm));
    781:   PetscCall(DMGetDMSNES(dm, &sdm));
    782:   if (!snes->jacobian && snes->mf && !snes->mf_operator && !snes->jacobian_pre) {
    783:     Mat   J;
    784:     void *functx;
    785:     PetscCall(MatCreateSNESMF(snes, &J));
    786:     PetscCall(MatMFFDSetOptionsPrefix(J, ((PetscObject)snes)->prefix));
    787:     PetscCall(MatSetFromOptions(J));
    788:     PetscCall(SNESGetFunction(snes, NULL, NULL, &functx));
    789:     PetscCall(SNESSetJacobian(snes, J, J, NULL, NULL));
    790:     PetscCall(MatDestroy(&J));
    791:   } else if (snes->mf_operator && !snes->jacobian_pre && !snes->jacobian) {
    792:     Mat J, B;
    793:     PetscCall(MatCreateSNESMF(snes, &J));
    794:     PetscCall(MatMFFDSetOptionsPrefix(J, ((PetscObject)snes)->prefix));
    795:     PetscCall(MatSetFromOptions(J));
    796:     PetscCall(DMCreateMatrix(snes->dm, &B));
    797:     /* sdm->computejacobian was already set to reach here */
    798:     PetscCall(SNESSetJacobian(snes, J, B, NULL, NULL));
    799:     PetscCall(MatDestroy(&J));
    800:     PetscCall(MatDestroy(&B));
    801:   } else if (!snes->jacobian_pre) {
    802:     PetscDS   prob;
    803:     Mat       J, B;
    804:     PetscBool hasPrec = PETSC_FALSE;

    806:     J = snes->jacobian;
    807:     PetscCall(DMGetDS(dm, &prob));
    808:     if (prob) PetscCall(PetscDSHasJacobianPreconditioner(prob, &hasPrec));
    809:     if (J) PetscCall(PetscObjectReference((PetscObject)J));
    810:     else if (hasPrec) PetscCall(DMCreateMatrix(snes->dm, &J));
    811:     PetscCall(DMCreateMatrix(snes->dm, &B));
    812:     PetscCall(SNESSetJacobian(snes, J ? J : B, B, NULL, NULL));
    813:     PetscCall(MatDestroy(&J));
    814:     PetscCall(MatDestroy(&B));
    815:   }
    816:   {
    817:     KSP ksp;
    818:     PetscCall(SNESGetKSP(snes, &ksp));
    819:     PetscCall(KSPSetComputeOperators(ksp, KSPComputeOperators_SNES, snes));
    820:     PetscCall(DMCoarsenHookAdd(snes->dm, DMCoarsenHook_SNESVecSol, DMRestrictHook_SNESVecSol, snes));
    821:   }
    822:   PetscFunctionReturn(PETSC_SUCCESS);
    823: }

    825: PETSC_SINGLE_LIBRARY_INTERN PetscErrorCode PetscMonitorPauseFinal_Internal(PetscInt, void *);

    827: static PetscErrorCode SNESMonitorPauseFinal_Internal(SNES snes)
    828: {
    829:   PetscFunctionBegin;
    830:   if (!snes->pauseFinal) PetscFunctionReturn(PETSC_SUCCESS);
    831:   PetscCall(PetscMonitorPauseFinal_Internal(snes->numbermonitors, snes->monitorcontext));
    832:   PetscFunctionReturn(PETSC_SUCCESS);
    833: }

    835: /*@C
    836:   SNESMonitorSetFromOptions - Sets a monitor function and viewer appropriate for the type indicated by the user

    838:   Collective

    840:   Input Parameters:
    841: + snes         - `SNES` object you wish to monitor
    842: . name         - the monitor type one is seeking
    843: . help         - message indicating what monitoring is done
    844: . manual       - manual page for the monitor
    845: . monitor      - the monitor function, this must use a `PetscViewerFormat` as its context
    846: - monitorsetup - a function that is called once ONLY if the user selected this monitor that may set additional features of the `SNES` or `PetscViewer` objects

    848:   Calling sequence of `monitor`:
    849: + snes - the nonlinear solver context
    850: . it   - the current iteration
    851: . r    - the current function norm
    852: - vf   - a `PetscViewerAndFormat` struct that contains the `PetscViewer` and `PetscViewerFormat` to use

    854:   Calling sequence of `monitorsetup`:
    855: + snes - the nonlinear solver context
    856: - vf   - a `PetscViewerAndFormat` struct that contains the `PetscViewer` and `PetscViewerFormat` to use

    858:   Options Database Key:
    859: . -name - trigger the use of this monitor in `SNESSetFromOptions()`

    861:   Level: advanced

    863: .seealso: [](ch_snes), `PetscOptionsCreateViewer()`, `PetscOptionsGetReal()`, `PetscOptionsHasName()`, `PetscOptionsGetString()`,
    864:           `PetscOptionsGetIntArray()`, `PetscOptionsGetRealArray()`, `PetscOptionsBool()`
    865:           `PetscOptionsInt()`, `PetscOptionsString()`, `PetscOptionsReal()`,
    866:           `PetscOptionsName()`, `PetscOptionsBegin()`, `PetscOptionsEnd()`, `PetscOptionsHeadBegin()`,
    867:           `PetscOptionsStringArray()`, `PetscOptionsRealArray()`, `PetscOptionsScalar()`,
    868:           `PetscOptionsBoolGroupBegin()`, `PetscOptionsBoolGroup()`, `PetscOptionsBoolGroupEnd()`,
    869:           `PetscOptionsFList()`, `PetscOptionsEList()`
    870: @*/
    871: PetscErrorCode SNESMonitorSetFromOptions(SNES snes, const char name[], const char help[], const char manual[], PetscErrorCode (*monitor)(SNES snes, PetscInt it, PetscReal r, PetscViewerAndFormat *vf), PetscErrorCode (*monitorsetup)(SNES snes, PetscViewerAndFormat *vf))
    872: {
    873:   PetscViewer       viewer;
    874:   PetscViewerFormat format;
    875:   PetscBool         flg;

    877:   PetscFunctionBegin;
    878:   PetscCall(PetscOptionsCreateViewer(PetscObjectComm((PetscObject)snes), ((PetscObject)snes)->options, ((PetscObject)snes)->prefix, name, &viewer, &format, &flg));
    879:   if (flg) {
    880:     PetscViewerAndFormat *vf;
    881:     PetscCall(PetscViewerAndFormatCreate(viewer, format, &vf));
    882:     PetscCall(PetscViewerDestroy(&viewer));
    883:     if (monitorsetup) PetscCall((*monitorsetup)(snes, vf));
    884:     PetscCall(SNESMonitorSet(snes, (PetscErrorCode (*)(SNES, PetscInt, PetscReal, void *))monitor, vf, (PetscCtxDestroyFn *)PetscViewerAndFormatDestroy));
    885:   }
    886:   PetscFunctionReturn(PETSC_SUCCESS);
    887: }

    889: PetscErrorCode SNESEWSetFromOptions_Private(SNESKSPEW *kctx, PetscBool print_api, MPI_Comm comm, const char *prefix)
    890: {
    891:   const char *api = print_api ? "SNESKSPSetParametersEW" : NULL;

    893:   PetscFunctionBegin;
    894:   PetscOptionsBegin(comm, prefix, "Eisenstat and Walker type forcing options", "KSP");
    895:   PetscCall(PetscOptionsInt("-ksp_ew_version", "Version 1, 2 or 3", api, kctx->version, &kctx->version, NULL));
    896:   PetscCall(PetscOptionsReal("-ksp_ew_rtol0", "0 <= rtol0 < 1", api, kctx->rtol_0, &kctx->rtol_0, NULL));
    897:   kctx->rtol_max = PetscMax(kctx->rtol_0, kctx->rtol_max);
    898:   PetscCall(PetscOptionsReal("-ksp_ew_rtolmax", "0 <= rtolmax < 1", api, kctx->rtol_max, &kctx->rtol_max, NULL));
    899:   PetscCall(PetscOptionsReal("-ksp_ew_gamma", "0 <= gamma <= 1", api, kctx->gamma, &kctx->gamma, NULL));
    900:   PetscCall(PetscOptionsReal("-ksp_ew_alpha", "1 < alpha <= 2", api, kctx->alpha, &kctx->alpha, NULL));
    901:   PetscCall(PetscOptionsReal("-ksp_ew_alpha2", "alpha2", NULL, kctx->alpha2, &kctx->alpha2, NULL));
    902:   PetscCall(PetscOptionsReal("-ksp_ew_threshold", "0 < threshold < 1", api, kctx->threshold, &kctx->threshold, NULL));
    903:   PetscCall(PetscOptionsReal("-ksp_ew_v4_p1", "p1", NULL, kctx->v4_p1, &kctx->v4_p1, NULL));
    904:   PetscCall(PetscOptionsReal("-ksp_ew_v4_p2", "p2", NULL, kctx->v4_p2, &kctx->v4_p2, NULL));
    905:   PetscCall(PetscOptionsReal("-ksp_ew_v4_p3", "p3", NULL, kctx->v4_p3, &kctx->v4_p3, NULL));
    906:   PetscCall(PetscOptionsReal("-ksp_ew_v4_m1", "Scaling when rk-1 in [p2,p3)", NULL, kctx->v4_m1, &kctx->v4_m1, NULL));
    907:   PetscCall(PetscOptionsReal("-ksp_ew_v4_m2", "Scaling when rk-1 in [p3,+infty)", NULL, kctx->v4_m2, &kctx->v4_m2, NULL));
    908:   PetscCall(PetscOptionsReal("-ksp_ew_v4_m3", "Threshold for successive rtol (0.1 in Eq.7)", NULL, kctx->v4_m3, &kctx->v4_m3, NULL));
    909:   PetscCall(PetscOptionsReal("-ksp_ew_v4_m4", "Adaptation scaling (0.5 in Eq.7)", NULL, kctx->v4_m4, &kctx->v4_m4, NULL));
    910:   PetscOptionsEnd();
    911:   PetscFunctionReturn(PETSC_SUCCESS);
    912: }

    914: /*@
    915:   SNESSetFromOptions - Sets various `SNES` and `KSP` parameters from user options.

    917:   Collective

    919:   Input Parameter:
    920: . snes - the `SNES` context

    922:   Options Database Keys:
    923: + -snes_type <type>                                                            - newtonls, newtontr, ngmres, ncg, nrichardson, qn, vi, fas, `SNESType` for complete list
    924: . -snes_rtol <rtol>                                                            - relative decrease in tolerance norm from initial
    925: . -snes_atol <abstol>                                                          - absolute tolerance of residual norm
    926: . -snes_stol <stol>                                                            - convergence tolerance in terms of the norm of the change in the solution between steps
    927: . -snes_divergence_tolerance <divtol>                                          - if the residual goes above divtol*rnorm0, exit with divergence
    928: . -snes_max_it <max_it>                                                        - maximum number of iterations
    929: . -snes_max_funcs <max_funcs>                                                  - maximum number of function evaluations
    930: . -snes_force_iteration <force>                                                - force `SNESSolve()` to take at least one iteration
    931: . -snes_max_fail <max_fail>                                                    - maximum number of line search failures allowed before stopping, default is none
    932: . -snes_max_linear_solve_fail                                                  - number of linear solver failures before SNESSolve() stops
    933: . -snes_lag_preconditioner <lag>                                               - how often preconditioner is rebuilt (use -1 to never rebuild)
    934: . -snes_lag_preconditioner_persists <true,false>                               - retains the -snes_lag_preconditioner information across multiple SNESSolve()
    935: . -snes_lag_jacobian <lag>                                                     - how often Jacobian is rebuilt (use -1 to never rebuild)
    936: . -snes_lag_jacobian_persists <true,false>                                     - retains the -snes_lag_jacobian information across multiple SNESSolve()
    937: . -snes_convergence_test <default,skip,correct_pressure>                       - convergence test in nonlinear solver. default `SNESConvergedDefault()`. skip `SNESConvergedSkip()` means continue iterating until max_it or some other criterion is reached, saving expense of convergence test. correct_pressure `SNESConvergedCorrectPressure()` has special handling of a pressure null space.
    938: . -snes_monitor [ascii][:filename][:viewer format]                             - prints residual norm at each iteration. if no filename given prints to stdout
    939: . -snes_monitor_solution [ascii binary draw][:filename][:viewer format]        - plots solution at each iteration
    940: . -snes_monitor_residual [ascii binary draw][:filename][:viewer format]        - plots residual (not its norm) at each iteration
    941: . -snes_monitor_solution_update [ascii binary draw][:filename][:viewer format] - plots update to solution at each iteration
    942: . -snes_monitor_lg_residualnorm                                                - plots residual norm at each iteration
    943: . -snes_monitor_lg_range                                                       - plots residual norm at each iteration
    944: . -snes_monitor_pause_final                                                    - Pauses all monitor drawing after the solver ends
    945: . -snes_fd                                                                     - use finite differences to compute Jacobian; very slow, only for testing
    946: . -snes_fd_color                                                               - use finite differences with coloring to compute Jacobian
    947: . -snes_mf_ksp_monitor                                                         - if using matrix-free multiply then print h at each `KSP` iteration
    948: . -snes_converged_reason                                                       - print the reason for convergence/divergence after each solve
    949: . -npc_snes_type <type>                                                        - the `SNES` type to use as a nonlinear preconditioner
    950: . -snes_test_jacobian <optional threshold>                                     - compare the user provided Jacobian with one computed via finite differences to check for errors.  If a threshold is given, display only those entries whose difference is greater than the threshold.
    951: - -snes_test_jacobian_view                                                     - display the user provided Jacobian, the finite difference Jacobian and the difference between them to help users detect the location of errors in the user provided Jacobian.

    953:   Options Database Keys for Eisenstat-Walker method:
    954: + -snes_ksp_ew                       - use Eisenstat-Walker method for determining linear system convergence
    955: . -snes_ksp_ew_version ver           - version of  Eisenstat-Walker method
    956: . -snes_ksp_ew_rtol0 <rtol0>         - Sets rtol0
    957: . -snes_ksp_ew_rtolmax <rtolmax>     - Sets rtolmax
    958: . -snes_ksp_ew_gamma <gamma>         - Sets gamma
    959: . -snes_ksp_ew_alpha <alpha>         - Sets alpha
    960: . -snes_ksp_ew_alpha2 <alpha2>       - Sets alpha2
    961: - -snes_ksp_ew_threshold <threshold> - Sets threshold

    963:   Level: beginner

    965:   Notes:
    966:   To see all options, run your program with the -help option or consult the users manual

    968:   `SNES` supports three approaches for computing (approximate) Jacobians: user provided via `SNESSetJacobian()`, matrix-free using `MatCreateSNESMF()`,
    969:   and computing explicitly with
    970:   finite differences and coloring using `MatFDColoring`. It is also possible to use automatic differentiation and the `MatFDColoring` object.

    972: .seealso: [](ch_snes), `SNESType`, `SNESSetOptionsPrefix()`, `SNESResetFromOptions()`, `SNES`, `SNESCreate()`, `MatCreateSNESMF()`, `MatFDColoring`
    973: @*/
    974: PetscErrorCode SNESSetFromOptions(SNES snes)
    975: {
    976:   PetscBool   flg, pcset, persist, set;
    977:   PetscInt    i, indx, lag, grids, max_its, max_funcs;
    978:   const char *deft        = SNESNEWTONLS;
    979:   const char *convtests[] = {"default", "skip", "correct_pressure"};
    980:   SNESKSPEW  *kctx        = NULL;
    981:   char        type[256], monfilename[PETSC_MAX_PATH_LEN], ewprefix[256];
    982:   PCSide      pcside;
    983:   const char *optionsprefix;
    984:   PetscReal   rtol, abstol, stol;

    986:   PetscFunctionBegin;
    988:   PetscCall(SNESRegisterAll());
    989:   PetscObjectOptionsBegin((PetscObject)snes);
    990:   if (((PetscObject)snes)->type_name) deft = ((PetscObject)snes)->type_name;
    991:   PetscCall(PetscOptionsFList("-snes_type", "Nonlinear solver method", "SNESSetType", SNESList, deft, type, 256, &flg));
    992:   if (flg) {
    993:     PetscCall(SNESSetType(snes, type));
    994:   } else if (!((PetscObject)snes)->type_name) {
    995:     PetscCall(SNESSetType(snes, deft));
    996:   }

    998:   abstol    = snes->abstol;
    999:   rtol      = snes->rtol;
    1000:   stol      = snes->stol;
    1001:   max_its   = snes->max_its;
    1002:   max_funcs = snes->max_funcs;
    1003:   PetscCall(PetscOptionsReal("-snes_rtol", "Stop if decrease in function norm less than", "SNESSetTolerances", snes->rtol, &rtol, NULL));
    1004:   PetscCall(PetscOptionsReal("-snes_atol", "Stop if function norm less than", "SNESSetTolerances", snes->abstol, &abstol, NULL));
    1005:   PetscCall(PetscOptionsReal("-snes_stol", "Stop if step length less than", "SNESSetTolerances", snes->stol, &stol, NULL));
    1006:   PetscCall(PetscOptionsInt("-snes_max_it", "Maximum iterations", "SNESSetTolerances", snes->max_its, &max_its, NULL));
    1007:   PetscCall(PetscOptionsInt("-snes_max_funcs", "Maximum function evaluations", "SNESSetTolerances", snes->max_funcs, &max_funcs, NULL));
    1008:   PetscCall(SNESSetTolerances(snes, abstol, rtol, stol, max_its, max_funcs));

    1010:   PetscCall(PetscOptionsReal("-snes_divergence_tolerance", "Stop if residual norm increases by this factor", "SNESSetDivergenceTolerance", snes->divtol, &snes->divtol, &flg));
    1011:   if (flg) PetscCall(SNESSetDivergenceTolerance(snes, snes->divtol));

    1013:   PetscCall(PetscOptionsInt("-snes_max_fail", "Maximum nonlinear step failures", "SNESSetMaxNonlinearStepFailures", snes->maxFailures, &snes->maxFailures, &flg));
    1014:   if (flg) PetscCall(SNESSetMaxNonlinearStepFailures(snes, snes->maxFailures));

    1016:   PetscCall(PetscOptionsInt("-snes_max_linear_solve_fail", "Maximum failures in linear solves allowed", "SNESSetMaxLinearSolveFailures", snes->maxLinearSolveFailures, &snes->maxLinearSolveFailures, &flg));
    1017:   if (flg) PetscCall(SNESSetMaxLinearSolveFailures(snes, snes->maxLinearSolveFailures));

    1019:   PetscCall(PetscOptionsBool("-snes_error_if_not_converged", "Generate error if solver does not converge", "SNESSetErrorIfNotConverged", snes->errorifnotconverged, &snes->errorifnotconverged, NULL));
    1020:   PetscCall(PetscOptionsBool("-snes_force_iteration", "Force SNESSolve() to take at least one iteration", "SNESSetForceIteration", snes->forceiteration, &snes->forceiteration, NULL));
    1021:   PetscCall(PetscOptionsBool("-snes_check_jacobian_domain_error", "Check Jacobian domain error after Jacobian evaluation", "SNESCheckJacobianDomainError", snes->checkjacdomainerror, &snes->checkjacdomainerror, NULL));

    1023:   PetscCall(PetscOptionsInt("-snes_lag_preconditioner", "How often to rebuild preconditioner", "SNESSetLagPreconditioner", snes->lagpreconditioner, &lag, &flg));
    1024:   if (flg) {
    1025:     PetscCheck(lag != -1, PetscObjectComm((PetscObject)snes), PETSC_ERR_USER, "Cannot set the lag to -1 from the command line since the preconditioner must be built as least once, perhaps you mean -2");
    1026:     PetscCall(SNESSetLagPreconditioner(snes, lag));
    1027:   }
    1028:   PetscCall(PetscOptionsBool("-snes_lag_preconditioner_persists", "Preconditioner lagging through multiple SNES solves", "SNESSetLagPreconditionerPersists", snes->lagjac_persist, &persist, &flg));
    1029:   if (flg) PetscCall(SNESSetLagPreconditionerPersists(snes, persist));
    1030:   PetscCall(PetscOptionsInt("-snes_lag_jacobian", "How often to rebuild Jacobian", "SNESSetLagJacobian", snes->lagjacobian, &lag, &flg));
    1031:   if (flg) {
    1032:     PetscCheck(lag != -1, PetscObjectComm((PetscObject)snes), PETSC_ERR_USER, "Cannot set the lag to -1 from the command line since the Jacobian must be built as least once, perhaps you mean -2");
    1033:     PetscCall(SNESSetLagJacobian(snes, lag));
    1034:   }
    1035:   PetscCall(PetscOptionsBool("-snes_lag_jacobian_persists", "Jacobian lagging through multiple SNES solves", "SNESSetLagJacobianPersists", snes->lagjac_persist, &persist, &flg));
    1036:   if (flg) PetscCall(SNESSetLagJacobianPersists(snes, persist));

    1038:   PetscCall(PetscOptionsInt("-snes_grid_sequence", "Use grid sequencing to generate initial guess", "SNESSetGridSequence", snes->gridsequence, &grids, &flg));
    1039:   if (flg) PetscCall(SNESSetGridSequence(snes, grids));

    1041:   PetscCall(PetscOptionsEList("-snes_convergence_test", "Convergence test", "SNESSetConvergenceTest", convtests, PETSC_STATIC_ARRAY_LENGTH(convtests), "default", &indx, &flg));
    1042:   if (flg) {
    1043:     switch (indx) {
    1044:     case 0:
    1045:       PetscCall(SNESSetConvergenceTest(snes, SNESConvergedDefault, NULL, NULL));
    1046:       break;
    1047:     case 1:
    1048:       PetscCall(SNESSetConvergenceTest(snes, SNESConvergedSkip, NULL, NULL));
    1049:       break;
    1050:     case 2:
    1051:       PetscCall(SNESSetConvergenceTest(snes, SNESConvergedCorrectPressure, NULL, NULL));
    1052:       break;
    1053:     }
    1054:   }

    1056:   PetscCall(PetscOptionsEList("-snes_norm_schedule", "SNES Norm schedule", "SNESSetNormSchedule", SNESNormSchedules, 5, "function", &indx, &flg));
    1057:   if (flg) PetscCall(SNESSetNormSchedule(snes, (SNESNormSchedule)indx));

    1059:   PetscCall(PetscOptionsEList("-snes_function_type", "SNES Norm schedule", "SNESSetFunctionType", SNESFunctionTypes, 2, "unpreconditioned", &indx, &flg));
    1060:   if (flg) PetscCall(SNESSetFunctionType(snes, (SNESFunctionType)indx));

    1062:   kctx = (SNESKSPEW *)snes->kspconvctx;

    1064:   PetscCall(PetscOptionsBool("-snes_ksp_ew", "Use Eisentat-Walker linear system convergence test", "SNESKSPSetUseEW", snes->ksp_ewconv, &snes->ksp_ewconv, NULL));

    1066:   PetscCall(SNESGetOptionsPrefix(snes, &optionsprefix));
    1067:   PetscCall(PetscSNPrintf(ewprefix, sizeof(ewprefix), "%s%s", optionsprefix ? optionsprefix : "", "snes_"));
    1068:   PetscCall(SNESEWSetFromOptions_Private(kctx, PETSC_TRUE, PetscObjectComm((PetscObject)snes), ewprefix));

    1070:   flg = PETSC_FALSE;
    1071:   PetscCall(PetscOptionsBool("-snes_monitor_cancel", "Remove all monitors", "SNESMonitorCancel", flg, &flg, &set));
    1072:   if (set && flg) PetscCall(SNESMonitorCancel(snes));

    1074:   PetscCall(SNESMonitorSetFromOptions(snes, "-snes_monitor", "Monitor norm of function", "SNESMonitorDefault", SNESMonitorDefault, SNESMonitorDefaultSetUp));
    1075:   PetscCall(SNESMonitorSetFromOptions(snes, "-snes_monitor_short", "Monitor norm of function with fewer digits", "SNESMonitorDefaultShort", SNESMonitorDefaultShort, NULL));
    1076:   PetscCall(SNESMonitorSetFromOptions(snes, "-snes_monitor_range", "Monitor range of elements of function", "SNESMonitorRange", SNESMonitorRange, NULL));

    1078:   PetscCall(SNESMonitorSetFromOptions(snes, "-snes_monitor_ratio", "Monitor ratios of the norm of function for consecutive steps", "SNESMonitorRatio", SNESMonitorRatio, SNESMonitorRatioSetUp));
    1079:   PetscCall(SNESMonitorSetFromOptions(snes, "-snes_monitor_field", "Monitor norm of function (split into fields)", "SNESMonitorDefaultField", SNESMonitorDefaultField, NULL));
    1080:   PetscCall(SNESMonitorSetFromOptions(snes, "-snes_monitor_solution", "View solution at each iteration", "SNESMonitorSolution", SNESMonitorSolution, NULL));
    1081:   PetscCall(SNESMonitorSetFromOptions(snes, "-snes_monitor_solution_update", "View correction at each iteration", "SNESMonitorSolutionUpdate", SNESMonitorSolutionUpdate, NULL));
    1082:   PetscCall(SNESMonitorSetFromOptions(snes, "-snes_monitor_residual", "View residual at each iteration", "SNESMonitorResidual", SNESMonitorResidual, NULL));
    1083:   PetscCall(SNESMonitorSetFromOptions(snes, "-snes_monitor_jacupdate_spectrum", "Print the change in the spectrum of the Jacobian", "SNESMonitorJacUpdateSpectrum", SNESMonitorJacUpdateSpectrum, NULL));
    1084:   PetscCall(SNESMonitorSetFromOptions(snes, "-snes_monitor_fields", "Monitor norm of function per field", "SNESMonitorSet", SNESMonitorFields, NULL));
    1085:   PetscCall(PetscOptionsBool("-snes_monitor_pause_final", "Pauses all draw monitors at the final iterate", "SNESMonitorPauseFinal_Internal", PETSC_FALSE, &snes->pauseFinal, NULL));

    1087:   PetscCall(PetscOptionsString("-snes_monitor_python", "Use Python function", "SNESMonitorSet", NULL, monfilename, sizeof(monfilename), &flg));
    1088:   if (flg) PetscCall(PetscPythonMonitorSet((PetscObject)snes, monfilename));

    1090:   flg = PETSC_FALSE;
    1091:   PetscCall(PetscOptionsBool("-snes_monitor_lg_range", "Plot function range at each iteration", "SNESMonitorLGRange", flg, &flg, NULL));
    1092:   if (flg) {
    1093:     PetscViewer ctx;

    1095:     PetscCall(PetscViewerDrawOpen(PetscObjectComm((PetscObject)snes), NULL, NULL, PETSC_DECIDE, PETSC_DECIDE, 400, 300, &ctx));
    1096:     PetscCall(SNESMonitorSet(snes, SNESMonitorLGRange, ctx, (PetscCtxDestroyFn *)PetscViewerDestroy));
    1097:   }

    1099:   PetscCall(PetscViewerDestroy(&snes->convergedreasonviewer));
    1100:   PetscCall(PetscOptionsCreateViewer(PetscObjectComm((PetscObject)snes), ((PetscObject)snes)->options, ((PetscObject)snes)->prefix, "-snes_converged_reason", &snes->convergedreasonviewer, &snes->convergedreasonformat, NULL));
    1101:   flg = PETSC_FALSE;
    1102:   PetscCall(PetscOptionsBool("-snes_converged_reason_view_cancel", "Remove all converged reason viewers", "SNESConvergedReasonViewCancel", flg, &flg, &set));
    1103:   if (set && flg) PetscCall(SNESConvergedReasonViewCancel(snes));

    1105:   flg = PETSC_FALSE;
    1106:   PetscCall(PetscOptionsBool("-snes_fd", "Use finite differences (slow) to compute Jacobian", "SNESComputeJacobianDefault", flg, &flg, NULL));
    1107:   if (flg) {
    1108:     void *functx;
    1109:     DM    dm;
    1110:     PetscCall(SNESGetDM(snes, &dm));
    1111:     PetscCall(DMSNESUnsetJacobianContext_Internal(dm));
    1112:     PetscCall(SNESGetFunction(snes, NULL, NULL, &functx));
    1113:     PetscCall(SNESSetJacobian(snes, snes->jacobian, snes->jacobian_pre, SNESComputeJacobianDefault, functx));
    1114:     PetscCall(PetscInfo(snes, "Setting default finite difference Jacobian matrix\n"));
    1115:   }

    1117:   flg = PETSC_FALSE;
    1118:   PetscCall(PetscOptionsBool("-snes_fd_function", "Use finite differences (slow) to compute function from user objective", "SNESObjectiveComputeFunctionDefaultFD", flg, &flg, NULL));
    1119:   if (flg) PetscCall(SNESSetFunction(snes, NULL, SNESObjectiveComputeFunctionDefaultFD, NULL));

    1121:   flg = PETSC_FALSE;
    1122:   PetscCall(PetscOptionsBool("-snes_fd_color", "Use finite differences with coloring to compute Jacobian", "SNESComputeJacobianDefaultColor", flg, &flg, NULL));
    1123:   if (flg) {
    1124:     DM dm;
    1125:     PetscCall(SNESGetDM(snes, &dm));
    1126:     PetscCall(DMSNESUnsetJacobianContext_Internal(dm));
    1127:     PetscCall(SNESSetJacobian(snes, snes->jacobian, snes->jacobian_pre, SNESComputeJacobianDefaultColor, NULL));
    1128:     PetscCall(PetscInfo(snes, "Setting default finite difference coloring Jacobian matrix\n"));
    1129:   }

    1131:   flg = PETSC_FALSE;
    1132:   PetscCall(PetscOptionsBool("-snes_mf_operator", "Use a Matrix-Free Jacobian with user-provided matrix for computing the preconditioner", "SNESSetUseMatrixFree", PETSC_FALSE, &snes->mf_operator, &flg));
    1133:   if (flg && snes->mf_operator) {
    1134:     snes->mf_operator = PETSC_TRUE;
    1135:     snes->mf          = PETSC_TRUE;
    1136:   }
    1137:   flg = PETSC_FALSE;
    1138:   PetscCall(PetscOptionsBool("-snes_mf", "Use a Matrix-Free Jacobian with no matrix for computing the preconditioner", "SNESSetUseMatrixFree", PETSC_FALSE, &snes->mf, &flg));
    1139:   if (!flg && snes->mf_operator) snes->mf = PETSC_TRUE;
    1140:   PetscCall(PetscOptionsInt("-snes_mf_version", "Matrix-Free routines version 1 or 2", "None", snes->mf_version, &snes->mf_version, NULL));

    1142:   PetscCall(PetscOptionsName("-snes_test_function", "Compare hand-coded and finite difference functions", "None", &snes->testFunc));
    1143:   PetscCall(PetscOptionsName("-snes_test_jacobian", "Compare hand-coded and finite difference Jacobians", "None", &snes->testJac));

    1145:   flg = PETSC_FALSE;
    1146:   PetscCall(SNESGetNPCSide(snes, &pcside));
    1147:   PetscCall(PetscOptionsEnum("-snes_npc_side", "SNES nonlinear preconditioner side", "SNESSetNPCSide", PCSides, (PetscEnum)pcside, (PetscEnum *)&pcside, &flg));
    1148:   if (flg) PetscCall(SNESSetNPCSide(snes, pcside));

    1150: #if defined(PETSC_HAVE_SAWS)
    1151:   /*
    1152:     Publish convergence information using SAWs
    1153:   */
    1154:   flg = PETSC_FALSE;
    1155:   PetscCall(PetscOptionsBool("-snes_monitor_saws", "Publish SNES progress using SAWs", "SNESMonitorSet", flg, &flg, NULL));
    1156:   if (flg) {
    1157:     void *ctx;
    1158:     PetscCall(SNESMonitorSAWsCreate(snes, &ctx));
    1159:     PetscCall(SNESMonitorSet(snes, SNESMonitorSAWs, ctx, SNESMonitorSAWsDestroy));
    1160:   }
    1161: #endif
    1162: #if defined(PETSC_HAVE_SAWS)
    1163:   {
    1164:     PetscBool set;
    1165:     flg = PETSC_FALSE;
    1166:     PetscCall(PetscOptionsBool("-snes_saws_block", "Block for SAWs at end of SNESSolve", "PetscObjectSAWsBlock", ((PetscObject)snes)->amspublishblock, &flg, &set));
    1167:     if (set) PetscCall(PetscObjectSAWsSetBlock((PetscObject)snes, flg));
    1168:   }
    1169: #endif

    1171:   for (i = 0; i < numberofsetfromoptions; i++) PetscCall((*othersetfromoptions[i])(snes));

    1173:   PetscTryTypeMethod(snes, setfromoptions, PetscOptionsObject);

    1175:   /* process any options handlers added with PetscObjectAddOptionsHandler() */
    1176:   PetscCall(PetscObjectProcessOptionsHandlers((PetscObject)snes, PetscOptionsObject));
    1177:   PetscOptionsEnd();

    1179:   if (snes->linesearch) {
    1180:     PetscCall(SNESGetLineSearch(snes, &snes->linesearch));
    1181:     PetscCall(SNESLineSearchSetFromOptions(snes->linesearch));
    1182:   }

    1184:   if (snes->usesksp) {
    1185:     if (!snes->ksp) PetscCall(SNESGetKSP(snes, &snes->ksp));
    1186:     PetscCall(KSPSetOperators(snes->ksp, snes->jacobian, snes->jacobian_pre));
    1187:     PetscCall(KSPSetFromOptions(snes->ksp));
    1188:   }

    1190:   /* if user has set the SNES NPC type via options database, create it. */
    1191:   PetscCall(SNESGetOptionsPrefix(snes, &optionsprefix));
    1192:   PetscCall(PetscOptionsHasName(((PetscObject)snes)->options, optionsprefix, "-npc_snes_type", &pcset));
    1193:   if (pcset && (!snes->npc)) PetscCall(SNESGetNPC(snes, &snes->npc));
    1194:   if (snes->npc) PetscCall(SNESSetFromOptions(snes->npc));
    1195:   snes->setfromoptionscalled++;
    1196:   PetscFunctionReturn(PETSC_SUCCESS);
    1197: }

    1199: /*@
    1200:   SNESResetFromOptions - Sets various `SNES` and `KSP` parameters from user options ONLY if the `SNESSetFromOptions()` was previously called

    1202:   Collective

    1204:   Input Parameter:
    1205: . snes - the `SNES` context

    1207:   Level: advanced

    1209: .seealso: [](ch_snes), `SNES`, `SNESSetFromOptions()`, `SNESSetOptionsPrefix()`
    1210: @*/
    1211: PetscErrorCode SNESResetFromOptions(SNES snes)
    1212: {
    1213:   PetscFunctionBegin;
    1214:   if (snes->setfromoptionscalled) PetscCall(SNESSetFromOptions(snes));
    1215:   PetscFunctionReturn(PETSC_SUCCESS);
    1216: }

    1218: /*@C
    1219:   SNESSetComputeApplicationContext - Sets an optional function to compute a user-defined context for
    1220:   the nonlinear solvers.

    1222:   Logically Collective; No Fortran Support

    1224:   Input Parameters:
    1225: + snes    - the `SNES` context
    1226: . compute - function to compute the context
    1227: - destroy - function to destroy the context, see `PetscCtxDestroyFn` for the calling sequence

    1229:   Calling sequence of `compute`:
    1230: + snes - the `SNES` context
    1231: - ctx  - context to be computed

    1233:   Level: intermediate

    1235:   Note:
    1236:   This routine is useful if you are performing grid sequencing or using `SNESFAS` and need the appropriate context generated for each level.

    1238:   Use `SNESSetApplicationContext()` to see the context immediately

    1240: .seealso: [](ch_snes), `SNESGetApplicationContext()`, `SNESSetApplicationContext()`, `PetscCtxDestroyFn`
    1241: @*/
    1242: PetscErrorCode SNESSetComputeApplicationContext(SNES snes, PetscErrorCode (*compute)(SNES snes, void **ctx), PetscCtxDestroyFn *destroy)
    1243: {
    1244:   PetscFunctionBegin;
    1246:   snes->ops->usercompute = compute;
    1247:   snes->ops->ctxdestroy  = destroy;
    1248:   PetscFunctionReturn(PETSC_SUCCESS);
    1249: }

    1251: /*@
    1252:   SNESSetApplicationContext - Sets the optional user-defined context for the nonlinear solvers.

    1254:   Logically Collective

    1256:   Input Parameters:
    1257: + snes - the `SNES` context
    1258: - ctx  - the user context

    1260:   Level: intermediate

    1262:   Notes:
    1263:   Users can provide a context when constructing the `SNES` options and then access it inside their function, Jacobian computation, or other evaluation function
    1264:   with `SNESGetApplicationContext()`

    1266:   To provide a function that computes the context for you use `SNESSetComputeApplicationContext()`

    1268:   Fortran Note:
    1269:   This only works when `ctx` is a Fortran derived type (it cannot be a `PetscObject`), we recommend writing a Fortran interface definition for this
    1270:   function that tells the Fortran compiler the derived data type that is passed in as the `ctx` argument. See `SNESGetApplicationContext()` for
    1271:   an example.

    1273: .seealso: [](ch_snes), `SNES`, `SNESSetComputeApplicationContext()`, `SNESGetApplicationContext()`
    1274: @*/
    1275: PetscErrorCode SNESSetApplicationContext(SNES snes, void *ctx)
    1276: {
    1277:   KSP ksp;

    1279:   PetscFunctionBegin;
    1281:   PetscCall(SNESGetKSP(snes, &ksp));
    1282:   PetscCall(KSPSetApplicationContext(ksp, ctx));
    1283:   snes->ctx = ctx;
    1284:   PetscFunctionReturn(PETSC_SUCCESS);
    1285: }

    1287: /*@
    1288:   SNESGetApplicationContext - Gets the user-defined context for the
    1289:   nonlinear solvers set with `SNESGetApplicationContext()` or `SNESSetComputeApplicationContext()`

    1291:   Not Collective

    1293:   Input Parameter:
    1294: . snes - `SNES` context

    1296:   Output Parameter:
    1297: . ctx - user context

    1299:   Level: intermediate

    1301:   Fortran Notes:
    1302:   This only works when the context is a Fortran derived type (it cannot be a `PetscObject`) and you **must** write a Fortran interface definition for this
    1303:   function that tells the Fortran compiler the derived data type that is returned as the `ctx` argument. For example,
    1304: .vb
    1305:   Interface SNESGetApplicationContext
    1306:     Subroutine SNESGetApplicationContext(snes,ctx,ierr)
    1307:   #include <petsc/finclude/petscsnes.h>
    1308:       use petscsnes
    1309:       SNES snes
    1310:       type(tUsertype), pointer :: ctx
    1311:       PetscErrorCode ierr
    1312:     End Subroutine
    1313:   End Interface SNESGetApplicationContext
    1314: .ve

    1316:   The prototype for `ctx` must be
    1317: .vb
    1318:   type(tUsertype), pointer :: ctx
    1319: .ve

    1321: .seealso: [](ch_snes), `SNESSetApplicationContext()`, `SNESSetComputeApplicationContext()`
    1322: @*/
    1323: PetscErrorCode SNESGetApplicationContext(SNES snes, PeCtx ctx)
    1324: {
    1325:   PetscFunctionBegin;
    1327:   *(void **)ctx = snes->ctx;
    1328:   PetscFunctionReturn(PETSC_SUCCESS);
    1329: }

    1331: /*@
    1332:   SNESSetUseMatrixFree - indicates that `SNES` should use matrix-free finite difference matrix-vector products to apply the Jacobian.

    1334:   Logically Collective

    1336:   Input Parameters:
    1337: + snes        - `SNES` context
    1338: . mf_operator - use matrix-free only for the Amat used by `SNESSetJacobian()`, this means the user provided Pmat will continue to be used
    1339: - mf          - use matrix-free for both the Amat and Pmat used by `SNESSetJacobian()`, both the Amat and Pmat set in `SNESSetJacobian()` will be ignored. With
    1340:                 this option no matrix-element based preconditioners can be used in the linear solve since the matrix won't be explicitly available

    1342:   Options Database Keys:
    1343: + -snes_mf_operator - use matrix-free only for the mat operator
    1344: . -snes_mf          - use matrix-free for both the mat and pmat operator
    1345: . -snes_fd_color    - compute the Jacobian via coloring and finite differences.
    1346: - -snes_fd          - compute the Jacobian via finite differences (slow)

    1348:   Level: intermediate

    1350:   Note:
    1351:   `SNES` supports three approaches for computing (approximate) Jacobians: user provided via `SNESSetJacobian()`, matrix-free using `MatCreateSNESMF()`,
    1352:   and computing explicitly with
    1353:   finite differences and coloring using `MatFDColoring`. It is also possible to use automatic differentiation and the `MatFDColoring` object.

    1355: .seealso: [](ch_snes), `SNES`, `SNESGetUseMatrixFree()`, `MatCreateSNESMF()`, `SNESComputeJacobianDefaultColor()`, `MatFDColoring`
    1356: @*/
    1357: PetscErrorCode SNESSetUseMatrixFree(SNES snes, PetscBool mf_operator, PetscBool mf)
    1358: {
    1359:   PetscFunctionBegin;
    1363:   snes->mf          = mf_operator ? PETSC_TRUE : mf;
    1364:   snes->mf_operator = mf_operator;
    1365:   PetscFunctionReturn(PETSC_SUCCESS);
    1366: }

    1368: /*@
    1369:   SNESGetUseMatrixFree - indicates if the `SNES` uses matrix-free finite difference matrix vector products to apply the Jacobian.

    1371:   Not Collective, but the resulting flags will be the same on all MPI processes

    1373:   Input Parameter:
    1374: . snes - `SNES` context

    1376:   Output Parameters:
    1377: + mf_operator - use matrix-free only for the Amat used by `SNESSetJacobian()`, this means the user provided Pmat will continue to be used
    1378: - mf          - use matrix-free for both the Amat and Pmat used by `SNESSetJacobian()`, both the Amat and Pmat set in `SNESSetJacobian()` will be ignored

    1380:   Level: intermediate

    1382: .seealso: [](ch_snes), `SNES`, `SNESSetUseMatrixFree()`, `MatCreateSNESMF()`
    1383: @*/
    1384: PetscErrorCode SNESGetUseMatrixFree(SNES snes, PetscBool *mf_operator, PetscBool *mf)
    1385: {
    1386:   PetscFunctionBegin;
    1388:   if (mf) *mf = snes->mf;
    1389:   if (mf_operator) *mf_operator = snes->mf_operator;
    1390:   PetscFunctionReturn(PETSC_SUCCESS);
    1391: }

    1393: /*@
    1394:   SNESGetIterationNumber - Gets the number of nonlinear iterations completed in the current or most recent `SNESSolve()`

    1396:   Not Collective

    1398:   Input Parameter:
    1399: . snes - `SNES` context

    1401:   Output Parameter:
    1402: . iter - iteration number

    1404:   Level: intermediate

    1406:   Notes:
    1407:   For example, during the computation of iteration 2 this would return 1.

    1409:   This is useful for using lagged Jacobians (where one does not recompute the
    1410:   Jacobian at each `SNES` iteration). For example, the code
    1411: .vb
    1412:       ierr = SNESGetIterationNumber(snes,&it);
    1413:       if (!(it % 2)) {
    1414:         [compute Jacobian here]
    1415:       }
    1416: .ve
    1417:   can be used in your function that computes the Jacobian to cause the Jacobian to be
    1418:   recomputed every second `SNES` iteration. See also `SNESSetLagJacobian()`

    1420:   After the `SNES` solve is complete this will return the number of nonlinear iterations used.

    1422: .seealso: [](ch_snes), `SNES`, `SNESSolve()`, `SNESSetLagJacobian()`, `SNESGetLinearSolveIterations()`, `SNESSetMonitor()`
    1423: @*/
    1424: PetscErrorCode SNESGetIterationNumber(SNES snes, PetscInt *iter)
    1425: {
    1426:   PetscFunctionBegin;
    1428:   PetscAssertPointer(iter, 2);
    1429:   *iter = snes->iter;
    1430:   PetscFunctionReturn(PETSC_SUCCESS);
    1431: }

    1433: /*@
    1434:   SNESSetIterationNumber - Sets the current iteration number.

    1436:   Not Collective

    1438:   Input Parameters:
    1439: + snes - `SNES` context
    1440: - iter - iteration number

    1442:   Level: developer

    1444:   Note:
    1445:   This should only be called inside a `SNES` nonlinear solver.

    1447: .seealso: [](ch_snes), `SNESGetLinearSolveIterations()`
    1448: @*/
    1449: PetscErrorCode SNESSetIterationNumber(SNES snes, PetscInt iter)
    1450: {
    1451:   PetscFunctionBegin;
    1453:   PetscCall(PetscObjectSAWsTakeAccess((PetscObject)snes));
    1454:   snes->iter = iter;
    1455:   PetscCall(PetscObjectSAWsGrantAccess((PetscObject)snes));
    1456:   PetscFunctionReturn(PETSC_SUCCESS);
    1457: }

    1459: /*@
    1460:   SNESGetNonlinearStepFailures - Gets the number of unsuccessful steps
    1461:   attempted by the nonlinear solver in the current or most recent `SNESSolve()` .

    1463:   Not Collective

    1465:   Input Parameter:
    1466: . snes - `SNES` context

    1468:   Output Parameter:
    1469: . nfails - number of unsuccessful steps attempted

    1471:   Level: intermediate

    1473:   Note:
    1474:   This counter is reset to zero for each successive call to `SNESSolve()`.

    1476: .seealso: [](ch_snes), `SNES`, `SNESGetMaxLinearSolveFailures()`, `SNESGetLinearSolveIterations()`, `SNESSetMaxLinearSolveFailures()`, `SNESGetLinearSolveFailures()`,
    1477:           `SNESSetMaxNonlinearStepFailures()`, `SNESGetMaxNonlinearStepFailures()`
    1478: @*/
    1479: PetscErrorCode SNESGetNonlinearStepFailures(SNES snes, PetscInt *nfails)
    1480: {
    1481:   PetscFunctionBegin;
    1483:   PetscAssertPointer(nfails, 2);
    1484:   *nfails = snes->numFailures;
    1485:   PetscFunctionReturn(PETSC_SUCCESS);
    1486: }

    1488: /*@
    1489:   SNESSetMaxNonlinearStepFailures - Sets the maximum number of unsuccessful steps
    1490:   attempted by the nonlinear solver before it gives up and returns unconverged or generates an error

    1492:   Not Collective

    1494:   Input Parameters:
    1495: + snes     - `SNES` context
    1496: - maxFails - maximum of unsuccessful steps allowed, use `PETSC_UNLIMITED` to have no limit on the number of failures

    1498:   Options Database Key:
    1499: . -snes_max_fail <n> - maximum number of unsuccessful steps allowed

    1501:   Level: intermediate

    1503:   Developer Note:
    1504:   The options database key is wrong for this function name

    1506: .seealso: [](ch_snes), `SNESSetErrorIfNotConverged()`, `SNESGetMaxLinearSolveFailures()`, `SNESGetLinearSolveIterations()`, `SNESSetMaxLinearSolveFailures()`, `SNESGetLinearSolveFailures()`,
    1507:           `SNESGetMaxNonlinearStepFailures()`, `SNESGetNonlinearStepFailures()`
    1508: @*/
    1509: PetscErrorCode SNESSetMaxNonlinearStepFailures(SNES snes, PetscInt maxFails)
    1510: {
    1511:   PetscFunctionBegin;

    1514:   if (maxFails == PETSC_UNLIMITED) {
    1515:     snes->maxFailures = PETSC_INT_MAX;
    1516:   } else {
    1517:     PetscCheck(maxFails >= 0, PetscObjectComm((PetscObject)snes), PETSC_ERR_ARG_OUTOFRANGE, "Cannot have a negative maximum number of failures");
    1518:     snes->maxFailures = maxFails;
    1519:   }
    1520:   PetscFunctionReturn(PETSC_SUCCESS);
    1521: }

    1523: /*@
    1524:   SNESGetMaxNonlinearStepFailures - Gets the maximum number of unsuccessful steps
    1525:   attempted by the nonlinear solver before it gives up and returns unconverged or generates an error

    1527:   Not Collective

    1529:   Input Parameter:
    1530: . snes - `SNES` context

    1532:   Output Parameter:
    1533: . maxFails - maximum of unsuccessful steps

    1535:   Level: intermediate

    1537: .seealso: [](ch_snes), `SNESSetErrorIfNotConverged()`, `SNESGetMaxLinearSolveFailures()`, `SNESGetLinearSolveIterations()`, `SNESSetMaxLinearSolveFailures()`, `SNESGetLinearSolveFailures()`,
    1538:           `SNESSetMaxNonlinearStepFailures()`, `SNESGetNonlinearStepFailures()`
    1539: @*/
    1540: PetscErrorCode SNESGetMaxNonlinearStepFailures(SNES snes, PetscInt *maxFails)
    1541: {
    1542:   PetscFunctionBegin;
    1544:   PetscAssertPointer(maxFails, 2);
    1545:   *maxFails = snes->maxFailures;
    1546:   PetscFunctionReturn(PETSC_SUCCESS);
    1547: }

    1549: /*@
    1550:   SNESGetNumberFunctionEvals - Gets the number of user provided function evaluations
    1551:   done by the `SNES` object in the current or most recent `SNESSolve()`

    1553:   Not Collective

    1555:   Input Parameter:
    1556: . snes - `SNES` context

    1558:   Output Parameter:
    1559: . nfuncs - number of evaluations

    1561:   Level: intermediate

    1563:   Note:
    1564:   Reset every time `SNESSolve()` is called unless `SNESSetCountersReset()` is used.

    1566: .seealso: [](ch_snes), `SNES`, `SNESGetMaxLinearSolveFailures()`, `SNESGetLinearSolveIterations()`, `SNESSetMaxLinearSolveFailures()`, `SNESGetLinearSolveFailures()`, `SNESSetCountersReset()`
    1567: @*/
    1568: PetscErrorCode SNESGetNumberFunctionEvals(SNES snes, PetscInt *nfuncs)
    1569: {
    1570:   PetscFunctionBegin;
    1572:   PetscAssertPointer(nfuncs, 2);
    1573:   *nfuncs = snes->nfuncs;
    1574:   PetscFunctionReturn(PETSC_SUCCESS);
    1575: }

    1577: /*@
    1578:   SNESGetLinearSolveFailures - Gets the number of failed (non-converged)
    1579:   linear solvers in the current or most recent `SNESSolve()`

    1581:   Not Collective

    1583:   Input Parameter:
    1584: . snes - `SNES` context

    1586:   Output Parameter:
    1587: . nfails - number of failed solves

    1589:   Options Database Key:
    1590: . -snes_max_linear_solve_fail <num> - The number of failures before the solve is terminated

    1592:   Level: intermediate

    1594:   Note:
    1595:   This counter is reset to zero for each successive call to `SNESSolve()`.

    1597: .seealso: [](ch_snes), `SNESGetMaxLinearSolveFailures()`, `SNESGetLinearSolveIterations()`, `SNESSetMaxLinearSolveFailures()`
    1598: @*/
    1599: PetscErrorCode SNESGetLinearSolveFailures(SNES snes, PetscInt *nfails)
    1600: {
    1601:   PetscFunctionBegin;
    1603:   PetscAssertPointer(nfails, 2);
    1604:   *nfails = snes->numLinearSolveFailures;
    1605:   PetscFunctionReturn(PETSC_SUCCESS);
    1606: }

    1608: /*@
    1609:   SNESSetMaxLinearSolveFailures - the number of failed linear solve attempts
    1610:   allowed before `SNES` returns with a diverged reason of `SNES_DIVERGED_LINEAR_SOLVE`

    1612:   Logically Collective

    1614:   Input Parameters:
    1615: + snes     - `SNES` context
    1616: - maxFails - maximum allowed linear solve failures, use `PETSC_UNLIMITED` to have no limit on the number of failures

    1618:   Options Database Key:
    1619: . -snes_max_linear_solve_fail <num> - The number of failures before the solve is terminated

    1621:   Level: intermediate

    1623:   Note:
    1624:   By default this is 0; that is `SNES` returns on the first failed linear solve

    1626:   Developer Note:
    1627:   The options database key is wrong for this function name

    1629: .seealso: [](ch_snes), `SNESSetErrorIfNotConverged()`, `SNESGetLinearSolveFailures()`, `SNESGetMaxLinearSolveFailures()`, `SNESGetLinearSolveIterations()`
    1630: @*/
    1631: PetscErrorCode SNESSetMaxLinearSolveFailures(SNES snes, PetscInt maxFails)
    1632: {
    1633:   PetscFunctionBegin;

    1637:   if (maxFails == PETSC_UNLIMITED) {
    1638:     snes->maxLinearSolveFailures = PETSC_INT_MAX;
    1639:   } else {
    1640:     PetscCheck(maxFails >= 0, PetscObjectComm((PetscObject)snes), PETSC_ERR_ARG_OUTOFRANGE, "Cannot have a negative maximum number of failures");
    1641:     snes->maxLinearSolveFailures = maxFails;
    1642:   }
    1643:   PetscFunctionReturn(PETSC_SUCCESS);
    1644: }

    1646: /*@
    1647:   SNESGetMaxLinearSolveFailures - gets the maximum number of linear solve failures that
    1648:   are allowed before `SNES` returns as unsuccessful

    1650:   Not Collective

    1652:   Input Parameter:
    1653: . snes - `SNES` context

    1655:   Output Parameter:
    1656: . maxFails - maximum of unsuccessful solves allowed

    1658:   Level: intermediate

    1660:   Note:
    1661:   By default this is 1; that is `SNES` returns on the first failed linear solve

    1663: .seealso: [](ch_snes), `SNESSetErrorIfNotConverged()`, `SNESGetLinearSolveFailures()`, `SNESGetLinearSolveIterations()`, `SNESSetMaxLinearSolveFailures()`,
    1664: @*/
    1665: PetscErrorCode SNESGetMaxLinearSolveFailures(SNES snes, PetscInt *maxFails)
    1666: {
    1667:   PetscFunctionBegin;
    1669:   PetscAssertPointer(maxFails, 2);
    1670:   *maxFails = snes->maxLinearSolveFailures;
    1671:   PetscFunctionReturn(PETSC_SUCCESS);
    1672: }

    1674: /*@
    1675:   SNESGetLinearSolveIterations - Gets the total number of linear iterations
    1676:   used by the nonlinear solver in the most recent `SNESSolve()`

    1678:   Not Collective

    1680:   Input Parameter:
    1681: . snes - `SNES` context

    1683:   Output Parameter:
    1684: . lits - number of linear iterations

    1686:   Level: intermediate

    1688:   Notes:
    1689:   This counter is reset to zero for each successive call to `SNESSolve()` unless `SNESSetCountersReset()` is used.

    1691:   If the linear solver fails inside the `SNESSolve()` the iterations for that call to the linear solver are not included. If you wish to count them
    1692:   then call `KSPGetIterationNumber()` after the failed solve.

    1694: .seealso: [](ch_snes), `SNES`, `SNESGetIterationNumber()`, `SNESGetLinearSolveFailures()`, `SNESGetMaxLinearSolveFailures()`, `SNESSetCountersReset()`
    1695: @*/
    1696: PetscErrorCode SNESGetLinearSolveIterations(SNES snes, PetscInt *lits)
    1697: {
    1698:   PetscFunctionBegin;
    1700:   PetscAssertPointer(lits, 2);
    1701:   *lits = snes->linear_its;
    1702:   PetscFunctionReturn(PETSC_SUCCESS);
    1703: }

    1705: /*@
    1706:   SNESSetCountersReset - Sets whether or not the counters for linear iterations and function evaluations
    1707:   are reset every time `SNESSolve()` is called.

    1709:   Logically Collective

    1711:   Input Parameters:
    1712: + snes  - `SNES` context
    1713: - reset - whether to reset the counters or not, defaults to `PETSC_TRUE`

    1715:   Level: developer

    1717: .seealso: [](ch_snes), `SNESGetNumberFunctionEvals()`, `SNESGetLinearSolveIterations()`, `SNESGetNPC()`
    1718: @*/
    1719: PetscErrorCode SNESSetCountersReset(SNES snes, PetscBool reset)
    1720: {
    1721:   PetscFunctionBegin;
    1724:   snes->counters_reset = reset;
    1725:   PetscFunctionReturn(PETSC_SUCCESS);
    1726: }

    1728: /*@
    1729:   SNESResetCounters - Reset counters for linear iterations and function evaluations.

    1731:   Logically Collective

    1733:   Input Parameters:
    1734: . snes - `SNES` context

    1736:   Level: developer

    1738:   Note:
    1739:   It honors the flag set with `SNESSetCountersReset()`

    1741: .seealso: [](ch_snes), `SNESGetNumberFunctionEvals()`, `SNESGetLinearSolveIterations()`, `SNESGetNPC()`
    1742: @*/
    1743: PetscErrorCode SNESResetCounters(SNES snes)
    1744: {
    1745:   PetscFunctionBegin;
    1747:   if (snes->counters_reset) {
    1748:     snes->nfuncs      = 0;
    1749:     snes->linear_its  = 0;
    1750:     snes->numFailures = 0;
    1751:   }
    1752:   PetscFunctionReturn(PETSC_SUCCESS);
    1753: }

    1755: /*@
    1756:   SNESSetKSP - Sets a `KSP` context for the `SNES` object to use

    1758:   Not Collective, but the `SNES` and `KSP` objects must live on the same `MPI_Comm`

    1760:   Input Parameters:
    1761: + snes - the `SNES` context
    1762: - ksp  - the `KSP` context

    1764:   Level: developer

    1766:   Notes:
    1767:   The `SNES` object already has its `KSP` object, you can obtain with `SNESGetKSP()`
    1768:   so this routine is rarely needed.

    1770:   The `KSP` object that is already in the `SNES` object has its reference count
    1771:   decreased by one when this is called.

    1773: .seealso: [](ch_snes), `SNES`, `KSP`, `KSPGetPC()`, `SNESCreate()`, `KSPCreate()`
    1774: @*/
    1775: PetscErrorCode SNESSetKSP(SNES snes, KSP ksp)
    1776: {
    1777:   PetscFunctionBegin;
    1780:   PetscCheckSameComm(snes, 1, ksp, 2);
    1781:   PetscCall(PetscObjectReference((PetscObject)ksp));
    1782:   if (snes->ksp) PetscCall(PetscObjectDereference((PetscObject)snes->ksp));
    1783:   snes->ksp = ksp;
    1784:   PetscFunctionReturn(PETSC_SUCCESS);
    1785: }

    1787: /*@
    1788:   SNESParametersInitialize - Sets all the parameters in `snes` to their default value (when `SNESCreate()` was called) if they
    1789:   currently contain default values

    1791:   Collective

    1793:   Input Parameter:
    1794: . snes - the `SNES` object

    1796:   Level: developer

    1798:   Developer Note:
    1799:   This is called by all the `SNESCreate_XXX()` routines.

    1801: .seealso: [](ch_snes), `SNES`, `SNESSolve()`, `SNESDestroy()`, `SNESSetLagPreconditioner()`, `SNESSetLagJacobian()`,
    1802:           `PetscObjectParameterSetDefault()`
    1803: @*/
    1804: PetscErrorCode SNESParametersInitialize(SNES snes)
    1805: {
    1806:   PetscObjectParameterSetDefault(snes, max_its, 50);
    1807:   PetscObjectParameterSetDefault(snes, max_funcs, 10000);
    1808:   PetscObjectParameterSetDefault(snes, rtol, PetscDefined(USE_REAL_SINGLE) ? 1.e-5 : 1.e-8);
    1809:   PetscObjectParameterSetDefault(snes, abstol, PetscDefined(USE_REAL_SINGLE) ? 1.e-25 : 1.e-50);
    1810:   PetscObjectParameterSetDefault(snes, stol, PetscDefined(USE_REAL_SINGLE) ? 1.e-5 : 1.e-8);
    1811:   PetscObjectParameterSetDefault(snes, divtol, 1.e4);
    1812:   return PETSC_SUCCESS;
    1813: }

    1815: /*@
    1816:   SNESCreate - Creates a nonlinear solver context used to manage a set of nonlinear solves

    1818:   Collective

    1820:   Input Parameter:
    1821: . comm - MPI communicator

    1823:   Output Parameter:
    1824: . outsnes - the new `SNES` context

    1826:   Options Database Keys:
    1827: + -snes_mf          - Activates default matrix-free Jacobian-vector products, and no matrix to construct a preconditioner
    1828: . -snes_mf_operator - Activates default matrix-free Jacobian-vector products, and a user-provided matrix as set by `SNESSetJacobian()`
    1829: . -snes_fd_coloring - uses a relative fast computation of the Jacobian using finite differences and a graph coloring
    1830: - -snes_fd          - Uses (slow!) finite differences to compute Jacobian

    1832:   Level: beginner

    1834:   Developer Notes:
    1835:   `SNES` always creates a `KSP` object even though many `SNES` methods do not use it. This is
    1836:   unfortunate and should be fixed at some point. The flag snes->usesksp indicates if the
    1837:   particular method does use `KSP` and regulates if the information about the `KSP` is printed
    1838:   in `SNESView()`.

    1840:   `TSSetFromOptions()` does call `SNESSetFromOptions()` which can lead to users being confused
    1841:   by help messages about meaningless `SNES` options.

    1843:   `SNES` always creates the `snes->kspconvctx` even though it is used by only one type. This should be fixed.

    1845: .seealso: [](ch_snes), `SNES`, `SNESSolve()`, `SNESDestroy()`, `SNESSetLagPreconditioner()`, `SNESSetLagJacobian()`
    1846: @*/
    1847: PetscErrorCode SNESCreate(MPI_Comm comm, SNES *outsnes)
    1848: {
    1849:   SNES       snes;
    1850:   SNESKSPEW *kctx;

    1852:   PetscFunctionBegin;
    1853:   PetscAssertPointer(outsnes, 2);
    1854:   PetscCall(SNESInitializePackage());

    1856:   PetscCall(PetscHeaderCreate(snes, SNES_CLASSID, "SNES", "Nonlinear solver", "SNES", comm, SNESDestroy, SNESView));
    1857:   snes->ops->converged = SNESConvergedDefault;
    1858:   snes->usesksp        = PETSC_TRUE;
    1859:   snes->norm           = 0.0;
    1860:   snes->xnorm          = 0.0;
    1861:   snes->ynorm          = 0.0;
    1862:   snes->normschedule   = SNES_NORM_ALWAYS;
    1863:   snes->functype       = SNES_FUNCTION_DEFAULT;
    1864:   snes->ttol           = 0.0;

    1866:   snes->rnorm0               = 0;
    1867:   snes->nfuncs               = 0;
    1868:   snes->numFailures          = 0;
    1869:   snes->maxFailures          = 1;
    1870:   snes->linear_its           = 0;
    1871:   snes->lagjacobian          = 1;
    1872:   snes->jac_iter             = 0;
    1873:   snes->lagjac_persist       = PETSC_FALSE;
    1874:   snes->lagpreconditioner    = 1;
    1875:   snes->pre_iter             = 0;
    1876:   snes->lagpre_persist       = PETSC_FALSE;
    1877:   snes->numbermonitors       = 0;
    1878:   snes->numberreasonviews    = 0;
    1879:   snes->data                 = NULL;
    1880:   snes->setupcalled          = PETSC_FALSE;
    1881:   snes->ksp_ewconv           = PETSC_FALSE;
    1882:   snes->nwork                = 0;
    1883:   snes->work                 = NULL;
    1884:   snes->nvwork               = 0;
    1885:   snes->vwork                = NULL;
    1886:   snes->conv_hist_len        = 0;
    1887:   snes->conv_hist_max        = 0;
    1888:   snes->conv_hist            = NULL;
    1889:   snes->conv_hist_its        = NULL;
    1890:   snes->conv_hist_reset      = PETSC_TRUE;
    1891:   snes->counters_reset       = PETSC_TRUE;
    1892:   snes->vec_func_init_set    = PETSC_FALSE;
    1893:   snes->reason               = SNES_CONVERGED_ITERATING;
    1894:   snes->npcside              = PC_RIGHT;
    1895:   snes->setfromoptionscalled = 0;

    1897:   snes->mf          = PETSC_FALSE;
    1898:   snes->mf_operator = PETSC_FALSE;
    1899:   snes->mf_version  = 1;

    1901:   snes->numLinearSolveFailures = 0;
    1902:   snes->maxLinearSolveFailures = 1;

    1904:   snes->vizerotolerance     = 1.e-8;
    1905:   snes->checkjacdomainerror = PetscDefined(USE_DEBUG) ? PETSC_TRUE : PETSC_FALSE;

    1907:   /* Set this to true if the implementation of SNESSolve_XXX does compute the residual at the final solution. */
    1908:   snes->alwayscomputesfinalresidual = PETSC_FALSE;

    1910:   /* Create context to compute Eisenstat-Walker relative tolerance for KSP */
    1911:   PetscCall(PetscNew(&kctx));

    1913:   snes->kspconvctx  = kctx;
    1914:   kctx->version     = 2;
    1915:   kctx->rtol_0      = 0.3; /* Eisenstat and Walker suggest rtol_0=.5, but
    1916:                              this was too large for some test cases */
    1917:   kctx->rtol_last   = 0.0;
    1918:   kctx->rtol_max    = 0.9;
    1919:   kctx->gamma       = 1.0;
    1920:   kctx->alpha       = 0.5 * (1.0 + PetscSqrtReal(5.0));
    1921:   kctx->alpha2      = kctx->alpha;
    1922:   kctx->threshold   = 0.1;
    1923:   kctx->lresid_last = 0.0;
    1924:   kctx->norm_last   = 0.0;

    1926:   kctx->rk_last     = 0.0;
    1927:   kctx->rk_last_2   = 0.0;
    1928:   kctx->rtol_last_2 = 0.0;
    1929:   kctx->v4_p1       = 0.1;
    1930:   kctx->v4_p2       = 0.4;
    1931:   kctx->v4_p3       = 0.7;
    1932:   kctx->v4_m1       = 0.8;
    1933:   kctx->v4_m2       = 0.5;
    1934:   kctx->v4_m3       = 0.1;
    1935:   kctx->v4_m4       = 0.5;

    1937:   PetscCall(SNESParametersInitialize(snes));
    1938:   *outsnes = snes;
    1939:   PetscFunctionReturn(PETSC_SUCCESS);
    1940: }

    1942: /*@C
    1943:   SNESSetFunction - Sets the function evaluation routine and function
    1944:   vector for use by the `SNES` routines in solving systems of nonlinear
    1945:   equations.

    1947:   Logically Collective

    1949:   Input Parameters:
    1950: + snes - the `SNES` context
    1951: . r    - vector to store function values, may be `NULL`
    1952: . f    - function evaluation routine;  for calling sequence see `SNESFunctionFn`
    1953: - ctx  - [optional] user-defined context for private data for the
    1954:          function evaluation routine (may be `NULL`)

    1956:   Level: beginner

    1958: .seealso: [](ch_snes), `SNES`, `SNESGetFunction()`, `SNESComputeFunction()`, `SNESSetJacobian()`, `SNESSetPicard()`, `SNESFunctionFn`
    1959: @*/
    1960: PetscErrorCode SNESSetFunction(SNES snes, Vec r, SNESFunctionFn *f, void *ctx)
    1961: {
    1962:   DM dm;

    1964:   PetscFunctionBegin;
    1966:   if (r) {
    1968:     PetscCheckSameComm(snes, 1, r, 2);
    1969:     PetscCall(PetscObjectReference((PetscObject)r));
    1970:     PetscCall(VecDestroy(&snes->vec_func));
    1971:     snes->vec_func = r;
    1972:   }
    1973:   PetscCall(SNESGetDM(snes, &dm));
    1974:   PetscCall(DMSNESSetFunction(dm, f, ctx));
    1975:   if (f == SNESPicardComputeFunction) PetscCall(DMSNESSetMFFunction(dm, SNESPicardComputeMFFunction, ctx));
    1976:   PetscFunctionReturn(PETSC_SUCCESS);
    1977: }

    1979: /*@C
    1980:   SNESSetInitialFunction - Set an already computed function evaluation at the initial guess to be reused by `SNESSolve()`.

    1982:   Logically Collective

    1984:   Input Parameters:
    1985: + snes - the `SNES` context
    1986: - f    - vector to store function value

    1988:   Level: developer

    1990:   Notes:
    1991:   This should not be modified during the solution procedure.

    1993:   This is used extensively in the `SNESFAS` hierarchy and in nonlinear preconditioning.

    1995: .seealso: [](ch_snes), `SNES`, `SNESFAS`, `SNESSetFunction()`, `SNESComputeFunction()`, `SNESSetInitialFunctionNorm()`
    1996: @*/
    1997: PetscErrorCode SNESSetInitialFunction(SNES snes, Vec f)
    1998: {
    1999:   Vec vec_func;

    2001:   PetscFunctionBegin;
    2004:   PetscCheckSameComm(snes, 1, f, 2);
    2005:   if (snes->npcside == PC_LEFT && snes->functype == SNES_FUNCTION_PRECONDITIONED) {
    2006:     snes->vec_func_init_set = PETSC_FALSE;
    2007:     PetscFunctionReturn(PETSC_SUCCESS);
    2008:   }
    2009:   PetscCall(SNESGetFunction(snes, &vec_func, NULL, NULL));
    2010:   PetscCall(VecCopy(f, vec_func));

    2012:   snes->vec_func_init_set = PETSC_TRUE;
    2013:   PetscFunctionReturn(PETSC_SUCCESS);
    2014: }

    2016: /*@
    2017:   SNESSetNormSchedule - Sets the `SNESNormSchedule` used in convergence and monitoring
    2018:   of the `SNES` method, when norms are computed in the solving process

    2020:   Logically Collective

    2022:   Input Parameters:
    2023: + snes         - the `SNES` context
    2024: - normschedule - the frequency of norm computation

    2026:   Options Database Key:
    2027: . -snes_norm_schedule <none, always, initialonly, finalonly, initialfinalonly> - set the schedule

    2029:   Level: advanced

    2031:   Notes:
    2032:   Only certain `SNES` methods support certain `SNESNormSchedules`.  Most require evaluation
    2033:   of the nonlinear function and the taking of its norm at every iteration to
    2034:   even ensure convergence at all.  However, methods such as custom Gauss-Seidel methods
    2035:   `SNESNGS` and the like do not require the norm of the function to be computed, and therefore
    2036:   may either be monitored for convergence or not.  As these are often used as nonlinear
    2037:   preconditioners, monitoring the norm of their error is not a useful enterprise within
    2038:   their solution.

    2040: .seealso: [](ch_snes), `SNESNormSchedule`, `SNESGetNormSchedule()`, `SNESComputeFunction()`, `VecNorm()`, `SNESSetFunction()`, `SNESSetInitialFunction()`
    2041: @*/
    2042: PetscErrorCode SNESSetNormSchedule(SNES snes, SNESNormSchedule normschedule)
    2043: {
    2044:   PetscFunctionBegin;
    2046:   snes->normschedule = normschedule;
    2047:   PetscFunctionReturn(PETSC_SUCCESS);
    2048: }

    2050: /*@
    2051:   SNESGetNormSchedule - Gets the `SNESNormSchedule` used in convergence and monitoring
    2052:   of the `SNES` method.

    2054:   Logically Collective

    2056:   Input Parameters:
    2057: + snes         - the `SNES` context
    2058: - normschedule - the type of the norm used

    2060:   Level: advanced

    2062: .seealso: [](ch_snes), `SNES`, `SNESSetNormSchedule()`, `SNESComputeFunction()`, `VecNorm()`, `SNESSetFunction()`, `SNESSetInitialFunction()`, `SNESNormSchedule`
    2063: @*/
    2064: PetscErrorCode SNESGetNormSchedule(SNES snes, SNESNormSchedule *normschedule)
    2065: {
    2066:   PetscFunctionBegin;
    2068:   *normschedule = snes->normschedule;
    2069:   PetscFunctionReturn(PETSC_SUCCESS);
    2070: }

    2072: /*@
    2073:   SNESSetFunctionNorm - Sets the last computed residual norm.

    2075:   Logically Collective

    2077:   Input Parameters:
    2078: + snes - the `SNES` context
    2079: - norm - the value of the norm

    2081:   Level: developer

    2083: .seealso: [](ch_snes), `SNES`, `SNESGetNormSchedule()`, `SNESComputeFunction()`, `VecNorm()`, `SNESSetFunction()`, `SNESSetInitialFunction()`, `SNESNormSchedule`
    2084: @*/
    2085: PetscErrorCode SNESSetFunctionNorm(SNES snes, PetscReal norm)
    2086: {
    2087:   PetscFunctionBegin;
    2089:   snes->norm = norm;
    2090:   PetscFunctionReturn(PETSC_SUCCESS);
    2091: }

    2093: /*@
    2094:   SNESGetFunctionNorm - Gets the last computed norm of the residual

    2096:   Not Collective

    2098:   Input Parameter:
    2099: . snes - the `SNES` context

    2101:   Output Parameter:
    2102: . norm - the last computed residual norm

    2104:   Level: developer

    2106: .seealso: [](ch_snes), `SNES`, `SNESSetNormSchedule()`, `SNESComputeFunction()`, `VecNorm()`, `SNESSetFunction()`, `SNESSetInitialFunction()`, `SNESNormSchedule`
    2107: @*/
    2108: PetscErrorCode SNESGetFunctionNorm(SNES snes, PetscReal *norm)
    2109: {
    2110:   PetscFunctionBegin;
    2112:   PetscAssertPointer(norm, 2);
    2113:   *norm = snes->norm;
    2114:   PetscFunctionReturn(PETSC_SUCCESS);
    2115: }

    2117: /*@
    2118:   SNESGetUpdateNorm - Gets the last computed norm of the solution update

    2120:   Not Collective

    2122:   Input Parameter:
    2123: . snes - the `SNES` context

    2125:   Output Parameter:
    2126: . ynorm - the last computed update norm

    2128:   Level: developer

    2130:   Note:
    2131:   The new solution is the current solution plus the update, so this norm is an indication of the size of the update

    2133: .seealso: [](ch_snes), `SNES`, `SNESSetNormSchedule()`, `SNESComputeFunction()`, `SNESGetFunctionNorm()`
    2134: @*/
    2135: PetscErrorCode SNESGetUpdateNorm(SNES snes, PetscReal *ynorm)
    2136: {
    2137:   PetscFunctionBegin;
    2139:   PetscAssertPointer(ynorm, 2);
    2140:   *ynorm = snes->ynorm;
    2141:   PetscFunctionReturn(PETSC_SUCCESS);
    2142: }

    2144: /*@
    2145:   SNESGetSolutionNorm - Gets the last computed norm of the solution

    2147:   Not Collective

    2149:   Input Parameter:
    2150: . snes - the `SNES` context

    2152:   Output Parameter:
    2153: . xnorm - the last computed solution norm

    2155:   Level: developer

    2157: .seealso: [](ch_snes), `SNES`, `SNESSetNormSchedule()`, `SNESComputeFunction()`, `SNESGetFunctionNorm()`, `SNESGetUpdateNorm()`
    2158: @*/
    2159: PetscErrorCode SNESGetSolutionNorm(SNES snes, PetscReal *xnorm)
    2160: {
    2161:   PetscFunctionBegin;
    2163:   PetscAssertPointer(xnorm, 2);
    2164:   *xnorm = snes->xnorm;
    2165:   PetscFunctionReturn(PETSC_SUCCESS);
    2166: }

    2168: /*@
    2169:   SNESSetFunctionType - Sets the `SNESFunctionType`
    2170:   of the `SNES` method.

    2172:   Logically Collective

    2174:   Input Parameters:
    2175: + snes - the `SNES` context
    2176: - type - the function type

    2178:   Level: developer

    2180:   Values of the function type\:
    2181: +  `SNES_FUNCTION_DEFAULT`          - the default for the given `SNESType`
    2182: .  `SNES_FUNCTION_UNPRECONDITIONED` - an unpreconditioned function evaluation (this is the function provided with `SNESSetFunction()`
    2183: -  `SNES_FUNCTION_PRECONDITIONED`   - a transformation of the function provided with `SNESSetFunction()`

    2185:   Note:
    2186:   Different `SNESType`s use this value in different ways

    2188: .seealso: [](ch_snes), `SNES`, `SNESFunctionType`, `SNESGetNormSchedule()`, `SNESComputeFunction()`, `VecNorm()`, `SNESSetFunction()`, `SNESSetInitialFunction()`, `SNESNormSchedule`
    2189: @*/
    2190: PetscErrorCode SNESSetFunctionType(SNES snes, SNESFunctionType type)
    2191: {
    2192:   PetscFunctionBegin;
    2194:   snes->functype = type;
    2195:   PetscFunctionReturn(PETSC_SUCCESS);
    2196: }

    2198: /*@
    2199:   SNESGetFunctionType - Gets the `SNESFunctionType` used in convergence and monitoring set with `SNESSetFunctionType()`
    2200:   of the SNES method.

    2202:   Logically Collective

    2204:   Input Parameters:
    2205: + snes - the `SNES` context
    2206: - type - the type of the function evaluation, see `SNESSetFunctionType()`

    2208:   Level: advanced

    2210: .seealso: [](ch_snes), `SNESSetFunctionType()`, `SNESFunctionType`, `SNESSetNormSchedule()`, `SNESComputeFunction()`, `VecNorm()`, `SNESSetFunction()`, `SNESSetInitialFunction()`, `SNESNormSchedule`
    2211: @*/
    2212: PetscErrorCode SNESGetFunctionType(SNES snes, SNESFunctionType *type)
    2213: {
    2214:   PetscFunctionBegin;
    2216:   *type = snes->functype;
    2217:   PetscFunctionReturn(PETSC_SUCCESS);
    2218: }

    2220: /*@C
    2221:   SNESSetNGS - Sets the user nonlinear Gauss-Seidel routine for
    2222:   use with composed nonlinear solvers.

    2224:   Input Parameters:
    2225: + snes - the `SNES` context, usually of the `SNESType` `SNESNGS`
    2226: . f    - function evaluation routine to apply Gauss-Seidel, see `SNESNGSFn` for calling sequence
    2227: - ctx  - [optional] user-defined context for private data for the smoother evaluation routine (may be `NULL`)

    2229:   Level: intermediate

    2231:   Note:
    2232:   The `SNESNGS` routines are used by the composed nonlinear solver to generate
    2233:   a problem appropriate update to the solution, particularly `SNESFAS`.

    2235: .seealso: [](ch_snes), `SNESNGS`, `SNESGetNGS()`, `SNESNCG`, `SNESGetFunction()`, `SNESComputeNGS()`, `SNESNGSFn`
    2236: @*/
    2237: PetscErrorCode SNESSetNGS(SNES snes, SNESNGSFn *f, void *ctx)
    2238: {
    2239:   DM dm;

    2241:   PetscFunctionBegin;
    2243:   PetscCall(SNESGetDM(snes, &dm));
    2244:   PetscCall(DMSNESSetNGS(dm, f, ctx));
    2245:   PetscFunctionReturn(PETSC_SUCCESS);
    2246: }

    2248: /*
    2249:      This is used for -snes_mf_operator; it uses a duplicate of snes->jacobian_pre because snes->jacobian_pre cannot be
    2250:    changed during the KSPSolve()
    2251: */
    2252: PetscErrorCode SNESPicardComputeMFFunction(SNES snes, Vec x, Vec f, void *ctx)
    2253: {
    2254:   DM     dm;
    2255:   DMSNES sdm;

    2257:   PetscFunctionBegin;
    2258:   PetscCall(SNESGetDM(snes, &dm));
    2259:   PetscCall(DMGetDMSNES(dm, &sdm));
    2260:   /*  A(x)*x - b(x) */
    2261:   if (sdm->ops->computepfunction) {
    2262:     PetscCallBack("SNES Picard callback function", (*sdm->ops->computepfunction)(snes, x, f, sdm->pctx));
    2263:     PetscCall(VecScale(f, -1.0));
    2264:     /* Cannot share nonzero pattern because of the possible use of SNESComputeJacobianDefault() */
    2265:     if (!snes->picard) PetscCall(MatDuplicate(snes->jacobian_pre, MAT_DO_NOT_COPY_VALUES, &snes->picard));
    2266:     PetscCallBack("SNES Picard callback Jacobian", (*sdm->ops->computepjacobian)(snes, x, snes->picard, snes->picard, sdm->pctx));
    2267:     PetscCall(MatMultAdd(snes->picard, x, f, f));
    2268:   } else {
    2269:     PetscCallBack("SNES Picard callback Jacobian", (*sdm->ops->computepjacobian)(snes, x, snes->picard, snes->picard, sdm->pctx));
    2270:     PetscCall(MatMult(snes->picard, x, f));
    2271:   }
    2272:   PetscFunctionReturn(PETSC_SUCCESS);
    2273: }

    2275: PetscErrorCode SNESPicardComputeFunction(SNES snes, Vec x, Vec f, void *ctx)
    2276: {
    2277:   DM     dm;
    2278:   DMSNES sdm;

    2280:   PetscFunctionBegin;
    2281:   PetscCall(SNESGetDM(snes, &dm));
    2282:   PetscCall(DMGetDMSNES(dm, &sdm));
    2283:   /*  A(x)*x - b(x) */
    2284:   if (sdm->ops->computepfunction) {
    2285:     PetscCallBack("SNES Picard callback function", (*sdm->ops->computepfunction)(snes, x, f, sdm->pctx));
    2286:     PetscCall(VecScale(f, -1.0));
    2287:     PetscCallBack("SNES Picard callback Jacobian", (*sdm->ops->computepjacobian)(snes, x, snes->jacobian, snes->jacobian_pre, sdm->pctx));
    2288:     PetscCall(MatMultAdd(snes->jacobian_pre, x, f, f));
    2289:   } else {
    2290:     PetscCallBack("SNES Picard callback Jacobian", (*sdm->ops->computepjacobian)(snes, x, snes->jacobian, snes->jacobian_pre, sdm->pctx));
    2291:     PetscCall(MatMult(snes->jacobian_pre, x, f));
    2292:   }
    2293:   PetscFunctionReturn(PETSC_SUCCESS);
    2294: }

    2296: PetscErrorCode SNESPicardComputeJacobian(SNES snes, Vec x1, Mat J, Mat B, void *ctx)
    2297: {
    2298:   PetscFunctionBegin;
    2299:   /* the jacobian matrix should be pre-filled in SNESPicardComputeFunction */
    2300:   /* must assembly if matrix-free to get the last SNES solution */
    2301:   PetscCall(MatAssemblyBegin(J, MAT_FINAL_ASSEMBLY));
    2302:   PetscCall(MatAssemblyEnd(J, MAT_FINAL_ASSEMBLY));
    2303:   PetscFunctionReturn(PETSC_SUCCESS);
    2304: }

    2306: /*@C
    2307:   SNESSetPicard - Use `SNES` to solve the system $A(x) x = bp(x) + b $ via a Picard type iteration (Picard linearization)

    2309:   Logically Collective

    2311:   Input Parameters:
    2312: + snes - the `SNES` context
    2313: . r    - vector to store function values, may be `NULL`
    2314: . bp   - function evaluation routine, may be `NULL`, for the calling sequence see `SNESFunctionFn`
    2315: . Amat - matrix with which $A(x) x - bp(x) - b$ is to be computed
    2316: . Pmat - matrix from which preconditioner is computed (usually the same as `Amat`)
    2317: . J    - function to compute matrix values, for the calling sequence see `SNESJacobianFn`
    2318: - ctx  - [optional] user-defined context for private data for the function evaluation routine (may be `NULL`)

    2320:   Level: intermediate

    2322:   Notes:
    2323:   It is often better to provide the nonlinear function $F()$ and some approximation to its Jacobian directly and use
    2324:   an approximate Newton solver. This interface is provided to allow porting/testing a previous Picard based code in PETSc before converting it to approximate Newton.

    2326:   One can call `SNESSetPicard()` or `SNESSetFunction()` (and possibly `SNESSetJacobian()`) but cannot call both

    2328:   Solves the equation $A(x) x = bp(x) - b$ via the defect correction algorithm $A(x^{n}) (x^{n+1} - x^{n}) = bp(x^{n}) + b - A(x^{n})x^{n}$.
    2329:   When an exact solver is used this corresponds to the "classic" Picard $A(x^{n}) x^{n+1} = bp(x^{n}) + b$ iteration.

    2331:   Run with `-snes_mf_operator` to solve the system with Newton's method using $A(x^{n})$ to construct the preconditioner.

    2333:   We implement the defect correction form of the Picard iteration because it converges much more generally when inexact linear solvers are used then
    2334:   the direct Picard iteration $A(x^n) x^{n+1} = bp(x^n) + b$

    2336:   There is some controversity over the definition of a Picard iteration for nonlinear systems but almost everyone agrees that it involves a linear solve and some
    2337:   believe it is the iteration  $A(x^{n}) x^{n+1} = b(x^{n})$ hence we use the name Picard. If anyone has an authoritative  reference that defines the Picard iteration
    2338:   different please contact us at petsc-dev@mcs.anl.gov and we'll have an entirely new argument \:-).

    2340:   When used with `-snes_mf_operator` this will run matrix-free Newton's method where the matrix-vector product is of the true Jacobian of $A(x)x - bp(x) - b$ and
    2341:   $A(x^{n})$ is used to build the preconditioner

    2343:   When used with `-snes_fd` this will compute the true Jacobian (very slowly one column at a time) and thus represent Newton's method.

    2345:   When used with `-snes_fd_coloring` this will compute the Jacobian via coloring and thus represent a faster implementation of Newton's method. But the
    2346:   the nonzero structure of the Jacobian is, in general larger than that of the Picard matrix $A$ so you must provide in $A$ the needed nonzero structure for the correct
    2347:   coloring. When using `DMDA` this may mean creating the matrix $A$ with `DMCreateMatrix()` using a wider stencil than strictly needed for $A$ or with a `DMDA_STENCIL_BOX`.
    2348:   See the comment in src/snes/tutorials/ex15.c.

    2350: .seealso: [](ch_snes), `SNES`, `SNESGetFunction()`, `SNESSetFunction()`, `SNESComputeFunction()`, `SNESSetJacobian()`, `SNESGetPicard()`, `SNESLineSearchPreCheckPicard()`,
    2351:           `SNESFunctionFn`, `SNESJacobianFn`
    2352: @*/
    2353: PetscErrorCode SNESSetPicard(SNES snes, Vec r, SNESFunctionFn *bp, Mat Amat, Mat Pmat, SNESJacobianFn *J, void *ctx)
    2354: {
    2355:   DM dm;

    2357:   PetscFunctionBegin;
    2359:   PetscCall(SNESGetDM(snes, &dm));
    2360:   PetscCall(DMSNESSetPicard(dm, bp, J, ctx));
    2361:   PetscCall(DMSNESSetMFFunction(dm, SNESPicardComputeMFFunction, ctx));
    2362:   PetscCall(SNESSetFunction(snes, r, SNESPicardComputeFunction, ctx));
    2363:   PetscCall(SNESSetJacobian(snes, Amat, Pmat, SNESPicardComputeJacobian, ctx));
    2364:   PetscFunctionReturn(PETSC_SUCCESS);
    2365: }

    2367: /*@C
    2368:   SNESGetPicard - Returns the context for the Picard iteration

    2370:   Not Collective, but `Vec` is parallel if `SNES` is parallel. Collective if `Vec` is requested, but has not been created yet.

    2372:   Input Parameter:
    2373: . snes - the `SNES` context

    2375:   Output Parameters:
    2376: + r    - the function (or `NULL`)
    2377: . f    - the function (or `NULL`);  for calling sequence see `SNESFunctionFn`
    2378: . Amat - the matrix used to defined the operation A(x) x - b(x) (or `NULL`)
    2379: . Pmat - the matrix from which the preconditioner will be constructed (or `NULL`)
    2380: . J    - the function for matrix evaluation (or `NULL`);  for calling sequence see `SNESJacobianFn`
    2381: - ctx  - the function context (or `NULL`)

    2383:   Level: advanced

    2385: .seealso: [](ch_snes), `SNESSetFunction()`, `SNESSetPicard()`, `SNESGetFunction()`, `SNESGetJacobian()`, `SNESGetDM()`, `SNESFunctionFn`, `SNESJacobianFn`
    2386: @*/
    2387: PetscErrorCode SNESGetPicard(SNES snes, Vec *r, SNESFunctionFn **f, Mat *Amat, Mat *Pmat, SNESJacobianFn **J, void **ctx)
    2388: {
    2389:   DM dm;

    2391:   PetscFunctionBegin;
    2393:   PetscCall(SNESGetFunction(snes, r, NULL, NULL));
    2394:   PetscCall(SNESGetJacobian(snes, Amat, Pmat, NULL, NULL));
    2395:   PetscCall(SNESGetDM(snes, &dm));
    2396:   PetscCall(DMSNESGetPicard(dm, f, J, ctx));
    2397:   PetscFunctionReturn(PETSC_SUCCESS);
    2398: }

    2400: /*@C
    2401:   SNESSetComputeInitialGuess - Sets a routine used to compute an initial guess for the nonlinear problem

    2403:   Logically Collective

    2405:   Input Parameters:
    2406: + snes - the `SNES` context
    2407: . func - function evaluation routine, see `SNESInitialGuessFn` for the calling sequence
    2408: - ctx  - [optional] user-defined context for private data for the
    2409:          function evaluation routine (may be `NULL`)

    2411:   Level: intermediate

    2413: .seealso: [](ch_snes), `SNES`, `SNESSolve()`, `SNESSetFunction()`, `SNESGetFunction()`, `SNESComputeFunction()`, `SNESSetJacobian()`, `SNESInitialGuessFn`
    2414: @*/
    2415: PetscErrorCode SNESSetComputeInitialGuess(SNES snes, SNESInitialGuessFn *func, void *ctx)
    2416: {
    2417:   PetscFunctionBegin;
    2419:   if (func) snes->ops->computeinitialguess = func;
    2420:   if (ctx) snes->initialguessP = ctx;
    2421:   PetscFunctionReturn(PETSC_SUCCESS);
    2422: }

    2424: /*@C
    2425:   SNESGetRhs - Gets the vector for solving F(x) = `rhs`. If `rhs` is not set
    2426:   it assumes a zero right-hand side.

    2428:   Logically Collective

    2430:   Input Parameter:
    2431: . snes - the `SNES` context

    2433:   Output Parameter:
    2434: . rhs - the right-hand side vector or `NULL` if there is no right-hand side vector

    2436:   Level: intermediate

    2438: .seealso: [](ch_snes), `SNES`, `SNESGetSolution()`, `SNESGetFunction()`, `SNESComputeFunction()`, `SNESSetJacobian()`, `SNESSetFunction()`
    2439: @*/
    2440: PetscErrorCode SNESGetRhs(SNES snes, Vec *rhs)
    2441: {
    2442:   PetscFunctionBegin;
    2444:   PetscAssertPointer(rhs, 2);
    2445:   *rhs = snes->vec_rhs;
    2446:   PetscFunctionReturn(PETSC_SUCCESS);
    2447: }

    2449: /*@
    2450:   SNESComputeFunction - Calls the function that has been set with `SNESSetFunction()`.

    2452:   Collective

    2454:   Input Parameters:
    2455: + snes - the `SNES` context
    2456: - x    - input vector

    2458:   Output Parameter:
    2459: . y - function vector, as set by `SNESSetFunction()`

    2461:   Level: developer

    2463:   Notes:
    2464:   `SNESComputeFunction()` is typically used within nonlinear solvers
    2465:   implementations, so users would not generally call this routine themselves.

    2467:   When solving for $F(x) = b$, this routine computes $y = F(x) - b$.

    2469: .seealso: [](ch_snes), `SNES`, `SNESSetFunction()`, `SNESGetFunction()`, `SNESComputeMFFunction()`
    2470: @*/
    2471: PetscErrorCode SNESComputeFunction(SNES snes, Vec x, Vec y)
    2472: {
    2473:   DM     dm;
    2474:   DMSNES sdm;

    2476:   PetscFunctionBegin;
    2480:   PetscCheckSameComm(snes, 1, x, 2);
    2481:   PetscCheckSameComm(snes, 1, y, 3);
    2482:   PetscCall(VecValidValues_Internal(x, 2, PETSC_TRUE));

    2484:   PetscCall(SNESGetDM(snes, &dm));
    2485:   PetscCall(DMGetDMSNES(dm, &sdm));
    2486:   PetscCheck(sdm->ops->computefunction || snes->vec_rhs, PETSC_COMM_SELF, PETSC_ERR_ARG_WRONGSTATE, "Must call SNESSetFunction() or SNESSetDM() before SNESComputeFunction(), likely called from SNESSolve().");
    2487:   if (sdm->ops->computefunction) {
    2488:     if (sdm->ops->computefunction != SNESObjectiveComputeFunctionDefaultFD) PetscCall(PetscLogEventBegin(SNES_FunctionEval, snes, x, y, 0));
    2489:     PetscCall(VecLockReadPush(x));
    2490:     /* ensure domainerror is false prior to computefunction evaluation (may not have been reset) */
    2491:     snes->domainerror = PETSC_FALSE;
    2492:     {
    2493:       void           *ctx;
    2494:       SNESFunctionFn *computefunction;
    2495:       PetscCall(DMSNESGetFunction(dm, &computefunction, &ctx));
    2496:       PetscCallBack("SNES callback function", (*computefunction)(snes, x, y, ctx));
    2497:     }
    2498:     PetscCall(VecLockReadPop(x));
    2499:     if (sdm->ops->computefunction != SNESObjectiveComputeFunctionDefaultFD) PetscCall(PetscLogEventEnd(SNES_FunctionEval, snes, x, y, 0));
    2500:   } else /* if (snes->vec_rhs) */ {
    2501:     PetscCall(MatMult(snes->jacobian, x, y));
    2502:   }
    2503:   if (snes->vec_rhs) PetscCall(VecAXPY(y, -1.0, snes->vec_rhs));
    2504:   snes->nfuncs++;
    2505:   /*
    2506:      domainerror might not be set on all processes; so we tag vector locally with Inf and the next inner product or norm will
    2507:      propagate the value to all processes
    2508:   */
    2509:   PetscCall(VecFlag(y, snes->domainerror));
    2510:   PetscFunctionReturn(PETSC_SUCCESS);
    2511: }

    2513: /*@
    2514:   SNESComputeMFFunction - Calls the function that has been set with `DMSNESSetMFFunction()`.

    2516:   Collective

    2518:   Input Parameters:
    2519: + snes - the `SNES` context
    2520: - x    - input vector

    2522:   Output Parameter:
    2523: . y - output vector

    2525:   Level: developer

    2527:   Notes:
    2528:   `SNESComputeMFFunction()` is used within the matrix-vector products called by the matrix created with `MatCreateSNESMF()`
    2529:   so users would not generally call this routine themselves.

    2531:   Since this function is intended for use with finite differencing it does not subtract the right-hand side vector provided with `SNESSolve()`
    2532:   while `SNESComputeFunction()` does. As such, this routine cannot be used with  `MatMFFDSetBase()` with a provided F function value even if it applies the
    2533:   same function as `SNESComputeFunction()` if a `SNESSolve()` right-hand side vector is use because the two functions difference would include this right hand side function.

    2535: .seealso: [](ch_snes), `SNES`, `SNESSetFunction()`, `SNESGetFunction()`, `SNESComputeFunction()`, `MatCreateSNESMF()`, `DMSNESSetMFFunction()`
    2536: @*/
    2537: PetscErrorCode SNESComputeMFFunction(SNES snes, Vec x, Vec y)
    2538: {
    2539:   DM     dm;
    2540:   DMSNES sdm;

    2542:   PetscFunctionBegin;
    2546:   PetscCheckSameComm(snes, 1, x, 2);
    2547:   PetscCheckSameComm(snes, 1, y, 3);
    2548:   PetscCall(VecValidValues_Internal(x, 2, PETSC_TRUE));

    2550:   PetscCall(SNESGetDM(snes, &dm));
    2551:   PetscCall(DMGetDMSNES(dm, &sdm));
    2552:   PetscCall(PetscLogEventBegin(SNES_FunctionEval, snes, x, y, 0));
    2553:   PetscCall(VecLockReadPush(x));
    2554:   /* ensure domainerror is false prior to computefunction evaluation (may not have been reset) */
    2555:   snes->domainerror = PETSC_FALSE;
    2556:   PetscCallBack("SNES callback function", (*sdm->ops->computemffunction)(snes, x, y, sdm->mffunctionctx));
    2557:   PetscCall(VecLockReadPop(x));
    2558:   PetscCall(PetscLogEventEnd(SNES_FunctionEval, snes, x, y, 0));
    2559:   snes->nfuncs++;
    2560:   /*
    2561:      domainerror might not be set on all processes; so we tag vector locally with Inf and the next inner product or norm will
    2562:      propagate the value to all processes
    2563:   */
    2564:   PetscCall(VecFlag(y, snes->domainerror));
    2565:   PetscFunctionReturn(PETSC_SUCCESS);
    2566: }

    2568: /*@
    2569:   SNESComputeNGS - Calls the Gauss-Seidel function that has been set with `SNESSetNGS()`.

    2571:   Collective

    2573:   Input Parameters:
    2574: + snes - the `SNES` context
    2575: . x    - input vector
    2576: - b    - rhs vector

    2578:   Output Parameter:
    2579: . x - new solution vector

    2581:   Level: developer

    2583:   Note:
    2584:   `SNESComputeNGS()` is typically used within composed nonlinear solver
    2585:   implementations, so most users would not generally call this routine
    2586:   themselves.

    2588: .seealso: [](ch_snes), `SNESNGSFn`, `SNESSetNGS()`, `SNESComputeFunction()`, `SNESNGS`
    2589: @*/
    2590: PetscErrorCode SNESComputeNGS(SNES snes, Vec b, Vec x)
    2591: {
    2592:   DM     dm;
    2593:   DMSNES sdm;

    2595:   PetscFunctionBegin;
    2599:   PetscCheckSameComm(snes, 1, x, 3);
    2600:   if (b) PetscCheckSameComm(snes, 1, b, 2);
    2601:   if (b) PetscCall(VecValidValues_Internal(b, 2, PETSC_TRUE));
    2602:   PetscCall(PetscLogEventBegin(SNES_NGSEval, snes, x, b, 0));
    2603:   PetscCall(SNESGetDM(snes, &dm));
    2604:   PetscCall(DMGetDMSNES(dm, &sdm));
    2605:   PetscCheck(sdm->ops->computegs, PETSC_COMM_SELF, PETSC_ERR_ARG_WRONGSTATE, "Must call SNESSetNGS() before SNESComputeNGS(), likely called from SNESSolve().");
    2606:   if (b) PetscCall(VecLockReadPush(b));
    2607:   PetscCallBack("SNES callback NGS", (*sdm->ops->computegs)(snes, x, b, sdm->gsctx));
    2608:   if (b) PetscCall(VecLockReadPop(b));
    2609:   PetscCall(PetscLogEventEnd(SNES_NGSEval, snes, x, b, 0));
    2610:   PetscFunctionReturn(PETSC_SUCCESS);
    2611: }

    2613: static PetscErrorCode SNESComputeFunction_FD(SNES snes, Vec Xin, Vec G)
    2614: {
    2615:   Vec          X;
    2616:   PetscScalar *g;
    2617:   PetscReal    f, f2;
    2618:   PetscInt     low, high, N, i;
    2619:   PetscBool    flg;
    2620:   PetscReal    h = .5 * PETSC_SQRT_MACHINE_EPSILON;

    2622:   PetscFunctionBegin;
    2623:   PetscCall(PetscOptionsGetReal(((PetscObject)snes)->options, ((PetscObject)snes)->prefix, "-snes_fd_delta", &h, &flg));
    2624:   PetscCall(VecDuplicate(Xin, &X));
    2625:   PetscCall(VecCopy(Xin, X));
    2626:   PetscCall(VecGetSize(X, &N));
    2627:   PetscCall(VecGetOwnershipRange(X, &low, &high));
    2628:   PetscCall(VecSetOption(X, VEC_IGNORE_OFF_PROC_ENTRIES, PETSC_TRUE));
    2629:   PetscCall(VecGetArray(G, &g));
    2630:   for (i = 0; i < N; i++) {
    2631:     PetscCall(VecSetValue(X, i, -h, ADD_VALUES));
    2632:     PetscCall(VecAssemblyBegin(X));
    2633:     PetscCall(VecAssemblyEnd(X));
    2634:     PetscCall(SNESComputeObjective(snes, X, &f));
    2635:     PetscCall(VecSetValue(X, i, 2.0 * h, ADD_VALUES));
    2636:     PetscCall(VecAssemblyBegin(X));
    2637:     PetscCall(VecAssemblyEnd(X));
    2638:     PetscCall(SNESComputeObjective(snes, X, &f2));
    2639:     PetscCall(VecSetValue(X, i, -h, ADD_VALUES));
    2640:     PetscCall(VecAssemblyBegin(X));
    2641:     PetscCall(VecAssemblyEnd(X));
    2642:     if (i >= low && i < high) g[i - low] = (f2 - f) / (2.0 * h);
    2643:   }
    2644:   PetscCall(VecRestoreArray(G, &g));
    2645:   PetscCall(VecDestroy(&X));
    2646:   PetscFunctionReturn(PETSC_SUCCESS);
    2647: }

    2649: /*@
    2650:   SNESTestFunction - Computes the difference between the computed and finite-difference functions

    2652:   Collective

    2654:   Input Parameter:
    2655: . snes - the `SNES` context

    2657:   Options Database Keys:
    2658: + -snes_test_function      - compare the user provided function with one compute via finite differences to check for errors.
    2659: - -snes_test_function_view - display the user provided function, the finite difference function and the difference

    2661:   Level: developer

    2663: .seealso: [](ch_snes), `SNESTestJacobian()`, `SNESSetFunction()`, `SNESComputeFunction()`
    2664: @*/
    2665: PetscErrorCode SNESTestFunction(SNES snes)
    2666: {
    2667:   Vec               x, g1, g2, g3;
    2668:   PetscBool         complete_print = PETSC_FALSE;
    2669:   PetscReal         hcnorm, fdnorm, hcmax, fdmax, diffmax, diffnorm;
    2670:   PetscScalar       dot;
    2671:   MPI_Comm          comm;
    2672:   PetscViewer       viewer, mviewer;
    2673:   PetscViewerFormat format;
    2674:   PetscInt          tabs;
    2675:   static PetscBool  directionsprinted = PETSC_FALSE;
    2676:   SNESObjectiveFn  *objective;

    2678:   PetscFunctionBegin;
    2679:   PetscCall(SNESGetObjective(snes, &objective, NULL));
    2680:   if (!objective) PetscFunctionReturn(PETSC_SUCCESS);

    2682:   PetscObjectOptionsBegin((PetscObject)snes);
    2683:   PetscCall(PetscOptionsViewer("-snes_test_function_view", "View difference between hand-coded and finite difference function element entries", "None", &mviewer, &format, &complete_print));
    2684:   PetscOptionsEnd();

    2686:   PetscCall(PetscObjectGetComm((PetscObject)snes, &comm));
    2687:   PetscCall(PetscViewerASCIIGetStdout(comm, &viewer));
    2688:   PetscCall(PetscViewerASCIIGetTab(viewer, &tabs));
    2689:   PetscCall(PetscViewerASCIISetTab(viewer, ((PetscObject)snes)->tablevel));
    2690:   PetscCall(PetscViewerASCIIPrintf(viewer, "  ---------- Testing Function -------------\n"));
    2691:   if (!complete_print && !directionsprinted) {
    2692:     PetscCall(PetscViewerASCIIPrintf(viewer, "  Run with -snes_test_function_view and optionally -snes_test_function <threshold> to show difference\n"));
    2693:     PetscCall(PetscViewerASCIIPrintf(viewer, "    of hand-coded and finite difference function entries greater than <threshold>.\n"));
    2694:   }
    2695:   if (!directionsprinted) {
    2696:     PetscCall(PetscViewerASCIIPrintf(viewer, "  Testing hand-coded Function, if (for double precision runs) ||F - Ffd||/||F|| is\n"));
    2697:     PetscCall(PetscViewerASCIIPrintf(viewer, "    O(1.e-8), the hand-coded Function is probably correct.\n"));
    2698:     directionsprinted = PETSC_TRUE;
    2699:   }
    2700:   if (complete_print) PetscCall(PetscViewerPushFormat(mviewer, format));

    2702:   PetscCall(SNESGetSolution(snes, &x));
    2703:   PetscCall(VecDuplicate(x, &g1));
    2704:   PetscCall(VecDuplicate(x, &g2));
    2705:   PetscCall(VecDuplicate(x, &g3));
    2706:   PetscCall(SNESComputeFunction(snes, x, g1));
    2707:   PetscCall(SNESComputeFunction_FD(snes, x, g2));

    2709:   PetscCall(VecNorm(g2, NORM_2, &fdnorm));
    2710:   PetscCall(VecNorm(g1, NORM_2, &hcnorm));
    2711:   PetscCall(VecNorm(g2, NORM_INFINITY, &fdmax));
    2712:   PetscCall(VecNorm(g1, NORM_INFINITY, &hcmax));
    2713:   PetscCall(VecDot(g1, g2, &dot));
    2714:   PetscCall(VecCopy(g1, g3));
    2715:   PetscCall(VecAXPY(g3, -1.0, g2));
    2716:   PetscCall(VecNorm(g3, NORM_2, &diffnorm));
    2717:   PetscCall(VecNorm(g3, NORM_INFINITY, &diffmax));
    2718:   PetscCall(PetscViewerASCIIPrintf(viewer, "  ||Ffd|| %g, ||F|| = %g, angle cosine = (Ffd'F)/||Ffd||||F|| = %g\n", (double)fdnorm, (double)hcnorm, (double)(PetscRealPart(dot) / (fdnorm * hcnorm))));
    2719:   PetscCall(PetscViewerASCIIPrintf(viewer, "  2-norm ||F - Ffd||/||F|| = %g, ||F - Ffd|| = %g\n", (double)(diffnorm / PetscMax(hcnorm, fdnorm)), (double)diffnorm));
    2720:   PetscCall(PetscViewerASCIIPrintf(viewer, "  max-norm ||F - Ffd||/||F|| = %g, ||F - Ffd|| = %g\n", (double)(diffmax / PetscMax(hcmax, fdmax)), (double)diffmax));

    2722:   if (complete_print) {
    2723:     PetscCall(PetscViewerASCIIPrintf(viewer, "  Hand-coded function ----------\n"));
    2724:     PetscCall(VecView(g1, mviewer));
    2725:     PetscCall(PetscViewerASCIIPrintf(viewer, "  Finite difference function ----------\n"));
    2726:     PetscCall(VecView(g2, mviewer));
    2727:     PetscCall(PetscViewerASCIIPrintf(viewer, "  Hand-coded minus finite-difference function ----------\n"));
    2728:     PetscCall(VecView(g3, mviewer));
    2729:   }
    2730:   PetscCall(VecDestroy(&g1));
    2731:   PetscCall(VecDestroy(&g2));
    2732:   PetscCall(VecDestroy(&g3));

    2734:   if (complete_print) {
    2735:     PetscCall(PetscViewerPopFormat(mviewer));
    2736:     PetscCall(PetscViewerDestroy(&mviewer));
    2737:   }
    2738:   PetscCall(PetscViewerASCIISetTab(viewer, tabs));
    2739:   PetscFunctionReturn(PETSC_SUCCESS);
    2740: }

    2742: /*@
    2743:   SNESTestJacobian - Computes the difference between the computed and finite-difference Jacobians

    2745:   Collective

    2747:   Input Parameter:
    2748: . snes - the `SNES` context

    2750:   Output Parameters:
    2751: + Jnorm    - the Frobenius norm of the computed Jacobian, or `NULL`
    2752: - diffNorm - the Frobenius norm of the difference of the computed and finite-difference Jacobians, or `NULL`

    2754:   Options Database Keys:
    2755: + -snes_test_jacobian <optional threshold> - compare the user provided Jacobian with one compute via finite differences to check for errors.  If a threshold is given, display only those entries whose difference is greater than the threshold.
    2756: - -snes_test_jacobian_view                 - display the user provided Jacobian, the finite difference Jacobian and the difference

    2758:   Level: developer

    2760:   Note:
    2761:   Directions and norms are printed to stdout if `diffNorm` is `NULL`.

    2763: .seealso: [](ch_snes), `SNESTestFunction()`, `SNESSetJacobian()`, `SNESComputeJacobian()`
    2764: @*/
    2765: PetscErrorCode SNESTestJacobian(SNES snes, PetscReal *Jnorm, PetscReal *diffNorm)
    2766: {
    2767:   Mat               A, B, C, D, jacobian;
    2768:   Vec               x = snes->vec_sol, f;
    2769:   PetscReal         nrm, gnorm;
    2770:   PetscReal         threshold = 1.e-5;
    2771:   MatType           mattype;
    2772:   PetscInt          m, n, M, N;
    2773:   void             *functx;
    2774:   PetscBool         complete_print = PETSC_FALSE, threshold_print = PETSC_FALSE, flg, istranspose;
    2775:   PetscBool         silent = diffNorm != PETSC_NULLPTR ? PETSC_TRUE : PETSC_FALSE;
    2776:   PetscViewer       viewer, mviewer;
    2777:   MPI_Comm          comm;
    2778:   PetscInt          tabs;
    2779:   static PetscBool  directionsprinted = PETSC_FALSE;
    2780:   PetscViewerFormat format;

    2782:   PetscFunctionBegin;
    2783:   PetscObjectOptionsBegin((PetscObject)snes);
    2784:   PetscCall(PetscOptionsReal("-snes_test_jacobian", "Threshold for element difference between hand-coded and finite difference being meaningful", "None", threshold, &threshold, NULL));
    2785:   PetscCall(PetscOptionsDeprecated("-snes_test_jacobian_display", "-snes_test_jacobian_view", "3.13", NULL));
    2786:   PetscCall(PetscOptionsViewer("-snes_test_jacobian_view", "View difference between hand-coded and finite difference Jacobians element entries", "None", &mviewer, &format, &complete_print));
    2787:   PetscCall(PetscOptionsDeprecated("-snes_test_jacobian_display_threshold", "-snes_test_jacobian", "3.13", "-snes_test_jacobian accepts an optional threshold (since v3.10)"));
    2788:   PetscCall(PetscOptionsReal("-snes_test_jacobian_display_threshold", "Display difference between hand-coded and finite difference Jacobians which exceed input threshold", "None", threshold, &threshold, &threshold_print));
    2789:   PetscOptionsEnd();

    2791:   PetscCall(PetscObjectGetComm((PetscObject)snes, &comm));
    2792:   PetscCall(PetscViewerASCIIGetStdout(comm, &viewer));
    2793:   PetscCall(PetscViewerASCIIGetTab(viewer, &tabs));
    2794:   PetscCall(PetscViewerASCIISetTab(viewer, ((PetscObject)snes)->tablevel));
    2795:   if (!silent) PetscCall(PetscViewerASCIIPrintf(viewer, "  ---------- Testing Jacobian -------------\n"));
    2796:   if (!complete_print && !silent && !directionsprinted) {
    2797:     PetscCall(PetscViewerASCIIPrintf(viewer, "  Run with -snes_test_jacobian_view and optionally -snes_test_jacobian <threshold> to show difference\n"));
    2798:     PetscCall(PetscViewerASCIIPrintf(viewer, "    of hand-coded and finite difference Jacobian entries greater than <threshold>.\n"));
    2799:   }
    2800:   if (!directionsprinted && !silent) {
    2801:     PetscCall(PetscViewerASCIIPrintf(viewer, "  Testing hand-coded Jacobian, if (for double precision runs) ||J - Jfd||_F/||J||_F is\n"));
    2802:     PetscCall(PetscViewerASCIIPrintf(viewer, "    O(1.e-8), the hand-coded Jacobian is probably correct.\n"));
    2803:     directionsprinted = PETSC_TRUE;
    2804:   }
    2805:   if (complete_print) PetscCall(PetscViewerPushFormat(mviewer, format));

    2807:   PetscCall(PetscObjectTypeCompare((PetscObject)snes->jacobian, MATMFFD, &flg));
    2808:   if (!flg) jacobian = snes->jacobian;
    2809:   else jacobian = snes->jacobian_pre;

    2811:   if (!x) PetscCall(MatCreateVecs(jacobian, &x, NULL));
    2812:   else PetscCall(PetscObjectReference((PetscObject)x));
    2813:   PetscCall(VecDuplicate(x, &f));

    2815:   /* evaluate the function at this point because SNESComputeJacobianDefault() assumes that the function has been evaluated and put into snes->vec_func */
    2816:   PetscCall(SNESComputeFunction(snes, x, f));
    2817:   PetscCall(VecDestroy(&f));
    2818:   PetscCall(PetscObjectTypeCompare((PetscObject)snes, SNESKSPTRANSPOSEONLY, &istranspose));
    2819:   while (jacobian) {
    2820:     Mat JT = NULL, Jsave = NULL;

    2822:     if (istranspose) {
    2823:       PetscCall(MatCreateTranspose(jacobian, &JT));
    2824:       Jsave    = jacobian;
    2825:       jacobian = JT;
    2826:     }
    2827:     PetscCall(PetscObjectBaseTypeCompareAny((PetscObject)jacobian, &flg, MATSEQAIJ, MATMPIAIJ, MATSEQDENSE, MATMPIDENSE, MATSEQBAIJ, MATMPIBAIJ, MATSEQSBAIJ, MATMPISBAIJ, ""));
    2828:     if (flg) {
    2829:       A = jacobian;
    2830:       PetscCall(PetscObjectReference((PetscObject)A));
    2831:     } else {
    2832:       PetscCall(MatComputeOperator(jacobian, MATAIJ, &A));
    2833:     }

    2835:     PetscCall(MatGetType(A, &mattype));
    2836:     PetscCall(MatGetSize(A, &M, &N));
    2837:     PetscCall(MatGetLocalSize(A, &m, &n));
    2838:     PetscCall(MatCreate(PetscObjectComm((PetscObject)A), &B));
    2839:     PetscCall(MatSetType(B, mattype));
    2840:     PetscCall(MatSetSizes(B, m, n, M, N));
    2841:     PetscCall(MatSetBlockSizesFromMats(B, A, A));
    2842:     PetscCall(MatSetUp(B));
    2843:     PetscCall(MatSetOption(B, MAT_NEW_NONZERO_ALLOCATION_ERR, PETSC_FALSE));

    2845:     PetscCall(SNESGetFunction(snes, NULL, NULL, &functx));
    2846:     PetscCall(SNESComputeJacobianDefault(snes, x, B, B, functx));

    2848:     PetscCall(MatDuplicate(B, MAT_COPY_VALUES, &D));
    2849:     PetscCall(MatAYPX(D, -1.0, A, DIFFERENT_NONZERO_PATTERN));
    2850:     PetscCall(MatNorm(D, NORM_FROBENIUS, &nrm));
    2851:     PetscCall(MatNorm(A, NORM_FROBENIUS, &gnorm));
    2852:     PetscCall(MatDestroy(&D));
    2853:     if (!gnorm) gnorm = 1; /* just in case */
    2854:     if (!silent) PetscCall(PetscViewerASCIIPrintf(viewer, "  ||J - Jfd||_F/||J||_F = %g, ||J - Jfd||_F = %g\n", (double)(nrm / gnorm), (double)nrm));
    2855:     if (complete_print) {
    2856:       PetscCall(PetscViewerASCIIPrintf(viewer, "  Hand-coded Jacobian ----------\n"));
    2857:       PetscCall(MatView(A, mviewer));
    2858:       PetscCall(PetscViewerASCIIPrintf(viewer, "  Finite difference Jacobian ----------\n"));
    2859:       PetscCall(MatView(B, mviewer));
    2860:     }

    2862:     if (threshold_print || complete_print) {
    2863:       PetscInt           Istart, Iend, *ccols, bncols, cncols, j, row;
    2864:       PetscScalar       *cvals;
    2865:       const PetscInt    *bcols;
    2866:       const PetscScalar *bvals;

    2868:       PetscCall(MatCreate(PetscObjectComm((PetscObject)A), &C));
    2869:       PetscCall(MatSetType(C, mattype));
    2870:       PetscCall(MatSetSizes(C, m, n, M, N));
    2871:       PetscCall(MatSetBlockSizesFromMats(C, A, A));
    2872:       PetscCall(MatSetUp(C));
    2873:       PetscCall(MatSetOption(C, MAT_NEW_NONZERO_ALLOCATION_ERR, PETSC_FALSE));

    2875:       PetscCall(MatAYPX(B, -1.0, A, DIFFERENT_NONZERO_PATTERN));
    2876:       PetscCall(MatGetOwnershipRange(B, &Istart, &Iend));

    2878:       for (row = Istart; row < Iend; row++) {
    2879:         PetscCall(MatGetRow(B, row, &bncols, &bcols, &bvals));
    2880:         PetscCall(PetscMalloc2(bncols, &ccols, bncols, &cvals));
    2881:         for (j = 0, cncols = 0; j < bncols; j++) {
    2882:           if (PetscAbsScalar(bvals[j]) > threshold) {
    2883:             ccols[cncols] = bcols[j];
    2884:             cvals[cncols] = bvals[j];
    2885:             cncols += 1;
    2886:           }
    2887:         }
    2888:         if (cncols) PetscCall(MatSetValues(C, 1, &row, cncols, ccols, cvals, INSERT_VALUES));
    2889:         PetscCall(MatRestoreRow(B, row, &bncols, &bcols, &bvals));
    2890:         PetscCall(PetscFree2(ccols, cvals));
    2891:       }
    2892:       PetscCall(MatAssemblyBegin(C, MAT_FINAL_ASSEMBLY));
    2893:       PetscCall(MatAssemblyEnd(C, MAT_FINAL_ASSEMBLY));
    2894:       PetscCall(PetscViewerASCIIPrintf(viewer, "  Hand-coded minus finite-difference Jacobian with tolerance %g ----------\n", (double)threshold));
    2895:       PetscCall(MatView(C, complete_print ? mviewer : viewer));
    2896:       PetscCall(MatDestroy(&C));
    2897:     }
    2898:     PetscCall(MatDestroy(&A));
    2899:     PetscCall(MatDestroy(&B));
    2900:     PetscCall(MatDestroy(&JT));
    2901:     if (Jsave) jacobian = Jsave;
    2902:     if (jacobian != snes->jacobian_pre) {
    2903:       jacobian = snes->jacobian_pre;
    2904:       if (!silent) PetscCall(PetscViewerASCIIPrintf(viewer, "  ---------- Testing Jacobian for preconditioner -------------\n"));
    2905:     } else jacobian = NULL;
    2906:   }
    2907:   PetscCall(VecDestroy(&x));
    2908:   if (complete_print) PetscCall(PetscViewerPopFormat(mviewer));
    2909:   if (mviewer) PetscCall(PetscViewerDestroy(&mviewer));
    2910:   PetscCall(PetscViewerASCIISetTab(viewer, tabs));

    2912:   if (Jnorm) *Jnorm = gnorm;
    2913:   if (diffNorm) *diffNorm = nrm;
    2914:   PetscFunctionReturn(PETSC_SUCCESS);
    2915: }

    2917: /*@
    2918:   SNESComputeJacobian - Computes the Jacobian matrix that has been set with `SNESSetJacobian()`.

    2920:   Collective

    2922:   Input Parameters:
    2923: + snes - the `SNES` context
    2924: - X    - input vector

    2926:   Output Parameters:
    2927: + A - Jacobian matrix
    2928: - B - optional matrix for building the preconditioner, usually the same as `A`

    2930:   Options Database Keys:
    2931: + -snes_lag_preconditioner <lag>           - how often to rebuild preconditioner
    2932: . -snes_lag_jacobian <lag>                 - how often to rebuild Jacobian
    2933: . -snes_test_jacobian <optional threshold> - compare the user provided Jacobian with one compute via finite differences to check for errors.  If a threshold is given, display only those entries whose difference is greater than the threshold.
    2934: . -snes_test_jacobian_view                 - display the user provided Jacobian, the finite difference Jacobian and the difference between them to help users detect the location of errors in the user provided Jacobian
    2935: . -snes_compare_explicit                   - Compare the computed Jacobian to the finite difference Jacobian and output the differences
    2936: . -snes_compare_explicit_draw              - Compare the computed Jacobian to the finite difference Jacobian and draw the result
    2937: . -snes_compare_explicit_contour           - Compare the computed Jacobian to the finite difference Jacobian and draw a contour plot with the result
    2938: . -snes_compare_operator                   - Make the comparison options above use the operator instead of the matrix used to construct the preconditioner
    2939: . -snes_compare_coloring                   - Compute the finite difference Jacobian using coloring and display norms of difference
    2940: . -snes_compare_coloring_display           - Compute the finite difference Jacobian using coloring and display verbose differences
    2941: . -snes_compare_coloring_threshold         - Display only those matrix entries that differ by more than a given threshold
    2942: . -snes_compare_coloring_threshold_atol    - Absolute tolerance for difference in matrix entries to be displayed by `-snes_compare_coloring_threshold`
    2943: . -snes_compare_coloring_threshold_rtol    - Relative tolerance for difference in matrix entries to be displayed by `-snes_compare_coloring_threshold`
    2944: . -snes_compare_coloring_draw              - Compute the finite difference Jacobian using coloring and draw differences
    2945: - -snes_compare_coloring_draw_contour      - Compute the finite difference Jacobian using coloring and show contours of matrices and differences

    2947:   Level: developer

    2949:   Note:
    2950:   Most users should not need to explicitly call this routine, as it
    2951:   is used internally within the nonlinear solvers.

    2953:   Developer Note:
    2954:   This has duplicative ways of checking the accuracy of the user provided Jacobian (see the options above). This is for historical reasons, the routine `SNESTestJacobian()` use to used
    2955:   with the `SNESType` of test that has been removed.

    2957: .seealso: [](ch_snes), `SNESSetJacobian()`, `KSPSetOperators()`, `MatStructure`, `SNESSetLagPreconditioner()`, `SNESSetLagJacobian()`
    2958: @*/
    2959: PetscErrorCode SNESComputeJacobian(SNES snes, Vec X, Mat A, Mat B)
    2960: {
    2961:   PetscBool flag;
    2962:   DM        dm;
    2963:   DMSNES    sdm;
    2964:   KSP       ksp;

    2966:   PetscFunctionBegin;
    2969:   PetscCheckSameComm(snes, 1, X, 2);
    2970:   PetscCall(VecValidValues_Internal(X, 2, PETSC_TRUE));
    2971:   PetscCall(SNESGetDM(snes, &dm));
    2972:   PetscCall(DMGetDMSNES(dm, &sdm));

    2974:   /* make sure that MatAssemblyBegin/End() is called on A matrix if it is matrix-free */
    2975:   if (snes->lagjacobian == -2) {
    2976:     snes->lagjacobian = -1;

    2978:     PetscCall(PetscInfo(snes, "Recomputing Jacobian/preconditioner because lag is -2 (means compute Jacobian, but then never again) \n"));
    2979:   } else if (snes->lagjacobian == -1) {
    2980:     PetscCall(PetscInfo(snes, "Reusing Jacobian/preconditioner because lag is -1\n"));
    2981:     PetscCall(PetscObjectTypeCompare((PetscObject)A, MATMFFD, &flag));
    2982:     if (flag) {
    2983:       PetscCall(MatAssemblyBegin(A, MAT_FINAL_ASSEMBLY));
    2984:       PetscCall(MatAssemblyEnd(A, MAT_FINAL_ASSEMBLY));
    2985:     }
    2986:     PetscFunctionReturn(PETSC_SUCCESS);
    2987:   } else if (snes->lagjacobian > 1 && (snes->iter + snes->jac_iter) % snes->lagjacobian) {
    2988:     PetscCall(PetscInfo(snes, "Reusing Jacobian/preconditioner because lag is %" PetscInt_FMT " and SNES iteration is %" PetscInt_FMT "\n", snes->lagjacobian, snes->iter));
    2989:     PetscCall(PetscObjectTypeCompare((PetscObject)A, MATMFFD, &flag));
    2990:     if (flag) {
    2991:       PetscCall(MatAssemblyBegin(A, MAT_FINAL_ASSEMBLY));
    2992:       PetscCall(MatAssemblyEnd(A, MAT_FINAL_ASSEMBLY));
    2993:     }
    2994:     PetscFunctionReturn(PETSC_SUCCESS);
    2995:   }
    2996:   if (snes->npc && snes->npcside == PC_LEFT) {
    2997:     PetscCall(MatAssemblyBegin(A, MAT_FINAL_ASSEMBLY));
    2998:     PetscCall(MatAssemblyEnd(A, MAT_FINAL_ASSEMBLY));
    2999:     PetscFunctionReturn(PETSC_SUCCESS);
    3000:   }

    3002:   PetscCall(PetscLogEventBegin(SNES_JacobianEval, snes, X, A, B));
    3003:   PetscCall(VecLockReadPush(X));
    3004:   {
    3005:     void           *ctx;
    3006:     SNESJacobianFn *J;
    3007:     PetscCall(DMSNESGetJacobian(dm, &J, &ctx));
    3008:     PetscCallBack("SNES callback Jacobian", (*J)(snes, X, A, B, ctx));
    3009:   }
    3010:   PetscCall(VecLockReadPop(X));
    3011:   PetscCall(PetscLogEventEnd(SNES_JacobianEval, snes, X, A, B));

    3013:   /* attach latest linearization point to the matrix used to construct the preconditioner */
    3014:   PetscCall(PetscObjectCompose((PetscObject)B, "__SNES_latest_X", (PetscObject)X));

    3016:   /* the next line ensures that snes->ksp exists */
    3017:   PetscCall(SNESGetKSP(snes, &ksp));
    3018:   if (snes->lagpreconditioner == -2) {
    3019:     PetscCall(PetscInfo(snes, "Rebuilding preconditioner exactly once since lag is -2\n"));
    3020:     PetscCall(KSPSetReusePreconditioner(snes->ksp, PETSC_FALSE));
    3021:     snes->lagpreconditioner = -1;
    3022:   } else if (snes->lagpreconditioner == -1) {
    3023:     PetscCall(PetscInfo(snes, "Reusing preconditioner because lag is -1\n"));
    3024:     PetscCall(KSPSetReusePreconditioner(snes->ksp, PETSC_TRUE));
    3025:   } else if (snes->lagpreconditioner > 1 && (snes->iter + snes->pre_iter) % snes->lagpreconditioner) {
    3026:     PetscCall(PetscInfo(snes, "Reusing preconditioner because lag is %" PetscInt_FMT " and SNES iteration is %" PetscInt_FMT "\n", snes->lagpreconditioner, snes->iter));
    3027:     PetscCall(KSPSetReusePreconditioner(snes->ksp, PETSC_TRUE));
    3028:   } else {
    3029:     PetscCall(PetscInfo(snes, "Rebuilding preconditioner\n"));
    3030:     PetscCall(KSPSetReusePreconditioner(snes->ksp, PETSC_FALSE));
    3031:   }

    3033:   /* monkey business to allow testing Jacobians in multilevel solvers.
    3034:      This is needed because the SNESTestXXX interface does not accept vectors and matrices */
    3035:   {
    3036:     Vec xsave            = snes->vec_sol;
    3037:     Mat jacobiansave     = snes->jacobian;
    3038:     Mat jacobian_presave = snes->jacobian_pre;

    3040:     snes->vec_sol      = X;
    3041:     snes->jacobian     = A;
    3042:     snes->jacobian_pre = B;
    3043:     if (snes->testFunc) PetscCall(SNESTestFunction(snes));
    3044:     if (snes->testJac) PetscCall(SNESTestJacobian(snes, NULL, NULL));

    3046:     snes->vec_sol      = xsave;
    3047:     snes->jacobian     = jacobiansave;
    3048:     snes->jacobian_pre = jacobian_presave;
    3049:   }

    3051:   {
    3052:     PetscBool flag = PETSC_FALSE, flag_draw = PETSC_FALSE, flag_contour = PETSC_FALSE, flag_operator = PETSC_FALSE;
    3053:     PetscCall(PetscOptionsCreateViewer(PetscObjectComm((PetscObject)snes), ((PetscObject)snes)->options, ((PetscObject)snes)->prefix, "-snes_compare_explicit", NULL, NULL, &flag));
    3054:     PetscCall(PetscOptionsCreateViewer(PetscObjectComm((PetscObject)snes), ((PetscObject)snes)->options, ((PetscObject)snes)->prefix, "-snes_compare_explicit_draw", NULL, NULL, &flag_draw));
    3055:     PetscCall(PetscOptionsCreateViewer(PetscObjectComm((PetscObject)snes), ((PetscObject)snes)->options, ((PetscObject)snes)->prefix, "-snes_compare_explicit_draw_contour", NULL, NULL, &flag_contour));
    3056:     PetscCall(PetscOptionsCreateViewer(PetscObjectComm((PetscObject)snes), ((PetscObject)snes)->options, ((PetscObject)snes)->prefix, "-snes_compare_operator", NULL, NULL, &flag_operator));
    3057:     if (flag || flag_draw || flag_contour) {
    3058:       Mat         Bexp_mine = NULL, Bexp, FDexp;
    3059:       PetscViewer vdraw, vstdout;
    3060:       PetscBool   flg;
    3061:       if (flag_operator) {
    3062:         PetscCall(MatComputeOperator(A, MATAIJ, &Bexp_mine));
    3063:         Bexp = Bexp_mine;
    3064:       } else {
    3065:         /* See if the matrix used to construct the preconditioner can be viewed and added directly */
    3066:         PetscCall(PetscObjectBaseTypeCompareAny((PetscObject)B, &flg, MATSEQAIJ, MATMPIAIJ, MATSEQDENSE, MATMPIDENSE, MATSEQBAIJ, MATMPIBAIJ, MATSEQSBAIJ, MATMPISBAIJ, ""));
    3067:         if (flg) Bexp = B;
    3068:         else {
    3069:           /* If the "preconditioning" matrix is itself MATSHELL or some other type without direct support */
    3070:           PetscCall(MatComputeOperator(B, MATAIJ, &Bexp_mine));
    3071:           Bexp = Bexp_mine;
    3072:         }
    3073:       }
    3074:       PetscCall(MatConvert(Bexp, MATSAME, MAT_INITIAL_MATRIX, &FDexp));
    3075:       PetscCall(SNESComputeJacobianDefault(snes, X, FDexp, FDexp, NULL));
    3076:       PetscCall(PetscViewerASCIIGetStdout(PetscObjectComm((PetscObject)snes), &vstdout));
    3077:       if (flag_draw || flag_contour) {
    3078:         PetscCall(PetscViewerDrawOpen(PetscObjectComm((PetscObject)snes), NULL, "Explicit Jacobians", PETSC_DECIDE, PETSC_DECIDE, 300, 300, &vdraw));
    3079:         if (flag_contour) PetscCall(PetscViewerPushFormat(vdraw, PETSC_VIEWER_DRAW_CONTOUR));
    3080:       } else vdraw = NULL;
    3081:       PetscCall(PetscViewerASCIIPrintf(vstdout, "Explicit %s\n", flag_operator ? "Jacobian" : "preconditioning Jacobian"));
    3082:       if (flag) PetscCall(MatView(Bexp, vstdout));
    3083:       if (vdraw) PetscCall(MatView(Bexp, vdraw));
    3084:       PetscCall(PetscViewerASCIIPrintf(vstdout, "Finite difference Jacobian\n"));
    3085:       if (flag) PetscCall(MatView(FDexp, vstdout));
    3086:       if (vdraw) PetscCall(MatView(FDexp, vdraw));
    3087:       PetscCall(MatAYPX(FDexp, -1.0, Bexp, SAME_NONZERO_PATTERN));
    3088:       PetscCall(PetscViewerASCIIPrintf(vstdout, "User-provided matrix minus finite difference Jacobian\n"));
    3089:       if (flag) PetscCall(MatView(FDexp, vstdout));
    3090:       if (vdraw) { /* Always use contour for the difference */
    3091:         PetscCall(PetscViewerPushFormat(vdraw, PETSC_VIEWER_DRAW_CONTOUR));
    3092:         PetscCall(MatView(FDexp, vdraw));
    3093:         PetscCall(PetscViewerPopFormat(vdraw));
    3094:       }
    3095:       if (flag_contour) PetscCall(PetscViewerPopFormat(vdraw));
    3096:       PetscCall(PetscViewerDestroy(&vdraw));
    3097:       PetscCall(MatDestroy(&Bexp_mine));
    3098:       PetscCall(MatDestroy(&FDexp));
    3099:     }
    3100:   }
    3101:   {
    3102:     PetscBool flag = PETSC_FALSE, flag_display = PETSC_FALSE, flag_draw = PETSC_FALSE, flag_contour = PETSC_FALSE, flag_threshold = PETSC_FALSE;
    3103:     PetscReal threshold_atol = PETSC_SQRT_MACHINE_EPSILON, threshold_rtol = 10 * PETSC_SQRT_MACHINE_EPSILON;
    3104:     PetscCall(PetscOptionsCreateViewer(PetscObjectComm((PetscObject)snes), ((PetscObject)snes)->options, ((PetscObject)snes)->prefix, "-snes_compare_coloring", NULL, NULL, &flag));
    3105:     PetscCall(PetscOptionsCreateViewer(PetscObjectComm((PetscObject)snes), ((PetscObject)snes)->options, ((PetscObject)snes)->prefix, "-snes_compare_coloring_display", NULL, NULL, &flag_display));
    3106:     PetscCall(PetscOptionsCreateViewer(PetscObjectComm((PetscObject)snes), ((PetscObject)snes)->options, ((PetscObject)snes)->prefix, "-snes_compare_coloring_draw", NULL, NULL, &flag_draw));
    3107:     PetscCall(PetscOptionsCreateViewer(PetscObjectComm((PetscObject)snes), ((PetscObject)snes)->options, ((PetscObject)snes)->prefix, "-snes_compare_coloring_draw_contour", NULL, NULL, &flag_contour));
    3108:     PetscCall(PetscOptionsCreateViewer(PetscObjectComm((PetscObject)snes), ((PetscObject)snes)->options, ((PetscObject)snes)->prefix, "-snes_compare_coloring_threshold", NULL, NULL, &flag_threshold));
    3109:     if (flag_threshold) {
    3110:       PetscCall(PetscOptionsGetReal(((PetscObject)snes)->options, ((PetscObject)snes)->prefix, "-snes_compare_coloring_threshold_rtol", &threshold_rtol, NULL));
    3111:       PetscCall(PetscOptionsGetReal(((PetscObject)snes)->options, ((PetscObject)snes)->prefix, "-snes_compare_coloring_threshold_atol", &threshold_atol, NULL));
    3112:     }
    3113:     if (flag || flag_display || flag_draw || flag_contour || flag_threshold) {
    3114:       Mat             Bfd;
    3115:       PetscViewer     vdraw, vstdout;
    3116:       MatColoring     coloring;
    3117:       ISColoring      iscoloring;
    3118:       MatFDColoring   matfdcoloring;
    3119:       SNESFunctionFn *func;
    3120:       void           *funcctx;
    3121:       PetscReal       norm1, norm2, normmax;

    3123:       PetscCall(MatDuplicate(B, MAT_DO_NOT_COPY_VALUES, &Bfd));
    3124:       PetscCall(MatColoringCreate(Bfd, &coloring));
    3125:       PetscCall(MatColoringSetType(coloring, MATCOLORINGSL));
    3126:       PetscCall(MatColoringSetFromOptions(coloring));
    3127:       PetscCall(MatColoringApply(coloring, &iscoloring));
    3128:       PetscCall(MatColoringDestroy(&coloring));
    3129:       PetscCall(MatFDColoringCreate(Bfd, iscoloring, &matfdcoloring));
    3130:       PetscCall(MatFDColoringSetFromOptions(matfdcoloring));
    3131:       PetscCall(MatFDColoringSetUp(Bfd, iscoloring, matfdcoloring));
    3132:       PetscCall(ISColoringDestroy(&iscoloring));

    3134:       /* This method of getting the function is currently unreliable since it doesn't work for DM local functions. */
    3135:       PetscCall(SNESGetFunction(snes, NULL, &func, &funcctx));
    3136:       PetscCall(MatFDColoringSetFunction(matfdcoloring, (MatFDColoringFn *)func, funcctx));
    3137:       PetscCall(PetscObjectSetOptionsPrefix((PetscObject)matfdcoloring, ((PetscObject)snes)->prefix));
    3138:       PetscCall(PetscObjectAppendOptionsPrefix((PetscObject)matfdcoloring, "coloring_"));
    3139:       PetscCall(MatFDColoringSetFromOptions(matfdcoloring));
    3140:       PetscCall(MatFDColoringApply(Bfd, matfdcoloring, X, snes));
    3141:       PetscCall(MatFDColoringDestroy(&matfdcoloring));

    3143:       PetscCall(PetscViewerASCIIGetStdout(PetscObjectComm((PetscObject)snes), &vstdout));
    3144:       if (flag_draw || flag_contour) {
    3145:         PetscCall(PetscViewerDrawOpen(PetscObjectComm((PetscObject)snes), NULL, "Colored Jacobians", PETSC_DECIDE, PETSC_DECIDE, 300, 300, &vdraw));
    3146:         if (flag_contour) PetscCall(PetscViewerPushFormat(vdraw, PETSC_VIEWER_DRAW_CONTOUR));
    3147:       } else vdraw = NULL;
    3148:       PetscCall(PetscViewerASCIIPrintf(vstdout, "Explicit preconditioning Jacobian\n"));
    3149:       if (flag_display) PetscCall(MatView(B, vstdout));
    3150:       if (vdraw) PetscCall(MatView(B, vdraw));
    3151:       PetscCall(PetscViewerASCIIPrintf(vstdout, "Colored Finite difference Jacobian\n"));
    3152:       if (flag_display) PetscCall(MatView(Bfd, vstdout));
    3153:       if (vdraw) PetscCall(MatView(Bfd, vdraw));
    3154:       PetscCall(MatAYPX(Bfd, -1.0, B, SAME_NONZERO_PATTERN));
    3155:       PetscCall(MatNorm(Bfd, NORM_1, &norm1));
    3156:       PetscCall(MatNorm(Bfd, NORM_FROBENIUS, &norm2));
    3157:       PetscCall(MatNorm(Bfd, NORM_MAX, &normmax));
    3158:       PetscCall(PetscViewerASCIIPrintf(vstdout, "User-provided matrix minus finite difference Jacobian, norm1=%g normFrob=%g normmax=%g\n", (double)norm1, (double)norm2, (double)normmax));
    3159:       if (flag_display) PetscCall(MatView(Bfd, vstdout));
    3160:       if (vdraw) { /* Always use contour for the difference */
    3161:         PetscCall(PetscViewerPushFormat(vdraw, PETSC_VIEWER_DRAW_CONTOUR));
    3162:         PetscCall(MatView(Bfd, vdraw));
    3163:         PetscCall(PetscViewerPopFormat(vdraw));
    3164:       }
    3165:       if (flag_contour) PetscCall(PetscViewerPopFormat(vdraw));

    3167:       if (flag_threshold) {
    3168:         PetscInt bs, rstart, rend, i;
    3169:         PetscCall(MatGetBlockSize(B, &bs));
    3170:         PetscCall(MatGetOwnershipRange(B, &rstart, &rend));
    3171:         for (i = rstart; i < rend; i++) {
    3172:           const PetscScalar *ba, *ca;
    3173:           const PetscInt    *bj, *cj;
    3174:           PetscInt           bn, cn, j, maxentrycol = -1, maxdiffcol = -1, maxrdiffcol = -1;
    3175:           PetscReal          maxentry = 0, maxdiff = 0, maxrdiff = 0;
    3176:           PetscCall(MatGetRow(B, i, &bn, &bj, &ba));
    3177:           PetscCall(MatGetRow(Bfd, i, &cn, &cj, &ca));
    3178:           PetscCheck(bn == cn, ((PetscObject)A)->comm, PETSC_ERR_PLIB, "Unexpected different nonzero pattern in -snes_compare_coloring_threshold");
    3179:           for (j = 0; j < bn; j++) {
    3180:             PetscReal rdiff = PetscAbsScalar(ca[j]) / (threshold_atol + threshold_rtol * PetscAbsScalar(ba[j]));
    3181:             if (PetscAbsScalar(ba[j]) > PetscAbs(maxentry)) {
    3182:               maxentrycol = bj[j];
    3183:               maxentry    = PetscRealPart(ba[j]);
    3184:             }
    3185:             if (PetscAbsScalar(ca[j]) > PetscAbs(maxdiff)) {
    3186:               maxdiffcol = bj[j];
    3187:               maxdiff    = PetscRealPart(ca[j]);
    3188:             }
    3189:             if (rdiff > maxrdiff) {
    3190:               maxrdiffcol = bj[j];
    3191:               maxrdiff    = rdiff;
    3192:             }
    3193:           }
    3194:           if (maxrdiff > 1) {
    3195:             PetscCall(PetscViewerASCIIPrintf(vstdout, "row %" PetscInt_FMT " (maxentry=%g at %" PetscInt_FMT ", maxdiff=%g at %" PetscInt_FMT ", maxrdiff=%g at %" PetscInt_FMT "):", i, (double)maxentry, maxentrycol, (double)maxdiff, maxdiffcol, (double)maxrdiff, maxrdiffcol));
    3196:             for (j = 0; j < bn; j++) {
    3197:               PetscReal rdiff;
    3198:               rdiff = PetscAbsScalar(ca[j]) / (threshold_atol + threshold_rtol * PetscAbsScalar(ba[j]));
    3199:               if (rdiff > 1) PetscCall(PetscViewerASCIIPrintf(vstdout, " (%" PetscInt_FMT ",%g:%g)", bj[j], (double)PetscRealPart(ba[j]), (double)PetscRealPart(ca[j])));
    3200:             }
    3201:             PetscCall(PetscViewerASCIIPrintf(vstdout, "\n"));
    3202:           }
    3203:           PetscCall(MatRestoreRow(B, i, &bn, &bj, &ba));
    3204:           PetscCall(MatRestoreRow(Bfd, i, &cn, &cj, &ca));
    3205:         }
    3206:       }
    3207:       PetscCall(PetscViewerDestroy(&vdraw));
    3208:       PetscCall(MatDestroy(&Bfd));
    3209:     }
    3210:   }
    3211:   PetscFunctionReturn(PETSC_SUCCESS);
    3212: }

    3214: /*@C
    3215:   SNESSetJacobian - Sets the function to compute Jacobian as well as the
    3216:   location to store the matrix.

    3218:   Logically Collective

    3220:   Input Parameters:
    3221: + snes - the `SNES` context
    3222: . Amat - the matrix that defines the (approximate) Jacobian
    3223: . Pmat - the matrix to be used in constructing the preconditioner, usually the same as `Amat`.
    3224: . J    - Jacobian evaluation routine (if `NULL` then `SNES` retains any previously set value), see `SNESJacobianFn` for details
    3225: - ctx  - [optional] user-defined context for private data for the
    3226:          Jacobian evaluation routine (may be `NULL`) (if `NULL` then `SNES` retains any previously set value)

    3228:   Level: beginner

    3230:   Notes:
    3231:   If the `Amat` matrix and `Pmat` matrix are different you must call `MatAssemblyBegin()`/`MatAssemblyEnd()` on
    3232:   each matrix.

    3234:   If you know the operator `Amat` has a null space you can use `MatSetNullSpace()` and `MatSetTransposeNullSpace()` to supply the null
    3235:   space to `Amat` and the `KSP` solvers will automatically use that null space as needed during the solution process.

    3237:   If using `SNESComputeJacobianDefaultColor()` to assemble a Jacobian, the `ctx` argument
    3238:   must be a `MatFDColoring`.

    3240:   Other defect-correction schemes can be used by computing a different matrix in place of the Jacobian.  One common
    3241:   example is to use the "Picard linearization" which only differentiates through the highest order parts of each term using `SNESSetPicard()`

    3243: .seealso: [](ch_snes), `SNES`, `KSPSetOperators()`, `SNESSetFunction()`, `MatMFFDComputeJacobian()`, `SNESComputeJacobianDefaultColor()`, `MatStructure`,
    3244:           `SNESSetPicard()`, `SNESJacobianFn`, `SNESFunctionFn`
    3245: @*/
    3246: PetscErrorCode SNESSetJacobian(SNES snes, Mat Amat, Mat Pmat, SNESJacobianFn *J, void *ctx)
    3247: {
    3248:   DM dm;

    3250:   PetscFunctionBegin;
    3254:   if (Amat) PetscCheckSameComm(snes, 1, Amat, 2);
    3255:   if (Pmat) PetscCheckSameComm(snes, 1, Pmat, 3);
    3256:   PetscCall(SNESGetDM(snes, &dm));
    3257:   PetscCall(DMSNESSetJacobian(dm, J, ctx));
    3258:   if (Amat) {
    3259:     PetscCall(PetscObjectReference((PetscObject)Amat));
    3260:     PetscCall(MatDestroy(&snes->jacobian));

    3262:     snes->jacobian = Amat;
    3263:   }
    3264:   if (Pmat) {
    3265:     PetscCall(PetscObjectReference((PetscObject)Pmat));
    3266:     PetscCall(MatDestroy(&snes->jacobian_pre));

    3268:     snes->jacobian_pre = Pmat;
    3269:   }
    3270:   PetscFunctionReturn(PETSC_SUCCESS);
    3271: }

    3273: /*@C
    3274:   SNESGetJacobian - Returns the Jacobian matrix and optionally the user
    3275:   provided context for evaluating the Jacobian.

    3277:   Not Collective, but `Mat` object will be parallel if `SNES` is

    3279:   Input Parameter:
    3280: . snes - the nonlinear solver context

    3282:   Output Parameters:
    3283: + Amat - location to stash (approximate) Jacobian matrix (or `NULL`)
    3284: . Pmat - location to stash matrix used to compute the preconditioner (or `NULL`)
    3285: . J    - location to put Jacobian function (or `NULL`), for calling sequence see `SNESJacobianFn`
    3286: - ctx  - location to stash Jacobian ctx (or `NULL`)

    3288:   Level: advanced

    3290: .seealso: [](ch_snes), `SNES`, `Mat`, `SNESSetJacobian()`, `SNESComputeJacobian()`, `SNESJacobianFn`, `SNESGetFunction()`
    3291: @*/
    3292: PetscErrorCode SNESGetJacobian(SNES snes, Mat *Amat, Mat *Pmat, SNESJacobianFn **J, void **ctx)
    3293: {
    3294:   DM dm;

    3296:   PetscFunctionBegin;
    3298:   if (Amat) *Amat = snes->jacobian;
    3299:   if (Pmat) *Pmat = snes->jacobian_pre;
    3300:   PetscCall(SNESGetDM(snes, &dm));
    3301:   PetscCall(DMSNESGetJacobian(dm, J, ctx));
    3302:   PetscFunctionReturn(PETSC_SUCCESS);
    3303: }

    3305: static PetscErrorCode SNESSetDefaultComputeJacobian(SNES snes)
    3306: {
    3307:   DM     dm;
    3308:   DMSNES sdm;

    3310:   PetscFunctionBegin;
    3311:   PetscCall(SNESGetDM(snes, &dm));
    3312:   PetscCall(DMGetDMSNES(dm, &sdm));
    3313:   if (!sdm->ops->computejacobian && snes->jacobian_pre) {
    3314:     DM        dm;
    3315:     PetscBool isdense, ismf;

    3317:     PetscCall(SNESGetDM(snes, &dm));
    3318:     PetscCall(PetscObjectTypeCompareAny((PetscObject)snes->jacobian_pre, &isdense, MATSEQDENSE, MATMPIDENSE, MATDENSE, NULL));
    3319:     PetscCall(PetscObjectTypeCompareAny((PetscObject)snes->jacobian_pre, &ismf, MATMFFD, MATSHELL, NULL));
    3320:     if (isdense) {
    3321:       PetscCall(DMSNESSetJacobian(dm, SNESComputeJacobianDefault, NULL));
    3322:     } else if (!ismf) {
    3323:       PetscCall(DMSNESSetJacobian(dm, SNESComputeJacobianDefaultColor, NULL));
    3324:     }
    3325:   }
    3326:   PetscFunctionReturn(PETSC_SUCCESS);
    3327: }

    3329: /*@
    3330:   SNESSetUp - Sets up the internal data structures for the later use
    3331:   of a nonlinear solver `SNESSolve()`.

    3333:   Collective

    3335:   Input Parameter:
    3336: . snes - the `SNES` context

    3338:   Level: advanced

    3340:   Note:
    3341:   For basic use of the `SNES` solvers the user does not need to explicitly call
    3342:   `SNESSetUp()`, since these actions will automatically occur during
    3343:   the call to `SNESSolve()`.  However, if one wishes to control this
    3344:   phase separately, `SNESSetUp()` should be called after `SNESCreate()`
    3345:   and optional routines of the form SNESSetXXX(), but before `SNESSolve()`.

    3347: .seealso: [](ch_snes), `SNES`, `SNESCreate()`, `SNESSolve()`, `SNESDestroy()`, `SNESSetFromOptions()`
    3348: @*/
    3349: PetscErrorCode SNESSetUp(SNES snes)
    3350: {
    3351:   DM             dm;
    3352:   DMSNES         sdm;
    3353:   SNESLineSearch linesearch, pclinesearch;
    3354:   void          *lsprectx, *lspostctx;
    3355:   PetscBool      mf_operator, mf;
    3356:   Vec            f, fpc;
    3357:   void          *funcctx;
    3358:   void          *jacctx, *appctx;
    3359:   Mat            j, jpre;
    3360:   PetscErrorCode (*precheck)(SNESLineSearch, Vec, Vec, PetscBool *, void *);
    3361:   PetscErrorCode (*postcheck)(SNESLineSearch, Vec, Vec, Vec, PetscBool *, PetscBool *, void *);
    3362:   SNESFunctionFn *func;
    3363:   SNESJacobianFn *jac;

    3365:   PetscFunctionBegin;
    3367:   if (snes->setupcalled) PetscFunctionReturn(PETSC_SUCCESS);
    3368:   PetscCall(PetscLogEventBegin(SNES_SetUp, snes, 0, 0, 0));

    3370:   if (!((PetscObject)snes)->type_name) PetscCall(SNESSetType(snes, SNESNEWTONLS));

    3372:   PetscCall(SNESGetFunction(snes, &snes->vec_func, NULL, NULL));

    3374:   PetscCall(SNESGetDM(snes, &dm));
    3375:   PetscCall(DMGetDMSNES(dm, &sdm));
    3376:   PetscCall(SNESSetDefaultComputeJacobian(snes));

    3378:   if (!snes->vec_func) PetscCall(DMCreateGlobalVector(dm, &snes->vec_func));

    3380:   if (!snes->ksp) PetscCall(SNESGetKSP(snes, &snes->ksp));

    3382:   if (snes->linesearch) {
    3383:     PetscCall(SNESGetLineSearch(snes, &snes->linesearch));
    3384:     PetscCall(SNESLineSearchSetFunction(snes->linesearch, SNESComputeFunction));
    3385:   }

    3387:   PetscCall(SNESGetUseMatrixFree(snes, &mf_operator, &mf));
    3388:   if (snes->npc && snes->npcside == PC_LEFT) {
    3389:     snes->mf          = PETSC_TRUE;
    3390:     snes->mf_operator = PETSC_FALSE;
    3391:   }

    3393:   if (snes->npc) {
    3394:     /* copy the DM over */
    3395:     PetscCall(SNESGetDM(snes, &dm));
    3396:     PetscCall(SNESSetDM(snes->npc, dm));

    3398:     PetscCall(SNESGetFunction(snes, &f, &func, &funcctx));
    3399:     PetscCall(VecDuplicate(f, &fpc));
    3400:     PetscCall(SNESSetFunction(snes->npc, fpc, func, funcctx));
    3401:     PetscCall(SNESGetJacobian(snes, &j, &jpre, &jac, &jacctx));
    3402:     PetscCall(SNESSetJacobian(snes->npc, j, jpre, jac, jacctx));
    3403:     PetscCall(SNESGetApplicationContext(snes, &appctx));
    3404:     PetscCall(SNESSetApplicationContext(snes->npc, appctx));
    3405:     PetscCall(SNESSetUseMatrixFree(snes->npc, mf_operator, mf));
    3406:     PetscCall(VecDestroy(&fpc));

    3408:     /* copy the function pointers over */
    3409:     PetscCall(PetscObjectCopyFortranFunctionPointers((PetscObject)snes, (PetscObject)snes->npc));

    3411:     /* default to 1 iteration */
    3412:     PetscCall(SNESSetTolerances(snes->npc, 0.0, 0.0, 0.0, 1, snes->npc->max_funcs));
    3413:     if (snes->npcside == PC_RIGHT) {
    3414:       PetscCall(SNESSetNormSchedule(snes->npc, SNES_NORM_FINAL_ONLY));
    3415:     } else {
    3416:       PetscCall(SNESSetNormSchedule(snes->npc, SNES_NORM_NONE));
    3417:     }
    3418:     PetscCall(SNESSetFromOptions(snes->npc));

    3420:     /* copy the line search context over */
    3421:     if (snes->linesearch && snes->npc->linesearch) {
    3422:       PetscCall(SNESGetLineSearch(snes, &linesearch));
    3423:       PetscCall(SNESGetLineSearch(snes->npc, &pclinesearch));
    3424:       PetscCall(SNESLineSearchGetPreCheck(linesearch, &precheck, &lsprectx));
    3425:       PetscCall(SNESLineSearchGetPostCheck(linesearch, &postcheck, &lspostctx));
    3426:       PetscCall(SNESLineSearchSetPreCheck(pclinesearch, precheck, lsprectx));
    3427:       PetscCall(SNESLineSearchSetPostCheck(pclinesearch, postcheck, lspostctx));
    3428:       PetscCall(PetscObjectCopyFortranFunctionPointers((PetscObject)linesearch, (PetscObject)pclinesearch));
    3429:     }
    3430:   }
    3431:   if (snes->mf) PetscCall(SNESSetUpMatrixFree_Private(snes, snes->mf_operator, snes->mf_version));
    3432:   if (snes->ops->usercompute && !snes->ctx) PetscCallBack("SNES callback compute application context", (*snes->ops->usercompute)(snes, &snes->ctx));

    3434:   snes->jac_iter = 0;
    3435:   snes->pre_iter = 0;

    3437:   PetscTryTypeMethod(snes, setup);

    3439:   PetscCall(SNESSetDefaultComputeJacobian(snes));

    3441:   if (snes->npc && snes->npcside == PC_LEFT) {
    3442:     if (snes->functype == SNES_FUNCTION_PRECONDITIONED) {
    3443:       if (snes->linesearch) {
    3444:         PetscCall(SNESGetLineSearch(snes, &linesearch));
    3445:         PetscCall(SNESLineSearchSetFunction(linesearch, SNESComputeFunctionDefaultNPC));
    3446:       }
    3447:     }
    3448:   }
    3449:   PetscCall(PetscLogEventEnd(SNES_SetUp, snes, 0, 0, 0));
    3450:   snes->setupcalled = PETSC_TRUE;
    3451:   PetscFunctionReturn(PETSC_SUCCESS);
    3452: }

    3454: /*@
    3455:   SNESReset - Resets a `SNES` context to the state it was in before `SNESSetUp()` was called and removes any allocated `Vec` and `Mat` from its data structures

    3457:   Collective

    3459:   Input Parameter:
    3460: . snes - the nonlinear iterative solver context obtained from `SNESCreate()`

    3462:   Level: intermediate

    3464:   Notes:
    3465:   Any options set on the `SNES` object, including those set with `SNESSetFromOptions()` remain.

    3467:   Call this if you wish to reuse a `SNES` but with different size vectors

    3469:   Also calls the application context destroy routine set with `SNESSetComputeApplicationContext()`

    3471: .seealso: [](ch_snes), `SNES`, `SNESDestroy()`, `SNESCreate()`, `SNESSetUp()`, `SNESSolve()`
    3472: @*/
    3473: PetscErrorCode SNESReset(SNES snes)
    3474: {
    3475:   PetscFunctionBegin;
    3477:   if (snes->ops->ctxdestroy && snes->ctx) {
    3478:     PetscCallBack("SNES callback destroy application context", (*snes->ops->ctxdestroy)(&snes->ctx));
    3479:     snes->ctx = NULL;
    3480:   }
    3481:   if (snes->npc) PetscCall(SNESReset(snes->npc));

    3483:   PetscTryTypeMethod(snes, reset);
    3484:   if (snes->ksp) PetscCall(KSPReset(snes->ksp));

    3486:   if (snes->linesearch) PetscCall(SNESLineSearchReset(snes->linesearch));

    3488:   PetscCall(VecDestroy(&snes->vec_rhs));
    3489:   PetscCall(VecDestroy(&snes->vec_sol));
    3490:   PetscCall(VecDestroy(&snes->vec_sol_update));
    3491:   PetscCall(VecDestroy(&snes->vec_func));
    3492:   PetscCall(MatDestroy(&snes->jacobian));
    3493:   PetscCall(MatDestroy(&snes->jacobian_pre));
    3494:   PetscCall(MatDestroy(&snes->picard));
    3495:   PetscCall(VecDestroyVecs(snes->nwork, &snes->work));
    3496:   PetscCall(VecDestroyVecs(snes->nvwork, &snes->vwork));

    3498:   snes->alwayscomputesfinalresidual = PETSC_FALSE;

    3500:   snes->nwork = snes->nvwork = 0;
    3501:   snes->setupcalled          = PETSC_FALSE;
    3502:   PetscFunctionReturn(PETSC_SUCCESS);
    3503: }

    3505: /*@
    3506:   SNESConvergedReasonViewCancel - Clears all the reason view functions for a `SNES` object provided with `SNESConvergedReasonViewSet()` also
    3507:   removes the default viewer.

    3509:   Collective

    3511:   Input Parameter:
    3512: . snes - the nonlinear iterative solver context obtained from `SNESCreate()`

    3514:   Level: intermediate

    3516: .seealso: [](ch_snes), `SNES`, `SNESCreate()`, `SNESDestroy()`, `SNESReset()`, `SNESConvergedReasonViewSet()`
    3517: @*/
    3518: PetscErrorCode SNESConvergedReasonViewCancel(SNES snes)
    3519: {
    3520:   PetscInt i;

    3522:   PetscFunctionBegin;
    3524:   for (i = 0; i < snes->numberreasonviews; i++) {
    3525:     if (snes->reasonviewdestroy[i]) PetscCall((*snes->reasonviewdestroy[i])(&snes->reasonviewcontext[i]));
    3526:   }
    3527:   snes->numberreasonviews = 0;
    3528:   PetscCall(PetscViewerDestroy(&snes->convergedreasonviewer));
    3529:   PetscFunctionReturn(PETSC_SUCCESS);
    3530: }

    3532: /*@
    3533:   SNESDestroy - Destroys the nonlinear solver context that was created
    3534:   with `SNESCreate()`.

    3536:   Collective

    3538:   Input Parameter:
    3539: . snes - the `SNES` context

    3541:   Level: beginner

    3543: .seealso: [](ch_snes), `SNES`, `SNESCreate()`, `SNESSolve()`
    3544: @*/
    3545: PetscErrorCode SNESDestroy(SNES *snes)
    3546: {
    3547:   DM dm;

    3549:   PetscFunctionBegin;
    3550:   if (!*snes) PetscFunctionReturn(PETSC_SUCCESS);
    3552:   if (--((PetscObject)*snes)->refct > 0) {
    3553:     *snes = NULL;
    3554:     PetscFunctionReturn(PETSC_SUCCESS);
    3555:   }

    3557:   PetscCall(SNESReset(*snes));
    3558:   PetscCall(SNESDestroy(&(*snes)->npc));

    3560:   /* if memory was published with SAWs then destroy it */
    3561:   PetscCall(PetscObjectSAWsViewOff((PetscObject)*snes));
    3562:   PetscTryTypeMethod(*snes, destroy);

    3564:   dm = (*snes)->dm;
    3565:   while (dm) {
    3566:     PetscCall(DMCoarsenHookRemove(dm, DMCoarsenHook_SNESVecSol, DMRestrictHook_SNESVecSol, *snes));
    3567:     PetscCall(DMGetCoarseDM(dm, &dm));
    3568:   }

    3570:   PetscCall(DMDestroy(&(*snes)->dm));
    3571:   PetscCall(KSPDestroy(&(*snes)->ksp));
    3572:   PetscCall(SNESLineSearchDestroy(&(*snes)->linesearch));

    3574:   PetscCall(PetscFree((*snes)->kspconvctx));
    3575:   if ((*snes)->ops->convergeddestroy) PetscCall((*(*snes)->ops->convergeddestroy)((*snes)->cnvP));
    3576:   if ((*snes)->conv_hist_alloc) PetscCall(PetscFree2((*snes)->conv_hist, (*snes)->conv_hist_its));
    3577:   PetscCall(SNESMonitorCancel(*snes));
    3578:   PetscCall(SNESConvergedReasonViewCancel(*snes));
    3579:   PetscCall(PetscHeaderDestroy(snes));
    3580:   PetscFunctionReturn(PETSC_SUCCESS);
    3581: }

    3583: /* ----------- Routines to set solver parameters ---------- */

    3585: /*@
    3586:   SNESSetLagPreconditioner - Sets when the preconditioner is rebuilt in the nonlinear solve `SNESSolve()`.

    3588:   Logically Collective

    3590:   Input Parameters:
    3591: + snes - the `SNES` context
    3592: - lag  - 1 means rebuild every time the Jacobian is computed within a single nonlinear solve, 2 means every second time
    3593:          the Jacobian is built etc. -2 indicates rebuild preconditioner at next chance but then never rebuild after that

    3595:   Options Database Keys:
    3596: + -snes_lag_jacobian_persists <true,false>       - sets the persistence through multiple `SNESSolve()`
    3597: . -snes_lag_jacobian <-2,1,2,...>                - sets the lag
    3598: . -snes_lag_preconditioner_persists <true,false> - sets the persistence through multiple `SNESSolve()`
    3599: - -snes_lag_preconditioner <-2,1,2,...>          - sets the lag

    3601:   Level: intermediate

    3603:   Notes:
    3604:   The default is 1

    3606:   The preconditioner is ALWAYS built in the first iteration of a nonlinear solve unless lag is -1 or `SNESSetLagPreconditionerPersists()` was called

    3608:   `SNESSetLagPreconditionerPersists()` allows using the same uniform lagging (for example every second linear solve) across multiple nonlinear solves.

    3610: .seealso: [](ch_snes), `SNESGetLagPreconditioner()`, `SNESSetLagJacobian()`, `SNESGetLagJacobian()`, `SNESSetLagPreconditionerPersists()`,
    3611:           `SNESSetLagJacobianPersists()`, `SNES`, `SNESSolve()`
    3612: @*/
    3613: PetscErrorCode SNESSetLagPreconditioner(SNES snes, PetscInt lag)
    3614: {
    3615:   PetscFunctionBegin;
    3617:   PetscCheck(lag >= -2, PETSC_COMM_SELF, PETSC_ERR_ARG_OUTOFRANGE, "Lag must be -2, -1, 1 or greater");
    3618:   PetscCheck(lag, PETSC_COMM_SELF, PETSC_ERR_ARG_OUTOFRANGE, "Lag cannot be 0");
    3620:   snes->lagpreconditioner = lag;
    3621:   PetscFunctionReturn(PETSC_SUCCESS);
    3622: }

    3624: /*@
    3625:   SNESSetGridSequence - sets the number of steps of grid sequencing that `SNES` will do

    3627:   Logically Collective

    3629:   Input Parameters:
    3630: + snes  - the `SNES` context
    3631: - steps - the number of refinements to do, defaults to 0

    3633:   Options Database Key:
    3634: . -snes_grid_sequence <steps> - Use grid sequencing to generate initial guess

    3636:   Level: intermediate

    3638:   Notes:
    3639:   Once grid sequencing is turned on `SNESSolve()` will automatically perform the solve on each grid refinement.

    3641:   Use `SNESGetSolution()` to extract the fine grid solution after grid sequencing.

    3643: .seealso: [](ch_snes), `SNES`, `SNESGetLagPreconditioner()`, `SNESSetLagJacobian()`, `SNESGetLagJacobian()`, `SNESGetGridSequence()`,
    3644:           `SNESSetDM()`, `SNESSolve()`
    3645: @*/
    3646: PetscErrorCode SNESSetGridSequence(SNES snes, PetscInt steps)
    3647: {
    3648:   PetscFunctionBegin;
    3651:   snes->gridsequence = steps;
    3652:   PetscFunctionReturn(PETSC_SUCCESS);
    3653: }

    3655: /*@
    3656:   SNESGetGridSequence - gets the number of steps of grid sequencing that `SNES` will do

    3658:   Logically Collective

    3660:   Input Parameter:
    3661: . snes - the `SNES` context

    3663:   Output Parameter:
    3664: . steps - the number of refinements to do, defaults to 0

    3666:   Level: intermediate

    3668: .seealso: [](ch_snes), `SNESGetLagPreconditioner()`, `SNESSetLagJacobian()`, `SNESGetLagJacobian()`, `SNESSetGridSequence()`
    3669: @*/
    3670: PetscErrorCode SNESGetGridSequence(SNES snes, PetscInt *steps)
    3671: {
    3672:   PetscFunctionBegin;
    3674:   *steps = snes->gridsequence;
    3675:   PetscFunctionReturn(PETSC_SUCCESS);
    3676: }

    3678: /*@
    3679:   SNESGetLagPreconditioner - Return how often the preconditioner is rebuilt

    3681:   Not Collective

    3683:   Input Parameter:
    3684: . snes - the `SNES` context

    3686:   Output Parameter:
    3687: . lag - -1 indicates NEVER rebuild, 1 means rebuild every time the Jacobian is computed within a single nonlinear solve, 2 means every second time
    3688:          the Jacobian is built etc. -2 indicates rebuild preconditioner at next chance but then never rebuild after that

    3690:   Level: intermediate

    3692:   Notes:
    3693:   The default is 1

    3695:   The preconditioner is ALWAYS built in the first iteration of a nonlinear solve unless lag is -1

    3697: .seealso: [](ch_snes), `SNES`, `SNESSetLagPreconditioner()`, `SNESSetLagJacobianPersists()`, `SNESSetLagPreconditionerPersists()`
    3698: @*/
    3699: PetscErrorCode SNESGetLagPreconditioner(SNES snes, PetscInt *lag)
    3700: {
    3701:   PetscFunctionBegin;
    3703:   *lag = snes->lagpreconditioner;
    3704:   PetscFunctionReturn(PETSC_SUCCESS);
    3705: }

    3707: /*@
    3708:   SNESSetLagJacobian - Set when the Jacobian is rebuilt in the nonlinear solve. See `SNESSetLagPreconditioner()` for determining how
    3709:   often the preconditioner is rebuilt.

    3711:   Logically Collective

    3713:   Input Parameters:
    3714: + snes - the `SNES` context
    3715: - lag  - -1 indicates NEVER rebuild, 1 means rebuild every time the Jacobian is computed within a single nonlinear solve, 2 means every second time
    3716:          the Jacobian is built etc. -2 means rebuild at next chance but then never again

    3718:   Options Database Keys:
    3719: + -snes_lag_jacobian_persists <true,false>       - sets the persistence through multiple SNES solves
    3720: . -snes_lag_jacobian <-2,1,2,...>                - sets the lag
    3721: . -snes_lag_preconditioner_persists <true,false> - sets the persistence through multiple SNES solves
    3722: - -snes_lag_preconditioner <-2,1,2,...>          - sets the lag.

    3724:   Level: intermediate

    3726:   Notes:
    3727:   The default is 1

    3729:   The Jacobian is ALWAYS built in the first iteration of a nonlinear solve unless lag is -1

    3731:   If  -1 is used before the very first nonlinear solve the CODE WILL FAIL! because no Jacobian is used, use -2 to indicate you want it recomputed
    3732:   at the next Newton step but never again (unless it is reset to another value)

    3734: .seealso: [](ch_snes), `SNES`, `SNESGetLagPreconditioner()`, `SNESSetLagPreconditioner()`, `SNESGetLagJacobianPersists()`, `SNESSetLagPreconditionerPersists()`
    3735: @*/
    3736: PetscErrorCode SNESSetLagJacobian(SNES snes, PetscInt lag)
    3737: {
    3738:   PetscFunctionBegin;
    3740:   PetscCheck(lag >= -2, PETSC_COMM_SELF, PETSC_ERR_ARG_OUTOFRANGE, "Lag must be -2, -1, 1 or greater");
    3741:   PetscCheck(lag, PETSC_COMM_SELF, PETSC_ERR_ARG_OUTOFRANGE, "Lag cannot be 0");
    3743:   snes->lagjacobian = lag;
    3744:   PetscFunctionReturn(PETSC_SUCCESS);
    3745: }

    3747: /*@
    3748:   SNESGetLagJacobian - Get how often the Jacobian is rebuilt. See `SNESGetLagPreconditioner()` to determine when the preconditioner is rebuilt

    3750:   Not Collective

    3752:   Input Parameter:
    3753: . snes - the `SNES` context

    3755:   Output Parameter:
    3756: . lag - -1 indicates NEVER rebuild, 1 means rebuild every time the Jacobian is computed within a single nonlinear solve, 2 means every second time
    3757:          the Jacobian is built etc.

    3759:   Level: intermediate

    3761:   Notes:
    3762:   The default is 1

    3764:   The jacobian is ALWAYS built in the first iteration of a nonlinear solve unless lag is -1 or `SNESSetLagJacobianPersists()` was called.

    3766: .seealso: [](ch_snes), `SNES`, `SNESSetLagJacobian()`, `SNESSetLagPreconditioner()`, `SNESGetLagPreconditioner()`, `SNESSetLagJacobianPersists()`, `SNESSetLagPreconditionerPersists()`

    3768: @*/
    3769: PetscErrorCode SNESGetLagJacobian(SNES snes, PetscInt *lag)
    3770: {
    3771:   PetscFunctionBegin;
    3773:   *lag = snes->lagjacobian;
    3774:   PetscFunctionReturn(PETSC_SUCCESS);
    3775: }

    3777: /*@
    3778:   SNESSetLagJacobianPersists - Set whether or not the Jacobian lagging persists through multiple nonlinear solves

    3780:   Logically collective

    3782:   Input Parameters:
    3783: + snes - the `SNES` context
    3784: - flg  - jacobian lagging persists if true

    3786:   Options Database Keys:
    3787: + -snes_lag_jacobian_persists <true,false>       - sets the persistence through multiple SNES solves
    3788: . -snes_lag_jacobian <-2,1,2,...>                - sets the lag
    3789: . -snes_lag_preconditioner_persists <true,false> - sets the persistence through multiple SNES solves
    3790: - -snes_lag_preconditioner <-2,1,2,...>          - sets the lag

    3792:   Level: advanced

    3794:   Notes:
    3795:   Normally when `SNESSetLagJacobian()` is used, the Jacobian is always rebuilt at the beginning of each new nonlinear solve, this removes that behavior

    3797:   This is useful both for nonlinear preconditioning, where it's appropriate to have the Jacobian be stale by
    3798:   several solves, and for implicit time-stepping, where Jacobian lagging in the inner nonlinear solve over several
    3799:   timesteps may present huge efficiency gains.

    3801: .seealso: [](ch_snes), `SNES`, `SNESSetLagPreconditionerPersists()`, `SNESSetLagJacobian()`, `SNESGetLagJacobian()`, `SNESGetNPC()`
    3802: @*/
    3803: PetscErrorCode SNESSetLagJacobianPersists(SNES snes, PetscBool flg)
    3804: {
    3805:   PetscFunctionBegin;
    3808:   snes->lagjac_persist = flg;
    3809:   PetscFunctionReturn(PETSC_SUCCESS);
    3810: }

    3812: /*@
    3813:   SNESSetLagPreconditionerPersists - Set whether or not the preconditioner lagging persists through multiple nonlinear solves

    3815:   Logically Collective

    3817:   Input Parameters:
    3818: + snes - the `SNES` context
    3819: - flg  - preconditioner lagging persists if true

    3821:   Options Database Keys:
    3822: + -snes_lag_jacobian_persists <true,false>       - sets the persistence through multiple SNES solves
    3823: . -snes_lag_jacobian <-2,1,2,...>                - sets the lag
    3824: . -snes_lag_preconditioner_persists <true,false> - sets the persistence through multiple SNES solves
    3825: - -snes_lag_preconditioner <-2,1,2,...>          - sets the lag

    3827:   Level: developer

    3829:   Notes:
    3830:   Normally when `SNESSetLagPreconditioner()` is used, the preconditioner is always rebuilt at the beginning of each new nonlinear solve, this removes that behavior

    3832:   This is useful both for nonlinear preconditioning, where it's appropriate to have the preconditioner be stale
    3833:   by several solves, and for implicit time-stepping, where preconditioner lagging in the inner nonlinear solve over
    3834:   several timesteps may present huge efficiency gains.

    3836: .seealso: [](ch_snes), `SNES`, `SNESSetLagJacobianPersists()`, `SNESSetLagJacobian()`, `SNESGetLagJacobian()`, `SNESGetNPC()`, `SNESSetLagPreconditioner()`
    3837: @*/
    3838: PetscErrorCode SNESSetLagPreconditionerPersists(SNES snes, PetscBool flg)
    3839: {
    3840:   PetscFunctionBegin;
    3843:   snes->lagpre_persist = flg;
    3844:   PetscFunctionReturn(PETSC_SUCCESS);
    3845: }

    3847: /*@
    3848:   SNESSetForceIteration - force `SNESSolve()` to take at least one iteration regardless of the initial residual norm

    3850:   Logically Collective

    3852:   Input Parameters:
    3853: + snes  - the `SNES` context
    3854: - force - `PETSC_TRUE` require at least one iteration

    3856:   Options Database Key:
    3857: . -snes_force_iteration <force> - Sets forcing an iteration

    3859:   Level: intermediate

    3861:   Note:
    3862:   This is used sometimes with `TS` to prevent `TS` from detecting a false steady state solution

    3864: .seealso: [](ch_snes), `SNES`, `TS`, `SNESSetDivergenceTolerance()`
    3865: @*/
    3866: PetscErrorCode SNESSetForceIteration(SNES snes, PetscBool force)
    3867: {
    3868:   PetscFunctionBegin;
    3870:   snes->forceiteration = force;
    3871:   PetscFunctionReturn(PETSC_SUCCESS);
    3872: }

    3874: /*@
    3875:   SNESGetForceIteration - Check whether or not `SNESSolve()` take at least one iteration regardless of the initial residual norm

    3877:   Logically Collective

    3879:   Input Parameter:
    3880: . snes - the `SNES` context

    3882:   Output Parameter:
    3883: . force - `PETSC_TRUE` requires at least one iteration.

    3885:   Level: intermediate

    3887: .seealso: [](ch_snes), `SNES`, `SNESSetForceIteration()`, `SNESSetDivergenceTolerance()`
    3888: @*/
    3889: PetscErrorCode SNESGetForceIteration(SNES snes, PetscBool *force)
    3890: {
    3891:   PetscFunctionBegin;
    3893:   *force = snes->forceiteration;
    3894:   PetscFunctionReturn(PETSC_SUCCESS);
    3895: }

    3897: /*@
    3898:   SNESSetTolerances - Sets various parameters used in `SNES` convergence tests.

    3900:   Logically Collective

    3902:   Input Parameters:
    3903: + snes   - the `SNES` context
    3904: . abstol - the absolute convergence tolerance, $ F(x^n) \le abstol $
    3905: . rtol   - the relative convergence tolerance, $ F(x^n) \le reltol * F(x^0) $
    3906: . stol   - convergence tolerance in terms of the norm of the change in the solution between steps,  || delta x || < stol*|| x ||
    3907: . maxit  - the maximum number of iterations allowed in the solver, default 50.
    3908: - maxf   - the maximum number of function evaluations allowed in the solver (use `PETSC_UNLIMITED` indicates no limit), default 10,000

    3910:   Options Database Keys:
    3911: + -snes_atol <abstol>    - Sets `abstol`
    3912: . -snes_rtol <rtol>      - Sets `rtol`
    3913: . -snes_stol <stol>      - Sets `stol`
    3914: . -snes_max_it <maxit>   - Sets `maxit`
    3915: - -snes_max_funcs <maxf> - Sets `maxf` (use `unlimited` to have no maximum)

    3917:   Level: intermediate

    3919:   Note:
    3920:   All parameters must be non-negative

    3922:   Use `PETSC_CURRENT` to retain the current value of any parameter and `PETSC_DETERMINE` to use the default value for the given `SNES`.
    3923:   The default value is the value in the object when its type is set.

    3925:   Use `PETSC_UNLIMITED` on `maxit` or `maxf` to indicate there is no bound on the number of iterations or number of function evaluations.

    3927:   Fortran Note:
    3928:   Use `PETSC_CURRENT_INTEGER`, `PETSC_CURRENT_REAL`, `PETSC_UNLIMITED_INTEGER`, `PETSC_DETERMINE_INTEGER`, or `PETSC_DETERMINE_REAL`

    3930: .seealso: [](ch_snes), `SNESSolve()`, `SNES`, `SNESSetDivergenceTolerance()`, `SNESSetForceIteration()`
    3931: @*/
    3932: PetscErrorCode SNESSetTolerances(SNES snes, PetscReal abstol, PetscReal rtol, PetscReal stol, PetscInt maxit, PetscInt maxf)
    3933: {
    3934:   PetscFunctionBegin;

    3942:   if (abstol == (PetscReal)PETSC_DETERMINE) {
    3943:     snes->abstol = snes->default_abstol;
    3944:   } else if (abstol != (PetscReal)PETSC_CURRENT) {
    3945:     PetscCheck(abstol >= 0.0, PetscObjectComm((PetscObject)snes), PETSC_ERR_ARG_OUTOFRANGE, "Absolute tolerance %g must be non-negative", (double)abstol);
    3946:     snes->abstol = abstol;
    3947:   }

    3949:   if (rtol == (PetscReal)PETSC_DETERMINE) {
    3950:     snes->rtol = snes->default_rtol;
    3951:   } else if (rtol != (PetscReal)PETSC_CURRENT) {
    3952:     PetscCheck(rtol >= 0.0 && 1.0 > rtol, PetscObjectComm((PetscObject)snes), PETSC_ERR_ARG_OUTOFRANGE, "Relative tolerance %g must be non-negative and less than 1.0", (double)rtol);
    3953:     snes->rtol = rtol;
    3954:   }

    3956:   if (stol == (PetscReal)PETSC_DETERMINE) {
    3957:     snes->stol = snes->default_stol;
    3958:   } else if (stol != (PetscReal)PETSC_CURRENT) {
    3959:     PetscCheck(stol >= 0.0, PetscObjectComm((PetscObject)snes), PETSC_ERR_ARG_OUTOFRANGE, "Step tolerance %g must be non-negative", (double)stol);
    3960:     snes->stol = stol;
    3961:   }

    3963:   if (maxit == PETSC_DETERMINE) {
    3964:     snes->max_its = snes->default_max_its;
    3965:   } else if (maxit == PETSC_UNLIMITED) {
    3966:     snes->max_its = PETSC_INT_MAX;
    3967:   } else if (maxit != PETSC_CURRENT) {
    3968:     PetscCheck(maxit >= 0, PetscObjectComm((PetscObject)snes), PETSC_ERR_ARG_OUTOFRANGE, "Maximum number of iterations %" PetscInt_FMT " must be non-negative", maxit);
    3969:     snes->max_its = maxit;
    3970:   }

    3972:   if (maxf == PETSC_DETERMINE) {
    3973:     snes->max_funcs = snes->default_max_funcs;
    3974:   } else if (maxf == PETSC_UNLIMITED || maxf == -1) {
    3975:     snes->max_funcs = PETSC_UNLIMITED;
    3976:   } else if (maxf != PETSC_CURRENT) {
    3977:     PetscCheck(maxf >= 0, PetscObjectComm((PetscObject)snes), PETSC_ERR_ARG_OUTOFRANGE, "Maximum number of function evaluations %" PetscInt_FMT " must be nonnegative", maxf);
    3978:     snes->max_funcs = maxf;
    3979:   }
    3980:   PetscFunctionReturn(PETSC_SUCCESS);
    3981: }

    3983: /*@
    3984:   SNESSetDivergenceTolerance - Sets the divergence tolerance used for the `SNES` divergence test.

    3986:   Logically Collective

    3988:   Input Parameters:
    3989: + snes   - the `SNES` context
    3990: - divtol - the divergence tolerance. Use `PETSC_UNLIMITED` to deactivate the test. If the residual norm $ F(x^n) \ge divtol * F(x^0) $ the solver
    3991:            is stopped due to divergence.

    3993:   Options Database Key:
    3994: . -snes_divergence_tolerance <divtol> - Sets `divtol`

    3996:   Level: intermediate

    3998:   Notes:
    3999:   Use `PETSC_DETERMINE` to use the default value from when the object's type was set.

    4001:   Fortran Note:
    4002:   Use ``PETSC_DETERMINE_REAL` or `PETSC_UNLIMITED_REAL`

    4004: .seealso: [](ch_snes), `SNES`, `SNESSolve()`, `SNESSetTolerances()`, `SNESGetDivergenceTolerance()`
    4005: @*/
    4006: PetscErrorCode SNESSetDivergenceTolerance(SNES snes, PetscReal divtol)
    4007: {
    4008:   PetscFunctionBegin;

    4012:   if (divtol == (PetscReal)PETSC_DETERMINE) {
    4013:     snes->divtol = snes->default_divtol;
    4014:   } else if (divtol == (PetscReal)PETSC_UNLIMITED || divtol == -1) {
    4015:     snes->divtol = PETSC_UNLIMITED;
    4016:   } else if (divtol != (PetscReal)PETSC_CURRENT) {
    4017:     PetscCheck(divtol >= 1.0, PetscObjectComm((PetscObject)snes), PETSC_ERR_ARG_OUTOFRANGE, "Divergence tolerance %g must be greater than 1.0", (double)divtol);
    4018:     snes->divtol = divtol;
    4019:   }
    4020:   PetscFunctionReturn(PETSC_SUCCESS);
    4021: }

    4023: /*@
    4024:   SNESGetTolerances - Gets various parameters used in `SNES` convergence tests.

    4026:   Not Collective

    4028:   Input Parameter:
    4029: . snes - the `SNES` context

    4031:   Output Parameters:
    4032: + atol  - the absolute convergence tolerance
    4033: . rtol  - the relative convergence tolerance
    4034: . stol  - convergence tolerance in terms of the norm of the change in the solution between steps
    4035: . maxit - the maximum number of iterations allowed
    4036: - maxf  - the maximum number of function evaluations allowed, `PETSC_UNLIMITED` indicates no bound

    4038:   Level: intermediate

    4040:   Notes:
    4041:   See `SNESSetTolerances()` for details on the parameters.

    4043:   The user can specify `NULL` for any parameter that is not needed.

    4045: .seealso: [](ch_snes), `SNES`, `SNESSetTolerances()`
    4046: @*/
    4047: PetscErrorCode SNESGetTolerances(SNES snes, PetscReal *atol, PetscReal *rtol, PetscReal *stol, PetscInt *maxit, PetscInt *maxf)
    4048: {
    4049:   PetscFunctionBegin;
    4051:   if (atol) *atol = snes->abstol;
    4052:   if (rtol) *rtol = snes->rtol;
    4053:   if (stol) *stol = snes->stol;
    4054:   if (maxit) *maxit = snes->max_its;
    4055:   if (maxf) *maxf = snes->max_funcs;
    4056:   PetscFunctionReturn(PETSC_SUCCESS);
    4057: }

    4059: /*@
    4060:   SNESGetDivergenceTolerance - Gets divergence tolerance used in divergence test.

    4062:   Not Collective

    4064:   Input Parameters:
    4065: + snes   - the `SNES` context
    4066: - divtol - divergence tolerance

    4068:   Level: intermediate

    4070: .seealso: [](ch_snes), `SNES`, `SNESSetDivergenceTolerance()`
    4071: @*/
    4072: PetscErrorCode SNESGetDivergenceTolerance(SNES snes, PetscReal *divtol)
    4073: {
    4074:   PetscFunctionBegin;
    4076:   if (divtol) *divtol = snes->divtol;
    4077:   PetscFunctionReturn(PETSC_SUCCESS);
    4078: }

    4080: PETSC_INTERN PetscErrorCode SNESMonitorRange_Private(SNES, PetscInt, PetscReal *);

    4082: PetscErrorCode SNESMonitorLGRange(SNES snes, PetscInt n, PetscReal rnorm, void *monctx)
    4083: {
    4084:   PetscDrawLG      lg;
    4085:   PetscReal        x, y, per;
    4086:   PetscViewer      v = (PetscViewer)monctx;
    4087:   static PetscReal prev; /* should be in the context */
    4088:   PetscDraw        draw;

    4090:   PetscFunctionBegin;
    4092:   PetscCall(PetscViewerDrawGetDrawLG(v, 0, &lg));
    4093:   if (!n) PetscCall(PetscDrawLGReset(lg));
    4094:   PetscCall(PetscDrawLGGetDraw(lg, &draw));
    4095:   PetscCall(PetscDrawSetTitle(draw, "Residual norm"));
    4096:   x = (PetscReal)n;
    4097:   if (rnorm > 0.0) y = PetscLog10Real(rnorm);
    4098:   else y = -15.0;
    4099:   PetscCall(PetscDrawLGAddPoint(lg, &x, &y));
    4100:   if (n < 20 || !(n % 5) || snes->reason) {
    4101:     PetscCall(PetscDrawLGDraw(lg));
    4102:     PetscCall(PetscDrawLGSave(lg));
    4103:   }

    4105:   PetscCall(PetscViewerDrawGetDrawLG(v, 1, &lg));
    4106:   if (!n) PetscCall(PetscDrawLGReset(lg));
    4107:   PetscCall(PetscDrawLGGetDraw(lg, &draw));
    4108:   PetscCall(PetscDrawSetTitle(draw, "% elements > .2*max element"));
    4109:   PetscCall(SNESMonitorRange_Private(snes, n, &per));
    4110:   x = (PetscReal)n;
    4111:   y = 100.0 * per;
    4112:   PetscCall(PetscDrawLGAddPoint(lg, &x, &y));
    4113:   if (n < 20 || !(n % 5) || snes->reason) {
    4114:     PetscCall(PetscDrawLGDraw(lg));
    4115:     PetscCall(PetscDrawLGSave(lg));
    4116:   }

    4118:   PetscCall(PetscViewerDrawGetDrawLG(v, 2, &lg));
    4119:   if (!n) {
    4120:     prev = rnorm;
    4121:     PetscCall(PetscDrawLGReset(lg));
    4122:   }
    4123:   PetscCall(PetscDrawLGGetDraw(lg, &draw));
    4124:   PetscCall(PetscDrawSetTitle(draw, "(norm -oldnorm)/oldnorm"));
    4125:   x = (PetscReal)n;
    4126:   y = (prev - rnorm) / prev;
    4127:   PetscCall(PetscDrawLGAddPoint(lg, &x, &y));
    4128:   if (n < 20 || !(n % 5) || snes->reason) {
    4129:     PetscCall(PetscDrawLGDraw(lg));
    4130:     PetscCall(PetscDrawLGSave(lg));
    4131:   }

    4133:   PetscCall(PetscViewerDrawGetDrawLG(v, 3, &lg));
    4134:   if (!n) PetscCall(PetscDrawLGReset(lg));
    4135:   PetscCall(PetscDrawLGGetDraw(lg, &draw));
    4136:   PetscCall(PetscDrawSetTitle(draw, "(norm -oldnorm)/oldnorm*(% > .2 max)"));
    4137:   x = (PetscReal)n;
    4138:   y = (prev - rnorm) / (prev * per);
    4139:   if (n > 2) { /*skip initial crazy value */
    4140:     PetscCall(PetscDrawLGAddPoint(lg, &x, &y));
    4141:   }
    4142:   if (n < 20 || !(n % 5) || snes->reason) {
    4143:     PetscCall(PetscDrawLGDraw(lg));
    4144:     PetscCall(PetscDrawLGSave(lg));
    4145:   }
    4146:   prev = rnorm;
    4147:   PetscFunctionReturn(PETSC_SUCCESS);
    4148: }

    4150: /*@
    4151:   SNESConverged - Run the convergence test and update the `SNESConvergedReason`.

    4153:   Collective

    4155:   Input Parameters:
    4156: + snes  - the `SNES` context
    4157: . it    - current iteration
    4158: . xnorm - 2-norm of current iterate
    4159: . snorm - 2-norm of current step
    4160: - fnorm - 2-norm of function

    4162:   Level: developer

    4164:   Note:
    4165:   This routine is called by the `SNESSolve()` implementations.
    4166:   It does not typically need to be called by the user.

    4168: .seealso: [](ch_snes), `SNES`, `SNESSolve`, `SNESSetConvergenceTest()`
    4169: @*/
    4170: PetscErrorCode SNESConverged(SNES snes, PetscInt it, PetscReal xnorm, PetscReal snorm, PetscReal fnorm)
    4171: {
    4172:   PetscFunctionBegin;
    4173:   if (!snes->reason) {
    4174:     if (snes->normschedule == SNES_NORM_ALWAYS) PetscUseTypeMethod(snes, converged, it, xnorm, snorm, fnorm, &snes->reason, snes->cnvP);
    4175:     if (it == snes->max_its && !snes->reason) {
    4176:       if (snes->normschedule == SNES_NORM_ALWAYS) {
    4177:         PetscCall(PetscInfo(snes, "Maximum number of iterations has been reached: %" PetscInt_FMT "\n", snes->max_its));
    4178:         snes->reason = SNES_DIVERGED_MAX_IT;
    4179:       } else snes->reason = SNES_CONVERGED_ITS;
    4180:     }
    4181:   }
    4182:   PetscFunctionReturn(PETSC_SUCCESS);
    4183: }

    4185: /*@
    4186:   SNESMonitor - runs any `SNES` monitor routines provided with `SNESMonitor()` or the options database

    4188:   Collective

    4190:   Input Parameters:
    4191: + snes  - nonlinear solver context obtained from `SNESCreate()`
    4192: . iter  - current iteration number
    4193: - rnorm - current relative norm of the residual

    4195:   Level: developer

    4197:   Note:
    4198:   This routine is called by the `SNESSolve()` implementations.
    4199:   It does not typically need to be called by the user.

    4201: .seealso: [](ch_snes), `SNES`, `SNESMonitorSet()`
    4202: @*/
    4203: PetscErrorCode SNESMonitor(SNES snes, PetscInt iter, PetscReal rnorm)
    4204: {
    4205:   PetscInt i, n = snes->numbermonitors;

    4207:   PetscFunctionBegin;
    4208:   PetscCall(VecLockReadPush(snes->vec_sol));
    4209:   for (i = 0; i < n; i++) PetscCall((*snes->monitor[i])(snes, iter, rnorm, snes->monitorcontext[i]));
    4210:   PetscCall(VecLockReadPop(snes->vec_sol));
    4211:   PetscFunctionReturn(PETSC_SUCCESS);
    4212: }

    4214: /* ------------ Routines to set performance monitoring options ----------- */

    4216: /*MC
    4217:     SNESMonitorFunction - functional form passed to `SNESMonitorSet()` to monitor convergence of nonlinear solver

    4219:      Synopsis:
    4220: #include <petscsnes.h>
    4221:     PetscErrorCode SNESMonitorFunction(SNES snes, PetscInt its, PetscReal norm, void *mctx)

    4223:      Collective

    4225:     Input Parameters:
    4226: +    snes - the `SNES` context
    4227: .    its - iteration number
    4228: .    norm - 2-norm function value (may be estimated)
    4229: -    mctx - [optional] monitoring context

    4231:    Level: advanced

    4233: .seealso: [](ch_snes), `SNESMonitorSet()`
    4234: M*/

    4236: /*@C
    4237:   SNESMonitorSet - Sets an ADDITIONAL function that is to be used at every
    4238:   iteration of the `SNES` nonlinear solver to display the iteration's
    4239:   progress.

    4241:   Logically Collective

    4243:   Input Parameters:
    4244: + snes           - the `SNES` context
    4245: . f              - the monitor function,  for the calling sequence see `SNESMonitorFunction`
    4246: . mctx           - [optional] user-defined context for private data for the monitor routine (use `NULL` if no context is desired)
    4247: - monitordestroy - [optional] routine that frees monitor context (may be `NULL`), see `PetscCtxDestroyFn` for the calling sequence

    4249:   Options Database Keys:
    4250: + -snes_monitor               - sets `SNESMonitorDefault()`
    4251: . -snes_monitor draw::draw_lg - sets line graph monitor,
    4252: - -snes_monitor_cancel        - cancels all monitors that have been hardwired into a code by calls to `SNESMonitorSet()`, but does not cancel those set via
    4253:                                 the options database.

    4255:   Level: intermediate

    4257:   Note:
    4258:   Several different monitoring routines may be set by calling
    4259:   `SNESMonitorSet()` multiple times; all will be called in the
    4260:   order in which they were set.

    4262:   Fortran Note:
    4263:   Only a single monitor function can be set for each `SNES` object

    4265: .seealso: [](ch_snes), `SNES`, `SNESSolve()`, `SNESMonitorDefault()`, `SNESMonitorCancel()`, `SNESMonitorFunction`, `PetscCtxDestroyFn`
    4266: @*/
    4267: PetscErrorCode SNESMonitorSet(SNES snes, PetscErrorCode (*f)(SNES, PetscInt, PetscReal, void *), void *mctx, PetscCtxDestroyFn *monitordestroy)
    4268: {
    4269:   PetscFunctionBegin;
    4271:   for (PetscInt i = 0; i < snes->numbermonitors; i++) {
    4272:     PetscBool identical;

    4274:     PetscCall(PetscMonitorCompare((PetscErrorCode (*)(void))(PetscVoidFn *)f, mctx, monitordestroy, (PetscErrorCode (*)(void))(PetscVoidFn *)snes->monitor[i], snes->monitorcontext[i], snes->monitordestroy[i], &identical));
    4275:     if (identical) PetscFunctionReturn(PETSC_SUCCESS);
    4276:   }
    4277:   PetscCheck(snes->numbermonitors < MAXSNESMONITORS, PETSC_COMM_SELF, PETSC_ERR_ARG_OUTOFRANGE, "Too many monitors set");
    4278:   snes->monitor[snes->numbermonitors]          = f;
    4279:   snes->monitordestroy[snes->numbermonitors]   = monitordestroy;
    4280:   snes->monitorcontext[snes->numbermonitors++] = mctx;
    4281:   PetscFunctionReturn(PETSC_SUCCESS);
    4282: }

    4284: /*@
    4285:   SNESMonitorCancel - Clears all the monitor functions for a `SNES` object.

    4287:   Logically Collective

    4289:   Input Parameter:
    4290: . snes - the `SNES` context

    4292:   Options Database Key:
    4293: . -snes_monitor_cancel - cancels all monitors that have been hardwired
    4294:                          into a code by calls to `SNESMonitorSet()`, but does not cancel those
    4295:                          set via the options database

    4297:   Level: intermediate

    4299:   Note:
    4300:   There is no way to clear one specific monitor from a `SNES` object.

    4302: .seealso: [](ch_snes), `SNES`, `SNESMonitorDefault()`, `SNESMonitorSet()`
    4303: @*/
    4304: PetscErrorCode SNESMonitorCancel(SNES snes)
    4305: {
    4306:   PetscInt i;

    4308:   PetscFunctionBegin;
    4310:   for (i = 0; i < snes->numbermonitors; i++) {
    4311:     if (snes->monitordestroy[i]) PetscCall((*snes->monitordestroy[i])(&snes->monitorcontext[i]));
    4312:   }
    4313:   snes->numbermonitors = 0;
    4314:   PetscFunctionReturn(PETSC_SUCCESS);
    4315: }

    4317: /*MC
    4318:     SNESConvergenceTestFunction - functional form used for testing of convergence of nonlinear solver

    4320:      Synopsis:
    4321: #include <petscsnes.h>
    4322:      PetscErrorCode SNESConvergenceTest(SNES snes, PetscInt it, PetscReal xnorm, PetscReal gnorm, PetscReal f, SNESConvergedReason *reason, void *cctx)

    4324:      Collective

    4326:     Input Parameters:
    4327: +    snes - the `SNES` context
    4328: .    it - current iteration (0 is the first and is before any Newton step)
    4329: .    xnorm - 2-norm of current iterate
    4330: .    gnorm - 2-norm of current step
    4331: .    f - 2-norm of function
    4332: -    cctx - [optional] convergence context

    4334:     Output Parameter:
    4335: .    reason - reason for convergence/divergence, only needs to be set when convergence or divergence is detected

    4337:    Level: intermediate

    4339: .seealso: [](ch_snes), `SNES`, `SNESSolve`, `SNESSetConvergenceTest()`
    4340: M*/

    4342: /*@C
    4343:   SNESSetConvergenceTest - Sets the function that is to be used
    4344:   to test for convergence of the nonlinear iterative solution.

    4346:   Logically Collective

    4348:   Input Parameters:
    4349: + snes                        - the `SNES` context
    4350: . SNESConvergenceTestFunction - routine to test for convergence
    4351: . cctx                        - [optional] context for private data for the convergence routine  (may be `NULL`)
    4352: - destroy                     - [optional] destructor for the context (may be `NULL`; `PETSC_NULL_FUNCTION` in Fortran)

    4354:   Level: advanced

    4356: .seealso: [](ch_snes), `SNES`, `SNESConvergedDefault()`, `SNESConvergedSkip()`, `SNESConvergenceTestFunction`
    4357: @*/
    4358: PetscErrorCode SNESSetConvergenceTest(SNES snes, PetscErrorCode (*SNESConvergenceTestFunction)(SNES, PetscInt, PetscReal, PetscReal, PetscReal, SNESConvergedReason *, void *), void *cctx, PetscErrorCode (*destroy)(void *))
    4359: {
    4360:   PetscFunctionBegin;
    4362:   if (!SNESConvergenceTestFunction) SNESConvergenceTestFunction = SNESConvergedSkip;
    4363:   if (snes->ops->convergeddestroy) PetscCall((*snes->ops->convergeddestroy)(snes->cnvP));
    4364:   snes->ops->converged        = SNESConvergenceTestFunction;
    4365:   snes->ops->convergeddestroy = destroy;
    4366:   snes->cnvP                  = cctx;
    4367:   PetscFunctionReturn(PETSC_SUCCESS);
    4368: }

    4370: /*@
    4371:   SNESGetConvergedReason - Gets the reason the `SNES` iteration was stopped, which may be due to convergence, divergence, or stagnation

    4373:   Not Collective

    4375:   Input Parameter:
    4376: . snes - the `SNES` context

    4378:   Output Parameter:
    4379: . reason - negative value indicates diverged, positive value converged, see `SNESConvergedReason` for the individual convergence tests for complete lists

    4381:   Options Database Key:
    4382: . -snes_converged_reason - prints the reason to standard out

    4384:   Level: intermediate

    4386:   Note:
    4387:   Should only be called after the call the `SNESSolve()` is complete, if it is called earlier it returns the value `SNES__CONVERGED_ITERATING`.

    4389: .seealso: [](ch_snes), `SNESSolve()`, `SNESSetConvergenceTest()`, `SNESSetConvergedReason()`, `SNESConvergedReason`, `SNESGetConvergedReasonString()`
    4390: @*/
    4391: PetscErrorCode SNESGetConvergedReason(SNES snes, SNESConvergedReason *reason)
    4392: {
    4393:   PetscFunctionBegin;
    4395:   PetscAssertPointer(reason, 2);
    4396:   *reason = snes->reason;
    4397:   PetscFunctionReturn(PETSC_SUCCESS);
    4398: }

    4400: /*@C
    4401:   SNESGetConvergedReasonString - Return a human readable string for `SNESConvergedReason`

    4403:   Not Collective

    4405:   Input Parameter:
    4406: . snes - the `SNES` context

    4408:   Output Parameter:
    4409: . strreason - a human readable string that describes `SNES` converged reason

    4411:   Level: beginner

    4413: .seealso: [](ch_snes), `SNES`, `SNESGetConvergedReason()`
    4414: @*/
    4415: PetscErrorCode SNESGetConvergedReasonString(SNES snes, const char **strreason)
    4416: {
    4417:   PetscFunctionBegin;
    4419:   PetscAssertPointer(strreason, 2);
    4420:   *strreason = SNESConvergedReasons[snes->reason];
    4421:   PetscFunctionReturn(PETSC_SUCCESS);
    4422: }

    4424: /*@
    4425:   SNESSetConvergedReason - Sets the reason the `SNES` iteration was stopped.

    4427:   Not Collective

    4429:   Input Parameters:
    4430: + snes   - the `SNES` context
    4431: - reason - negative value indicates diverged, positive value converged, see `SNESConvergedReason` or the
    4432:             manual pages for the individual convergence tests for complete lists

    4434:   Level: developer

    4436:   Developer Note:
    4437:   Called inside the various `SNESSolve()` implementations

    4439: .seealso: [](ch_snes), `SNESGetConvergedReason()`, `SNESSetConvergenceTest()`, `SNESConvergedReason`
    4440: @*/
    4441: PetscErrorCode SNESSetConvergedReason(SNES snes, SNESConvergedReason reason)
    4442: {
    4443:   PetscFunctionBegin;
    4445:   PetscCheck(!snes->errorifnotconverged || reason > 0, PetscObjectComm((PetscObject)snes), PETSC_ERR_PLIB, "SNES code should have previously errored due to negative reason");
    4446:   snes->reason = reason;
    4447:   PetscFunctionReturn(PETSC_SUCCESS);
    4448: }

    4450: /*@
    4451:   SNESSetConvergenceHistory - Sets the arrays used to hold the convergence history.

    4453:   Logically Collective

    4455:   Input Parameters:
    4456: + snes  - iterative context obtained from `SNESCreate()`
    4457: . a     - array to hold history, this array will contain the function norms computed at each step
    4458: . its   - integer array holds the number of linear iterations for each solve.
    4459: . na    - size of `a` and `its`
    4460: - reset - `PETSC_TRUE` indicates each new nonlinear solve resets the history counter to zero,
    4461:           else it continues storing new values for new nonlinear solves after the old ones

    4463:   Level: intermediate

    4465:   Notes:
    4466:   If 'a' and 'its' are `NULL` then space is allocated for the history. If 'na' is `PETSC_DECIDE` (or, deprecated, `PETSC_DEFAULT`) then a
    4467:   default array of length 1,000 is allocated.

    4469:   This routine is useful, e.g., when running a code for purposes
    4470:   of accurate performance monitoring, when no I/O should be done
    4471:   during the section of code that is being timed.

    4473:   If the arrays run out of space after a number of iterations then the later values are not saved in the history

    4475: .seealso: [](ch_snes), `SNES`, `SNESSolve()`, `SNESGetConvergenceHistory()`
    4476: @*/
    4477: PetscErrorCode SNESSetConvergenceHistory(SNES snes, PetscReal a[], PetscInt its[], PetscInt na, PetscBool reset)
    4478: {
    4479:   PetscFunctionBegin;
    4481:   if (a) PetscAssertPointer(a, 2);
    4482:   if (its) PetscAssertPointer(its, 3);
    4483:   if (!a) {
    4484:     if (na == PETSC_DECIDE) na = 1000;
    4485:     PetscCall(PetscCalloc2(na, &a, na, &its));
    4486:     snes->conv_hist_alloc = PETSC_TRUE;
    4487:   }
    4488:   snes->conv_hist       = a;
    4489:   snes->conv_hist_its   = its;
    4490:   snes->conv_hist_max   = (size_t)na;
    4491:   snes->conv_hist_len   = 0;
    4492:   snes->conv_hist_reset = reset;
    4493:   PetscFunctionReturn(PETSC_SUCCESS);
    4494: }

    4496: #if defined(PETSC_HAVE_MATLAB)
    4497:   #include <engine.h> /* MATLAB include file */
    4498:   #include <mex.h>    /* MATLAB include file */

    4500: PETSC_EXTERN mxArray *SNESGetConvergenceHistoryMatlab(SNES snes)
    4501: {
    4502:   mxArray   *mat;
    4503:   PetscInt   i;
    4504:   PetscReal *ar;

    4506:   mat = mxCreateDoubleMatrix(snes->conv_hist_len, 1, mxREAL);
    4507:   ar  = (PetscReal *)mxGetData(mat);
    4508:   for (i = 0; i < snes->conv_hist_len; i++) ar[i] = snes->conv_hist[i];
    4509:   return mat;
    4510: }
    4511: #endif

    4513: /*@C
    4514:   SNESGetConvergenceHistory - Gets the arrays used to hold the convergence history.

    4516:   Not Collective

    4518:   Input Parameter:
    4519: . snes - iterative context obtained from `SNESCreate()`

    4521:   Output Parameters:
    4522: + a   - array to hold history, usually was set with `SNESSetConvergenceHistory()`
    4523: . its - integer array holds the number of linear iterations (or
    4524:          negative if not converged) for each solve.
    4525: - na  - size of `a` and `its`

    4527:   Level: intermediate

    4529:   Note:
    4530:   This routine is useful, e.g., when running a code for purposes
    4531:   of accurate performance monitoring, when no I/O should be done
    4532:   during the section of code that is being timed.

    4534:   Fortran Notes:
    4535:   Return the arrays with ``SNESRestoreConvergenceHistory()`

    4537:   Use the arguments
    4538: .vb
    4539:   PetscReal, pointer :: a(:)
    4540:   PetscInt, pointer :: its(:)
    4541: .ve

    4543: .seealso: [](ch_snes), `SNES`, `SNESSolve()`, `SNESSetConvergenceHistory()`
    4544: @*/
    4545: PetscErrorCode SNESGetConvergenceHistory(SNES snes, PetscReal *a[], PetscInt *its[], PetscInt *na)
    4546: {
    4547:   PetscFunctionBegin;
    4549:   if (a) *a = snes->conv_hist;
    4550:   if (its) *its = snes->conv_hist_its;
    4551:   if (na) *na = (PetscInt)snes->conv_hist_len;
    4552:   PetscFunctionReturn(PETSC_SUCCESS);
    4553: }

    4555: /*@C
    4556:   SNESSetUpdate - Sets the general-purpose update function called
    4557:   at the beginning of every iteration of the nonlinear solve. Specifically
    4558:   it is called just before the Jacobian is "evaluated" and after the function
    4559:   evaluation.

    4561:   Logically Collective

    4563:   Input Parameters:
    4564: + snes - The nonlinear solver context
    4565: - func - The update function; for calling sequence see `SNESUpdateFn`

    4567:   Level: advanced

    4569:   Notes:
    4570:   This is NOT what one uses to update the ghost points before a function evaluation, that should be done at the beginning of your function provided
    4571:   to `SNESSetFunction()`, or `SNESSetPicard()`
    4572:   This is not used by most users, and it is intended to provide a general hook that is run
    4573:   right before the direction step is computed.

    4575:   Users are free to modify the current residual vector,
    4576:   the current linearization point, or any other vector associated to the specific solver used.
    4577:   If such modifications take place, it is the user responsibility to update all the relevant
    4578:   vectors. For example, if one is adjusting the model parameters at each Newton step their code may look like
    4579: .vb
    4580:   PetscErrorCode update(SNES snes, PetscInt iteration)
    4581:   {
    4582:     PetscFunctionBeginUser;
    4583:     if (iteration > 0) {
    4584:       // update the model parameters here
    4585:       Vec x,f;
    4586:       PetscCall(SNESGetSolution(snes,&x));
    4587:       PetcCall(SNESGetFunction(snes,&f,NULL,NULL));
    4588:       PetscCall(SNESComputeFunction(snes,x,f));
    4589:     }
    4590:     PetscFunctionReturn(PETSC_SUCCESS);
    4591:   }
    4592: .ve

    4594:   There are a variety of function hooks one many set that are called at different stages of the nonlinear solution process, see the functions listed below.

    4596: .seealso: [](ch_snes), `SNES`, `SNESSolve()`, `SNESSetJacobian()`, `SNESLineSearchSetPreCheck()`, `SNESLineSearchSetPostCheck()`, `SNESNewtonTRSetPreCheck()`, `SNESNewtonTRSetPostCheck()`,
    4597:          `SNESMonitorSet()`
    4598: @*/
    4599: PetscErrorCode SNESSetUpdate(SNES snes, SNESUpdateFn *func)
    4600: {
    4601:   PetscFunctionBegin;
    4603:   snes->ops->update = func;
    4604:   PetscFunctionReturn(PETSC_SUCCESS);
    4605: }

    4607: /*@
    4608:   SNESConvergedReasonView - Displays the reason a `SNES` solve converged or diverged to a viewer

    4610:   Collective

    4612:   Input Parameters:
    4613: + snes   - iterative context obtained from `SNESCreate()`
    4614: - viewer - the viewer to display the reason

    4616:   Options Database Keys:
    4617: + -snes_converged_reason          - print reason for converged or diverged, also prints number of iterations
    4618: - -snes_converged_reason ::failed - only print reason and number of iterations when diverged

    4620:   Level: beginner

    4622:   Note:
    4623:   To change the format of the output call `PetscViewerPushFormat`(viewer,format) before this call. Use `PETSC_VIEWER_DEFAULT` for the default,
    4624:   use `PETSC_VIEWER_FAILED` to only display a reason if it fails.

    4626: .seealso: [](ch_snes), `SNESConvergedReason`, `PetscViewer`, `SNES`,
    4627:           `SNESCreate()`, `SNESSetUp()`, `SNESDestroy()`, `SNESSetTolerances()`, `SNESConvergedDefault()`, `SNESGetConvergedReason()`,
    4628:           `SNESConvergedReasonViewFromOptions()`,
    4629:           `PetscViewerPushFormat()`, `PetscViewerPopFormat()`
    4630: @*/
    4631: PetscErrorCode SNESConvergedReasonView(SNES snes, PetscViewer viewer)
    4632: {
    4633:   PetscViewerFormat format;
    4634:   PetscBool         isAscii;

    4636:   PetscFunctionBegin;
    4637:   if (!viewer) viewer = PETSC_VIEWER_STDOUT_(PetscObjectComm((PetscObject)snes));
    4638:   PetscCall(PetscObjectTypeCompare((PetscObject)viewer, PETSCVIEWERASCII, &isAscii));
    4639:   if (isAscii) {
    4640:     PetscCall(PetscViewerGetFormat(viewer, &format));
    4641:     PetscCall(PetscViewerASCIIAddTab(viewer, ((PetscObject)snes)->tablevel + 1));
    4642:     if (format == PETSC_VIEWER_ASCII_INFO_DETAIL) {
    4643:       DM       dm;
    4644:       Vec      u;
    4645:       PetscDS  prob;
    4646:       PetscInt Nf, f;
    4647:       PetscErrorCode (**exactSol)(PetscInt, PetscReal, const PetscReal[], PetscInt, PetscScalar[], void *);
    4648:       void    **exactCtx;
    4649:       PetscReal error;

    4651:       PetscCall(SNESGetDM(snes, &dm));
    4652:       PetscCall(SNESGetSolution(snes, &u));
    4653:       PetscCall(DMGetDS(dm, &prob));
    4654:       PetscCall(PetscDSGetNumFields(prob, &Nf));
    4655:       PetscCall(PetscMalloc2(Nf, &exactSol, Nf, &exactCtx));
    4656:       for (f = 0; f < Nf; ++f) PetscCall(PetscDSGetExactSolution(prob, f, &exactSol[f], &exactCtx[f]));
    4657:       PetscCall(DMComputeL2Diff(dm, 0.0, exactSol, exactCtx, u, &error));
    4658:       PetscCall(PetscFree2(exactSol, exactCtx));
    4659:       if (error < 1.0e-11) PetscCall(PetscViewerASCIIPrintf(viewer, "L_2 Error: < 1.0e-11\n"));
    4660:       else PetscCall(PetscViewerASCIIPrintf(viewer, "L_2 Error: %g\n", (double)error));
    4661:     }
    4662:     if (snes->reason > 0 && format != PETSC_VIEWER_FAILED) {
    4663:       if (((PetscObject)snes)->prefix) {
    4664:         PetscCall(PetscViewerASCIIPrintf(viewer, "Nonlinear %s solve converged due to %s iterations %" PetscInt_FMT "\n", ((PetscObject)snes)->prefix, SNESConvergedReasons[snes->reason], snes->iter));
    4665:       } else {
    4666:         PetscCall(PetscViewerASCIIPrintf(viewer, "Nonlinear solve converged due to %s iterations %" PetscInt_FMT "\n", SNESConvergedReasons[snes->reason], snes->iter));
    4667:       }
    4668:     } else if (snes->reason <= 0) {
    4669:       if (((PetscObject)snes)->prefix) {
    4670:         PetscCall(PetscViewerASCIIPrintf(viewer, "Nonlinear %s solve did not converge due to %s iterations %" PetscInt_FMT "\n", ((PetscObject)snes)->prefix, SNESConvergedReasons[snes->reason], snes->iter));
    4671:       } else {
    4672:         PetscCall(PetscViewerASCIIPrintf(viewer, "Nonlinear solve did not converge due to %s iterations %" PetscInt_FMT "\n", SNESConvergedReasons[snes->reason], snes->iter));
    4673:       }
    4674:     }
    4675:     PetscCall(PetscViewerASCIISubtractTab(viewer, ((PetscObject)snes)->tablevel + 1));
    4676:   }
    4677:   PetscFunctionReturn(PETSC_SUCCESS);
    4678: }

    4680: /*@C
    4681:   SNESConvergedReasonViewSet - Sets an ADDITIONAL function that is to be used at the
    4682:   end of the nonlinear solver to display the convergence reason of the nonlinear solver.

    4684:   Logically Collective

    4686:   Input Parameters:
    4687: + snes              - the `SNES` context
    4688: . f                 - the `SNESConvergedReason` view function
    4689: . vctx              - [optional] user-defined context for private data for the `SNESConvergedReason` view function (use `NULL` if no context is desired)
    4690: - reasonviewdestroy - [optional] routine that frees the context (may be `NULL`), see `PetscCtxDestroyFn` for the calling sequence

    4692:   Calling sequence of `f`:
    4693: + snes - the `SNES` context
    4694: - vctx - [optional] context for private data for the function

    4696:   Options Database Keys:
    4697: + -snes_converged_reason             - sets a default `SNESConvergedReasonView()`
    4698: - -snes_converged_reason_view_cancel - cancels all converged reason viewers that have been hardwired into a code by
    4699:                                        calls to `SNESConvergedReasonViewSet()`, but does not cancel those set via the options database.

    4701:   Level: intermediate

    4703:   Note:
    4704:   Several different converged reason view routines may be set by calling
    4705:   `SNESConvergedReasonViewSet()` multiple times; all will be called in the
    4706:   order in which they were set.

    4708: .seealso: [](ch_snes), `SNES`, `SNESSolve()`, `SNESConvergedReason`, `SNESGetConvergedReason()`, `SNESConvergedReasonView()`, `SNESConvergedReasonViewCancel()`,
    4709:           `PetscCtxDestroyFn`
    4710: @*/
    4711: PetscErrorCode SNESConvergedReasonViewSet(SNES snes, PetscErrorCode (*f)(SNES snes, void *vctx), void *vctx, PetscCtxDestroyFn *reasonviewdestroy)
    4712: {
    4713:   PetscFunctionBegin;
    4715:   for (PetscInt i = 0; i < snes->numberreasonviews; i++) {
    4716:     PetscBool identical;

    4718:     PetscCall(PetscMonitorCompare((PetscErrorCode (*)(void))(PetscVoidFn *)f, vctx, reasonviewdestroy, (PetscErrorCode (*)(void))(PetscVoidFn *)snes->reasonview[i], snes->reasonviewcontext[i], snes->reasonviewdestroy[i], &identical));
    4719:     if (identical) PetscFunctionReturn(PETSC_SUCCESS);
    4720:   }
    4721:   PetscCheck(snes->numberreasonviews < MAXSNESREASONVIEWS, PETSC_COMM_SELF, PETSC_ERR_ARG_OUTOFRANGE, "Too many SNES reasonview set");
    4722:   snes->reasonview[snes->numberreasonviews]          = f;
    4723:   snes->reasonviewdestroy[snes->numberreasonviews]   = reasonviewdestroy;
    4724:   snes->reasonviewcontext[snes->numberreasonviews++] = vctx;
    4725:   PetscFunctionReturn(PETSC_SUCCESS);
    4726: }

    4728: /*@
    4729:   SNESConvergedReasonViewFromOptions - Processes command line options to determine if/how a `SNESConvergedReason` is to be viewed at the end of `SNESSolve()`
    4730:   All the user-provided viewer routines set with `SNESConvergedReasonViewSet()` will be called, if they exist.

    4732:   Collective

    4734:   Input Parameter:
    4735: . snes - the `SNES` object

    4737:   Level: advanced

    4739: .seealso: [](ch_snes), `SNES`, `SNESConvergedReason`, `SNESConvergedReasonViewSet()`, `SNESCreate()`, `SNESSetUp()`, `SNESDestroy()`,
    4740:           `SNESSetTolerances()`, `SNESConvergedDefault()`, `SNESGetConvergedReason()`, `SNESConvergedReasonView()`
    4741: @*/
    4742: PetscErrorCode SNESConvergedReasonViewFromOptions(SNES snes)
    4743: {
    4744:   static PetscBool incall = PETSC_FALSE;

    4746:   PetscFunctionBegin;
    4747:   if (incall) PetscFunctionReturn(PETSC_SUCCESS);
    4748:   incall = PETSC_TRUE;

    4750:   /* All user-provided viewers are called first, if they exist. */
    4751:   for (PetscInt i = 0; i < snes->numberreasonviews; i++) PetscCall((*snes->reasonview[i])(snes, snes->reasonviewcontext[i]));

    4753:   /* Call PETSc default routine if users ask for it */
    4754:   if (snes->convergedreasonviewer) {
    4755:     PetscCall(PetscViewerPushFormat(snes->convergedreasonviewer, snes->convergedreasonformat));
    4756:     PetscCall(SNESConvergedReasonView(snes, snes->convergedreasonviewer));
    4757:     PetscCall(PetscViewerPopFormat(snes->convergedreasonviewer));
    4758:   }
    4759:   incall = PETSC_FALSE;
    4760:   PetscFunctionReturn(PETSC_SUCCESS);
    4761: }

    4763: /*@
    4764:   SNESSolve - Solves a nonlinear system $F(x) = b $ associated with a `SNES` object

    4766:   Collective

    4768:   Input Parameters:
    4769: + snes - the `SNES` context
    4770: . b    - the constant part of the equation $F(x) = b$, or `NULL` to use zero.
    4771: - x    - the solution vector.

    4773:   Level: beginner

    4775:   Note:
    4776:   The user should initialize the vector, `x`, with the initial guess
    4777:   for the nonlinear solve prior to calling `SNESSolve()` .

    4779: .seealso: [](ch_snes), `SNES`, `SNESCreate()`, `SNESDestroy()`, `SNESSetFunction()`, `SNESSetJacobian()`, `SNESSetGridSequence()`, `SNESGetSolution()`,
    4780:           `SNESNewtonTRSetPreCheck()`, `SNESNewtonTRGetPreCheck()`, `SNESNewtonTRSetPostCheck()`, `SNESNewtonTRGetPostCheck()`,
    4781:           `SNESLineSearchSetPostCheck()`, `SNESLineSearchGetPostCheck()`, `SNESLineSearchSetPreCheck()`, `SNESLineSearchGetPreCheck()`
    4782: @*/
    4783: PetscErrorCode SNESSolve(SNES snes, Vec b, Vec x)
    4784: {
    4785:   PetscBool flg;
    4786:   PetscInt  grid;
    4787:   Vec       xcreated = NULL;
    4788:   DM        dm;

    4790:   PetscFunctionBegin;
    4793:   if (x) PetscCheckSameComm(snes, 1, x, 3);
    4795:   if (b) PetscCheckSameComm(snes, 1, b, 2);

    4797:   /* High level operations using the nonlinear solver */
    4798:   {
    4799:     PetscViewer       viewer;
    4800:     PetscViewerFormat format;
    4801:     PetscInt          num;
    4802:     PetscBool         flg;
    4803:     static PetscBool  incall = PETSC_FALSE;

    4805:     if (!incall) {
    4806:       /* Estimate the convergence rate of the discretization */
    4807:       PetscCall(PetscOptionsCreateViewer(PetscObjectComm((PetscObject)snes), ((PetscObject)snes)->options, ((PetscObject)snes)->prefix, "-snes_convergence_estimate", &viewer, &format, &flg));
    4808:       if (flg) {
    4809:         PetscConvEst conv;
    4810:         DM           dm;
    4811:         PetscReal   *alpha; /* Convergence rate of the solution error for each field in the L_2 norm */
    4812:         PetscInt     Nf;

    4814:         incall = PETSC_TRUE;
    4815:         PetscCall(SNESGetDM(snes, &dm));
    4816:         PetscCall(DMGetNumFields(dm, &Nf));
    4817:         PetscCall(PetscCalloc1(Nf, &alpha));
    4818:         PetscCall(PetscConvEstCreate(PetscObjectComm((PetscObject)snes), &conv));
    4819:         PetscCall(PetscConvEstSetSolver(conv, (PetscObject)snes));
    4820:         PetscCall(PetscConvEstSetFromOptions(conv));
    4821:         PetscCall(PetscConvEstSetUp(conv));
    4822:         PetscCall(PetscConvEstGetConvRate(conv, alpha));
    4823:         PetscCall(PetscViewerPushFormat(viewer, format));
    4824:         PetscCall(PetscConvEstRateView(conv, alpha, viewer));
    4825:         PetscCall(PetscViewerPopFormat(viewer));
    4826:         PetscCall(PetscViewerDestroy(&viewer));
    4827:         PetscCall(PetscConvEstDestroy(&conv));
    4828:         PetscCall(PetscFree(alpha));
    4829:         incall = PETSC_FALSE;
    4830:       }
    4831:       /* Adaptively refine the initial grid */
    4832:       num = 1;
    4833:       PetscCall(PetscOptionsGetInt(NULL, ((PetscObject)snes)->prefix, "-snes_adapt_initial", &num, &flg));
    4834:       if (flg) {
    4835:         DMAdaptor adaptor;

    4837:         incall = PETSC_TRUE;
    4838:         PetscCall(DMAdaptorCreate(PetscObjectComm((PetscObject)snes), &adaptor));
    4839:         PetscCall(DMAdaptorSetSolver(adaptor, snes));
    4840:         PetscCall(DMAdaptorSetSequenceLength(adaptor, num));
    4841:         PetscCall(DMAdaptorSetFromOptions(adaptor));
    4842:         PetscCall(DMAdaptorSetUp(adaptor));
    4843:         PetscCall(DMAdaptorAdapt(adaptor, x, DM_ADAPTATION_INITIAL, &dm, &x));
    4844:         PetscCall(DMAdaptorDestroy(&adaptor));
    4845:         incall = PETSC_FALSE;
    4846:       }
    4847:       /* Use grid sequencing to adapt */
    4848:       num = 0;
    4849:       PetscCall(PetscOptionsGetInt(NULL, ((PetscObject)snes)->prefix, "-snes_adapt_sequence", &num, NULL));
    4850:       if (num) {
    4851:         DMAdaptor   adaptor;
    4852:         const char *prefix;

    4854:         incall = PETSC_TRUE;
    4855:         PetscCall(DMAdaptorCreate(PetscObjectComm((PetscObject)snes), &adaptor));
    4856:         PetscCall(SNESGetOptionsPrefix(snes, &prefix));
    4857:         PetscCall(DMAdaptorSetOptionsPrefix(adaptor, prefix));
    4858:         PetscCall(DMAdaptorSetSolver(adaptor, snes));
    4859:         PetscCall(DMAdaptorSetSequenceLength(adaptor, num));
    4860:         PetscCall(DMAdaptorSetFromOptions(adaptor));
    4861:         PetscCall(DMAdaptorSetUp(adaptor));
    4862:         PetscCall(PetscObjectViewFromOptions((PetscObject)adaptor, NULL, "-snes_adapt_view"));
    4863:         PetscCall(DMAdaptorAdapt(adaptor, x, DM_ADAPTATION_SEQUENTIAL, &dm, &x));
    4864:         PetscCall(DMAdaptorDestroy(&adaptor));
    4865:         incall = PETSC_FALSE;
    4866:       }
    4867:     }
    4868:   }
    4869:   if (!x) x = snes->vec_sol;
    4870:   if (!x) {
    4871:     PetscCall(SNESGetDM(snes, &dm));
    4872:     PetscCall(DMCreateGlobalVector(dm, &xcreated));
    4873:     x = xcreated;
    4874:   }
    4875:   PetscCall(SNESViewFromOptions(snes, NULL, "-snes_view_pre"));

    4877:   for (grid = 0; grid < snes->gridsequence; grid++) PetscCall(PetscViewerASCIIPushTab(PETSC_VIEWER_STDOUT_(PetscObjectComm((PetscObject)snes))));
    4878:   for (grid = 0; grid < snes->gridsequence + 1; grid++) {
    4879:     /* set solution vector */
    4880:     if (!grid) PetscCall(PetscObjectReference((PetscObject)x));
    4881:     PetscCall(VecDestroy(&snes->vec_sol));
    4882:     snes->vec_sol = x;
    4883:     PetscCall(SNESGetDM(snes, &dm));

    4885:     /* set affine vector if provided */
    4886:     if (b) PetscCall(PetscObjectReference((PetscObject)b));
    4887:     PetscCall(VecDestroy(&snes->vec_rhs));
    4888:     snes->vec_rhs = b;

    4890:     if (snes->vec_rhs) PetscCheck(snes->vec_func != snes->vec_rhs, PETSC_COMM_SELF, PETSC_ERR_ARG_IDN, "Right hand side vector cannot be function vector");
    4891:     PetscCheck(snes->vec_func != snes->vec_sol, PETSC_COMM_SELF, PETSC_ERR_ARG_IDN, "Solution vector cannot be function vector");
    4892:     PetscCheck(snes->vec_rhs != snes->vec_sol, PETSC_COMM_SELF, PETSC_ERR_ARG_IDN, "Solution vector cannot be right-hand side vector");
    4893:     if (!snes->vec_sol_update /* && snes->vec_sol */) PetscCall(VecDuplicate(snes->vec_sol, &snes->vec_sol_update));
    4894:     PetscCall(DMShellSetGlobalVector(dm, snes->vec_sol));
    4895:     PetscCall(SNESSetUp(snes));

    4897:     if (!grid) {
    4898:       if (snes->ops->computeinitialguess) PetscCallBack("SNES callback compute initial guess", (*snes->ops->computeinitialguess)(snes, snes->vec_sol, snes->initialguessP));
    4899:     }

    4901:     if (snes->conv_hist_reset) snes->conv_hist_len = 0;
    4902:     PetscCall(SNESResetCounters(snes));
    4903:     snes->reason = SNES_CONVERGED_ITERATING;
    4904:     PetscCall(PetscLogEventBegin(SNES_Solve, snes, 0, 0, 0));
    4905:     PetscUseTypeMethod(snes, solve);
    4906:     PetscCall(PetscLogEventEnd(SNES_Solve, snes, 0, 0, 0));
    4907:     PetscCheck(snes->reason, PETSC_COMM_SELF, PETSC_ERR_PLIB, "Internal error, solver %s returned without setting converged reason", ((PetscObject)snes)->type_name);
    4908:     snes->domainerror = PETSC_FALSE; /* clear the flag if it has been set */

    4910:     if (snes->lagjac_persist) snes->jac_iter += snes->iter;
    4911:     if (snes->lagpre_persist) snes->pre_iter += snes->iter;

    4913:     PetscCall(PetscOptionsCreateViewer(PetscObjectComm((PetscObject)snes), ((PetscObject)snes)->options, ((PetscObject)snes)->prefix, "-snes_test_local_min", NULL, NULL, &flg));
    4914:     if (flg && !PetscPreLoadingOn) PetscCall(SNESTestLocalMin(snes));
    4915:     /* Call converged reason views. This may involve user-provided viewers as well */
    4916:     PetscCall(SNESConvergedReasonViewFromOptions(snes));

    4918:     if (snes->errorifnotconverged) {
    4919:       if (snes->reason < 0) PetscCall(SNESMonitorCancel(snes));
    4920:       PetscCheck(snes->reason >= 0, PetscObjectComm((PetscObject)snes), PETSC_ERR_NOT_CONVERGED, "SNESSolve has not converged");
    4921:     }
    4922:     if (snes->reason < 0) break;
    4923:     if (grid < snes->gridsequence) {
    4924:       DM  fine;
    4925:       Vec xnew;
    4926:       Mat interp;

    4928:       PetscCall(DMRefine(snes->dm, PetscObjectComm((PetscObject)snes), &fine));
    4929:       PetscCheck(fine, PetscObjectComm((PetscObject)snes), PETSC_ERR_ARG_INCOMP, "DMRefine() did not perform any refinement, cannot continue grid sequencing");
    4930:       PetscCall(DMGetCoordinatesLocalSetUp(fine));
    4931:       PetscCall(DMCreateInterpolation(snes->dm, fine, &interp, NULL));
    4932:       PetscCall(DMCreateGlobalVector(fine, &xnew));
    4933:       PetscCall(MatInterpolate(interp, x, xnew));
    4934:       PetscCall(DMInterpolate(snes->dm, interp, fine));
    4935:       PetscCall(MatDestroy(&interp));
    4936:       x = xnew;

    4938:       PetscCall(SNESReset(snes));
    4939:       PetscCall(SNESSetDM(snes, fine));
    4940:       PetscCall(SNESResetFromOptions(snes));
    4941:       PetscCall(DMDestroy(&fine));
    4942:       PetscCall(PetscViewerASCIIPopTab(PETSC_VIEWER_STDOUT_(PetscObjectComm((PetscObject)snes))));
    4943:     }
    4944:   }
    4945:   PetscCall(SNESViewFromOptions(snes, NULL, "-snes_view"));
    4946:   PetscCall(VecViewFromOptions(snes->vec_sol, (PetscObject)snes, "-snes_view_solution"));
    4947:   PetscCall(DMMonitor(snes->dm));
    4948:   PetscCall(SNESMonitorPauseFinal_Internal(snes));

    4950:   PetscCall(VecDestroy(&xcreated));
    4951:   PetscCall(PetscObjectSAWsBlock((PetscObject)snes));
    4952:   PetscFunctionReturn(PETSC_SUCCESS);
    4953: }

    4955: /* --------- Internal routines for SNES Package --------- */

    4957: /*@
    4958:   SNESSetType - Sets the algorithm/method to be used to solve the nonlinear system with the given `SNES`

    4960:   Collective

    4962:   Input Parameters:
    4963: + snes - the `SNES` context
    4964: - type - a known method

    4966:   Options Database Key:
    4967: . -snes_type <type> - Sets the method; use -help for a list
    4968:    of available methods (for instance, newtonls or newtontr)

    4970:   Level: intermediate

    4972:   Notes:
    4973:   See `SNESType` for available methods (for instance)
    4974: +    `SNESNEWTONLS` - Newton's method with line search
    4975:   (systems of nonlinear equations)
    4976: -    `SNESNEWTONTR` - Newton's method with trust region
    4977:   (systems of nonlinear equations)

    4979:   Normally, it is best to use the `SNESSetFromOptions()` command and then
    4980:   set the `SNES` solver type from the options database rather than by using
    4981:   this routine.  Using the options database provides the user with
    4982:   maximum flexibility in evaluating the many nonlinear solvers.
    4983:   The `SNESSetType()` routine is provided for those situations where it
    4984:   is necessary to set the nonlinear solver independently of the command
    4985:   line or options database.  This might be the case, for example, when
    4986:   the choice of solver changes during the execution of the program,
    4987:   and the user's application is taking responsibility for choosing the
    4988:   appropriate method.

    4990:   Developer Note:
    4991:   `SNESRegister()` adds a constructor for a new `SNESType` to `SNESList`, `SNESSetType()` locates
    4992:   the constructor in that list and calls it to create the specific object.

    4994: .seealso: [](ch_snes), `SNES`, `SNESSolve()`, `SNESType`, `SNESCreate()`, `SNESDestroy()`, `SNESGetType()`, `SNESSetFromOptions()`
    4995: @*/
    4996: PetscErrorCode SNESSetType(SNES snes, SNESType type)
    4997: {
    4998:   PetscBool match;
    4999:   PetscErrorCode (*r)(SNES);

    5001:   PetscFunctionBegin;
    5003:   PetscAssertPointer(type, 2);

    5005:   PetscCall(PetscObjectTypeCompare((PetscObject)snes, type, &match));
    5006:   if (match) PetscFunctionReturn(PETSC_SUCCESS);

    5008:   PetscCall(PetscFunctionListFind(SNESList, type, &r));
    5009:   PetscCheck(r, PetscObjectComm((PetscObject)snes), PETSC_ERR_ARG_UNKNOWN_TYPE, "Unable to find requested SNES type %s", type);
    5010:   /* Destroy the previous private SNES context */
    5011:   PetscTryTypeMethod(snes, destroy);
    5012:   /* Reinitialize type-specific function pointers in SNESOps structure */
    5013:   snes->ops->reset          = NULL;
    5014:   snes->ops->setup          = NULL;
    5015:   snes->ops->solve          = NULL;
    5016:   snes->ops->view           = NULL;
    5017:   snes->ops->setfromoptions = NULL;
    5018:   snes->ops->destroy        = NULL;

    5020:   /* It may happen the user has customized the line search before calling SNESSetType */
    5021:   if (((PetscObject)snes)->type_name) PetscCall(SNESLineSearchDestroy(&snes->linesearch));

    5023:   /* Call the SNESCreate_XXX routine for this particular Nonlinear solver */
    5024:   snes->setupcalled = PETSC_FALSE;

    5026:   PetscCall(PetscObjectChangeTypeName((PetscObject)snes, type));
    5027:   PetscCall((*r)(snes));
    5028:   PetscFunctionReturn(PETSC_SUCCESS);
    5029: }

    5031: /*@
    5032:   SNESGetType - Gets the `SNES` method type and name (as a string).

    5034:   Not Collective

    5036:   Input Parameter:
    5037: . snes - nonlinear solver context

    5039:   Output Parameter:
    5040: . type - `SNES` method (a character string)

    5042:   Level: intermediate

    5044: .seealso: [](ch_snes), `SNESSetType()`, `SNESType`, `SNESSetFromOptions()`, `SNES`
    5045: @*/
    5046: PetscErrorCode SNESGetType(SNES snes, SNESType *type)
    5047: {
    5048:   PetscFunctionBegin;
    5050:   PetscAssertPointer(type, 2);
    5051:   *type = ((PetscObject)snes)->type_name;
    5052:   PetscFunctionReturn(PETSC_SUCCESS);
    5053: }

    5055: /*@
    5056:   SNESSetSolution - Sets the solution vector for use by the `SNES` routines.

    5058:   Logically Collective

    5060:   Input Parameters:
    5061: + snes - the `SNES` context obtained from `SNESCreate()`
    5062: - u    - the solution vector

    5064:   Level: beginner

    5066: .seealso: [](ch_snes), `SNES`, `SNESSolve()`, `SNESGetSolution()`, `Vec`
    5067: @*/
    5068: PetscErrorCode SNESSetSolution(SNES snes, Vec u)
    5069: {
    5070:   DM dm;

    5072:   PetscFunctionBegin;
    5075:   PetscCall(PetscObjectReference((PetscObject)u));
    5076:   PetscCall(VecDestroy(&snes->vec_sol));

    5078:   snes->vec_sol = u;

    5080:   PetscCall(SNESGetDM(snes, &dm));
    5081:   PetscCall(DMShellSetGlobalVector(dm, u));
    5082:   PetscFunctionReturn(PETSC_SUCCESS);
    5083: }

    5085: /*@
    5086:   SNESGetSolution - Returns the vector where the approximate solution is
    5087:   stored. This is the fine grid solution when using `SNESSetGridSequence()`.

    5089:   Not Collective, but `x` is parallel if `snes` is parallel

    5091:   Input Parameter:
    5092: . snes - the `SNES` context

    5094:   Output Parameter:
    5095: . x - the solution

    5097:   Level: intermediate

    5099: .seealso: [](ch_snes), `SNESSetSolution()`, `SNESSolve()`, `SNES`, `SNESGetSolutionUpdate()`, `SNESGetFunction()`
    5100: @*/
    5101: PetscErrorCode SNESGetSolution(SNES snes, Vec *x)
    5102: {
    5103:   PetscFunctionBegin;
    5105:   PetscAssertPointer(x, 2);
    5106:   *x = snes->vec_sol;
    5107:   PetscFunctionReturn(PETSC_SUCCESS);
    5108: }

    5110: /*@
    5111:   SNESGetSolutionUpdate - Returns the vector where the solution update is
    5112:   stored.

    5114:   Not Collective, but `x` is parallel if `snes` is parallel

    5116:   Input Parameter:
    5117: . snes - the `SNES` context

    5119:   Output Parameter:
    5120: . x - the solution update

    5122:   Level: advanced

    5124: .seealso: [](ch_snes), `SNES`, `SNESGetSolution()`, `SNESGetFunction()`
    5125: @*/
    5126: PetscErrorCode SNESGetSolutionUpdate(SNES snes, Vec *x)
    5127: {
    5128:   PetscFunctionBegin;
    5130:   PetscAssertPointer(x, 2);
    5131:   *x = snes->vec_sol_update;
    5132:   PetscFunctionReturn(PETSC_SUCCESS);
    5133: }

    5135: /*@C
    5136:   SNESGetFunction - Returns the function that defines the nonlinear system set with `SNESSetFunction()`

    5138:   Not Collective, but `r` is parallel if `snes` is parallel. Collective if `r` is requested, but has not been created yet.

    5140:   Input Parameter:
    5141: . snes - the `SNES` context

    5143:   Output Parameters:
    5144: + r   - the vector that is used to store residuals (or `NULL` if you don't want it)
    5145: . f   - the function (or `NULL` if you don't want it);  for calling sequence see `SNESFunctionFn`
    5146: - ctx - the function context (or `NULL` if you don't want it)

    5148:   Level: advanced

    5150:   Note:
    5151:   The vector `r` DOES NOT, in general, contain the current value of the `SNES` nonlinear function

    5153: .seealso: [](ch_snes), `SNES`, `SNESSolve()`, `SNESSetFunction()`, `SNESGetSolution()`, `SNESFunctionFn`
    5154: @*/
    5155: PetscErrorCode SNESGetFunction(SNES snes, Vec *r, SNESFunctionFn **f, void **ctx)
    5156: {
    5157:   DM dm;

    5159:   PetscFunctionBegin;
    5161:   if (r) {
    5162:     if (!snes->vec_func) {
    5163:       if (snes->vec_rhs) {
    5164:         PetscCall(VecDuplicate(snes->vec_rhs, &snes->vec_func));
    5165:       } else if (snes->vec_sol) {
    5166:         PetscCall(VecDuplicate(snes->vec_sol, &snes->vec_func));
    5167:       } else if (snes->dm) {
    5168:         PetscCall(DMCreateGlobalVector(snes->dm, &snes->vec_func));
    5169:       }
    5170:     }
    5171:     *r = snes->vec_func;
    5172:   }
    5173:   PetscCall(SNESGetDM(snes, &dm));
    5174:   PetscCall(DMSNESGetFunction(dm, f, ctx));
    5175:   PetscFunctionReturn(PETSC_SUCCESS);
    5176: }

    5178: /*@C
    5179:   SNESGetNGS - Returns the function and context set with `SNESSetNGS()`

    5181:   Input Parameter:
    5182: . snes - the `SNES` context

    5184:   Output Parameters:
    5185: + f   - the function (or `NULL`) see `SNESNGSFn` for calling sequence
    5186: - ctx - the function context (or `NULL`)

    5188:   Level: advanced

    5190: .seealso: [](ch_snes), `SNESSetNGS()`, `SNESGetFunction()`, `SNESNGSFn`
    5191: @*/
    5192: PetscErrorCode SNESGetNGS(SNES snes, SNESNGSFn **f, void **ctx)
    5193: {
    5194:   DM dm;

    5196:   PetscFunctionBegin;
    5198:   PetscCall(SNESGetDM(snes, &dm));
    5199:   PetscCall(DMSNESGetNGS(dm, f, ctx));
    5200:   PetscFunctionReturn(PETSC_SUCCESS);
    5201: }

    5203: /*@
    5204:   SNESSetOptionsPrefix - Sets the prefix used for searching for all
    5205:   `SNES` options in the database.

    5207:   Logically Collective

    5209:   Input Parameters:
    5210: + snes   - the `SNES` context
    5211: - prefix - the prefix to prepend to all option names

    5213:   Level: advanced

    5215:   Note:
    5216:   A hyphen (-) must NOT be given at the beginning of the prefix name.
    5217:   The first character of all runtime options is AUTOMATICALLY the hyphen.

    5219: .seealso: [](ch_snes), `SNES`, `SNESSetFromOptions()`, `SNESAppendOptionsPrefix()`
    5220: @*/
    5221: PetscErrorCode SNESSetOptionsPrefix(SNES snes, const char prefix[])
    5222: {
    5223:   PetscFunctionBegin;
    5225:   PetscCall(PetscObjectSetOptionsPrefix((PetscObject)snes, prefix));
    5226:   if (!snes->ksp) PetscCall(SNESGetKSP(snes, &snes->ksp));
    5227:   if (snes->linesearch) {
    5228:     PetscCall(SNESGetLineSearch(snes, &snes->linesearch));
    5229:     PetscCall(PetscObjectSetOptionsPrefix((PetscObject)snes->linesearch, prefix));
    5230:   }
    5231:   PetscCall(KSPSetOptionsPrefix(snes->ksp, prefix));
    5232:   PetscFunctionReturn(PETSC_SUCCESS);
    5233: }

    5235: /*@
    5236:   SNESAppendOptionsPrefix - Appends to the prefix used for searching for all
    5237:   `SNES` options in the database.

    5239:   Logically Collective

    5241:   Input Parameters:
    5242: + snes   - the `SNES` context
    5243: - prefix - the prefix to prepend to all option names

    5245:   Level: advanced

    5247:   Note:
    5248:   A hyphen (-) must NOT be given at the beginning of the prefix name.
    5249:   The first character of all runtime options is AUTOMATICALLY the hyphen.

    5251: .seealso: [](ch_snes), `SNESGetOptionsPrefix()`, `SNESSetOptionsPrefix()`
    5252: @*/
    5253: PetscErrorCode SNESAppendOptionsPrefix(SNES snes, const char prefix[])
    5254: {
    5255:   PetscFunctionBegin;
    5257:   PetscCall(PetscObjectAppendOptionsPrefix((PetscObject)snes, prefix));
    5258:   if (!snes->ksp) PetscCall(SNESGetKSP(snes, &snes->ksp));
    5259:   if (snes->linesearch) {
    5260:     PetscCall(SNESGetLineSearch(snes, &snes->linesearch));
    5261:     PetscCall(PetscObjectAppendOptionsPrefix((PetscObject)snes->linesearch, prefix));
    5262:   }
    5263:   PetscCall(KSPAppendOptionsPrefix(snes->ksp, prefix));
    5264:   PetscFunctionReturn(PETSC_SUCCESS);
    5265: }

    5267: /*@
    5268:   SNESGetOptionsPrefix - Gets the prefix used for searching for all
    5269:   `SNES` options in the database.

    5271:   Not Collective

    5273:   Input Parameter:
    5274: . snes - the `SNES` context

    5276:   Output Parameter:
    5277: . prefix - pointer to the prefix string used

    5279:   Level: advanced

    5281: .seealso: [](ch_snes), `SNES`, `SNESSetOptionsPrefix()`, `SNESAppendOptionsPrefix()`
    5282: @*/
    5283: PetscErrorCode SNESGetOptionsPrefix(SNES snes, const char *prefix[])
    5284: {
    5285:   PetscFunctionBegin;
    5287:   PetscCall(PetscObjectGetOptionsPrefix((PetscObject)snes, prefix));
    5288:   PetscFunctionReturn(PETSC_SUCCESS);
    5289: }

    5291: /*@C
    5292:   SNESRegister - Adds a method to the nonlinear solver package.

    5294:   Not Collective

    5296:   Input Parameters:
    5297: + sname    - name of a new user-defined solver
    5298: - function - routine to create method context

    5300:   Level: advanced

    5302:   Note:
    5303:   `SNESRegister()` may be called multiple times to add several user-defined solvers.

    5305:   Example Usage:
    5306: .vb
    5307:    SNESRegister("my_solver", MySolverCreate);
    5308: .ve

    5310:   Then, your solver can be chosen with the procedural interface via
    5311: .vb
    5312:   SNESSetType(snes, "my_solver")
    5313: .ve
    5314:   or at runtime via the option
    5315: .vb
    5316:   -snes_type my_solver
    5317: .ve

    5319: .seealso: [](ch_snes), `SNESRegisterAll()`, `SNESRegisterDestroy()`
    5320: @*/
    5321: PetscErrorCode SNESRegister(const char sname[], PetscErrorCode (*function)(SNES))
    5322: {
    5323:   PetscFunctionBegin;
    5324:   PetscCall(SNESInitializePackage());
    5325:   PetscCall(PetscFunctionListAdd(&SNESList, sname, function));
    5326:   PetscFunctionReturn(PETSC_SUCCESS);
    5327: }

    5329: PetscErrorCode SNESTestLocalMin(SNES snes)
    5330: {
    5331:   PetscInt    N, i, j;
    5332:   Vec         u, uh, fh;
    5333:   PetscScalar value;
    5334:   PetscReal   norm;

    5336:   PetscFunctionBegin;
    5337:   PetscCall(SNESGetSolution(snes, &u));
    5338:   PetscCall(VecDuplicate(u, &uh));
    5339:   PetscCall(VecDuplicate(u, &fh));

    5341:   /* currently only works for sequential */
    5342:   PetscCall(PetscPrintf(PetscObjectComm((PetscObject)snes), "Testing FormFunction() for local min\n"));
    5343:   PetscCall(VecGetSize(u, &N));
    5344:   for (i = 0; i < N; i++) {
    5345:     PetscCall(VecCopy(u, uh));
    5346:     PetscCall(PetscPrintf(PetscObjectComm((PetscObject)snes), "i = %" PetscInt_FMT "\n", i));
    5347:     for (j = -10; j < 11; j++) {
    5348:       value = PetscSign(j) * PetscExpReal(PetscAbs(j) - 10.0);
    5349:       PetscCall(VecSetValue(uh, i, value, ADD_VALUES));
    5350:       PetscCall(SNESComputeFunction(snes, uh, fh));
    5351:       PetscCall(VecNorm(fh, NORM_2, &norm));
    5352:       PetscCall(PetscPrintf(PetscObjectComm((PetscObject)snes), "       j norm %" PetscInt_FMT " %18.16e\n", j, (double)norm));
    5353:       value = -value;
    5354:       PetscCall(VecSetValue(uh, i, value, ADD_VALUES));
    5355:     }
    5356:   }
    5357:   PetscCall(VecDestroy(&uh));
    5358:   PetscCall(VecDestroy(&fh));
    5359:   PetscFunctionReturn(PETSC_SUCCESS);
    5360: }

    5362: /*@
    5363:   SNESKSPSetUseEW - Sets `SNES` to the use Eisenstat-Walker method for
    5364:   computing relative tolerance for linear solvers within an inexact
    5365:   Newton method.

    5367:   Logically Collective

    5369:   Input Parameters:
    5370: + snes - `SNES` context
    5371: - flag - `PETSC_TRUE` or `PETSC_FALSE`

    5373:   Options Database Keys:
    5374: + -snes_ksp_ew                       - use Eisenstat-Walker method for determining linear system convergence
    5375: . -snes_ksp_ew_version ver           - version of  Eisenstat-Walker method
    5376: . -snes_ksp_ew_rtol0 <rtol0>         - Sets rtol0
    5377: . -snes_ksp_ew_rtolmax <rtolmax>     - Sets rtolmax
    5378: . -snes_ksp_ew_gamma <gamma>         - Sets gamma
    5379: . -snes_ksp_ew_alpha <alpha>         - Sets alpha
    5380: . -snes_ksp_ew_alpha2 <alpha2>       - Sets alpha2
    5381: - -snes_ksp_ew_threshold <threshold> - Sets threshold

    5383:   Level: advanced

    5385:   Note:
    5386:   The default is to use a constant relative tolerance for
    5387:   the inner linear solvers.  Alternatively, one can use the
    5388:   Eisenstat-Walker method {cite}`ew96`, where the relative convergence tolerance
    5389:   is reset at each Newton iteration according progress of the nonlinear
    5390:   solver.

    5392: .seealso: [](ch_snes), `KSP`, `SNES`, `SNESKSPGetUseEW()`, `SNESKSPGetParametersEW()`, `SNESKSPSetParametersEW()`
    5393: @*/
    5394: PetscErrorCode SNESKSPSetUseEW(SNES snes, PetscBool flag)
    5395: {
    5396:   PetscFunctionBegin;
    5399:   snes->ksp_ewconv = flag;
    5400:   PetscFunctionReturn(PETSC_SUCCESS);
    5401: }

    5403: /*@
    5404:   SNESKSPGetUseEW - Gets if `SNES` is using Eisenstat-Walker method
    5405:   for computing relative tolerance for linear solvers within an
    5406:   inexact Newton method.

    5408:   Not Collective

    5410:   Input Parameter:
    5411: . snes - `SNES` context

    5413:   Output Parameter:
    5414: . flag - `PETSC_TRUE` or `PETSC_FALSE`

    5416:   Level: advanced

    5418: .seealso: [](ch_snes), `SNESKSPSetUseEW()`, `SNESKSPGetParametersEW()`, `SNESKSPSetParametersEW()`
    5419: @*/
    5420: PetscErrorCode SNESKSPGetUseEW(SNES snes, PetscBool *flag)
    5421: {
    5422:   PetscFunctionBegin;
    5424:   PetscAssertPointer(flag, 2);
    5425:   *flag = snes->ksp_ewconv;
    5426:   PetscFunctionReturn(PETSC_SUCCESS);
    5427: }

    5429: /*@
    5430:   SNESKSPSetParametersEW - Sets parameters for Eisenstat-Walker
    5431:   convergence criteria for the linear solvers within an inexact
    5432:   Newton method.

    5434:   Logically Collective

    5436:   Input Parameters:
    5437: + snes      - `SNES` context
    5438: . version   - version 1, 2 (default is 2), 3 or 4
    5439: . rtol_0    - initial relative tolerance (0 <= rtol_0 < 1)
    5440: . rtol_max  - maximum relative tolerance (0 <= rtol_max < 1)
    5441: . gamma     - multiplicative factor for version 2 rtol computation
    5442:              (0 <= gamma2 <= 1)
    5443: . alpha     - power for version 2 rtol computation (1 < alpha <= 2)
    5444: . alpha2    - power for safeguard
    5445: - threshold - threshold for imposing safeguard (0 < threshold < 1)

    5447:   Level: advanced

    5449:   Notes:
    5450:   Version 3 was contributed by Luis Chacon, June 2006.

    5452:   Use `PETSC_CURRENT` to retain the default for any of the parameters.

    5454: .seealso: [](ch_snes), `SNES`, `SNESKSPSetUseEW()`, `SNESKSPGetUseEW()`, `SNESKSPGetParametersEW()`
    5455: @*/
    5456: PetscErrorCode SNESKSPSetParametersEW(SNES snes, PetscInt version, PetscReal rtol_0, PetscReal rtol_max, PetscReal gamma, PetscReal alpha, PetscReal alpha2, PetscReal threshold)
    5457: {
    5458:   SNESKSPEW *kctx;

    5460:   PetscFunctionBegin;
    5462:   kctx = (SNESKSPEW *)snes->kspconvctx;
    5463:   PetscCheck(kctx, PETSC_COMM_SELF, PETSC_ERR_ARG_WRONGSTATE, "No Eisenstat-Walker context existing");

    5472:   if (version != PETSC_CURRENT) kctx->version = version;
    5473:   if (rtol_0 != (PetscReal)PETSC_CURRENT) kctx->rtol_0 = rtol_0;
    5474:   if (rtol_max != (PetscReal)PETSC_CURRENT) kctx->rtol_max = rtol_max;
    5475:   if (gamma != (PetscReal)PETSC_CURRENT) kctx->gamma = gamma;
    5476:   if (alpha != (PetscReal)PETSC_CURRENT) kctx->alpha = alpha;
    5477:   if (alpha2 != (PetscReal)PETSC_CURRENT) kctx->alpha2 = alpha2;
    5478:   if (threshold != (PetscReal)PETSC_CURRENT) kctx->threshold = threshold;

    5480:   PetscCheck(kctx->version >= 1 && kctx->version <= 4, PETSC_COMM_SELF, PETSC_ERR_ARG_OUTOFRANGE, "Only versions 1 to 4 are supported: %" PetscInt_FMT, kctx->version);
    5481:   PetscCheck(kctx->rtol_0 >= 0.0 && kctx->rtol_0 < 1.0, PETSC_COMM_SELF, PETSC_ERR_ARG_OUTOFRANGE, "0.0 <= rtol_0 < 1.0: %g", (double)kctx->rtol_0);
    5482:   PetscCheck(kctx->rtol_max >= 0.0 && kctx->rtol_max < 1.0, PETSC_COMM_SELF, PETSC_ERR_ARG_OUTOFRANGE, "0.0 <= rtol_max (%g) < 1.0", (double)kctx->rtol_max);
    5483:   PetscCheck(kctx->gamma >= 0.0 && kctx->gamma <= 1.0, PETSC_COMM_SELF, PETSC_ERR_ARG_OUTOFRANGE, "0.0 <= gamma (%g) <= 1.0", (double)kctx->gamma);
    5484:   PetscCheck(kctx->alpha > 1.0 && kctx->alpha <= 2.0, PETSC_COMM_SELF, PETSC_ERR_ARG_OUTOFRANGE, "1.0 < alpha (%g) <= 2.0", (double)kctx->alpha);
    5485:   PetscCheck(kctx->threshold > 0.0 && kctx->threshold < 1.0, PETSC_COMM_SELF, PETSC_ERR_ARG_OUTOFRANGE, "0.0 < threshold (%g) < 1.0", (double)kctx->threshold);
    5486:   PetscFunctionReturn(PETSC_SUCCESS);
    5487: }

    5489: /*@
    5490:   SNESKSPGetParametersEW - Gets parameters for Eisenstat-Walker
    5491:   convergence criteria for the linear solvers within an inexact
    5492:   Newton method.

    5494:   Not Collective

    5496:   Input Parameter:
    5497: . snes - `SNES` context

    5499:   Output Parameters:
    5500: + version   - version 1, 2 (default is 2), 3 or 4
    5501: . rtol_0    - initial relative tolerance (0 <= rtol_0 < 1)
    5502: . rtol_max  - maximum relative tolerance (0 <= rtol_max < 1)
    5503: . gamma     - multiplicative factor for version 2 rtol computation (0 <= gamma2 <= 1)
    5504: . alpha     - power for version 2 rtol computation (1 < alpha <= 2)
    5505: . alpha2    - power for safeguard
    5506: - threshold - threshold for imposing safeguard (0 < threshold < 1)

    5508:   Level: advanced

    5510: .seealso: [](ch_snes), `SNES`, `SNESKSPSetUseEW()`, `SNESKSPGetUseEW()`, `SNESKSPSetParametersEW()`
    5511: @*/
    5512: PetscErrorCode SNESKSPGetParametersEW(SNES snes, PetscInt *version, PetscReal *rtol_0, PetscReal *rtol_max, PetscReal *gamma, PetscReal *alpha, PetscReal *alpha2, PetscReal *threshold)
    5513: {
    5514:   SNESKSPEW *kctx;

    5516:   PetscFunctionBegin;
    5518:   kctx = (SNESKSPEW *)snes->kspconvctx;
    5519:   PetscCheck(kctx, PETSC_COMM_SELF, PETSC_ERR_ARG_WRONGSTATE, "No Eisenstat-Walker context existing");
    5520:   if (version) *version = kctx->version;
    5521:   if (rtol_0) *rtol_0 = kctx->rtol_0;
    5522:   if (rtol_max) *rtol_max = kctx->rtol_max;
    5523:   if (gamma) *gamma = kctx->gamma;
    5524:   if (alpha) *alpha = kctx->alpha;
    5525:   if (alpha2) *alpha2 = kctx->alpha2;
    5526:   if (threshold) *threshold = kctx->threshold;
    5527:   PetscFunctionReturn(PETSC_SUCCESS);
    5528: }

    5530: PetscErrorCode KSPPreSolve_SNESEW(KSP ksp, Vec b, Vec x, void *ctx)
    5531: {
    5532:   SNES       snes = (SNES)ctx;
    5533:   SNESKSPEW *kctx = (SNESKSPEW *)snes->kspconvctx;
    5534:   PetscReal  rtol = PETSC_CURRENT, stol;

    5536:   PetscFunctionBegin;
    5537:   if (!snes->ksp_ewconv) PetscFunctionReturn(PETSC_SUCCESS);
    5538:   if (!snes->iter) {
    5539:     rtol = kctx->rtol_0; /* first time in, so use the original user rtol */
    5540:     PetscCall(VecNorm(snes->vec_func, NORM_2, &kctx->norm_first));
    5541:   } else {
    5542:     PetscCheck(kctx->version >= 1 && kctx->version <= 4, PETSC_COMM_SELF, PETSC_ERR_ARG_OUTOFRANGE, "Only versions 1-4 are supported: %" PetscInt_FMT, kctx->version);
    5543:     if (kctx->version == 1) {
    5544:       rtol = PetscAbsReal(snes->norm - kctx->lresid_last) / kctx->norm_last;
    5545:       stol = PetscPowReal(kctx->rtol_last, kctx->alpha2);
    5546:       if (stol > kctx->threshold) rtol = PetscMax(rtol, stol);
    5547:     } else if (kctx->version == 2) {
    5548:       rtol = kctx->gamma * PetscPowReal(snes->norm / kctx->norm_last, kctx->alpha);
    5549:       stol = kctx->gamma * PetscPowReal(kctx->rtol_last, kctx->alpha);
    5550:       if (stol > kctx->threshold) rtol = PetscMax(rtol, stol);
    5551:     } else if (kctx->version == 3) { /* contributed by Luis Chacon, June 2006. */
    5552:       rtol = kctx->gamma * PetscPowReal(snes->norm / kctx->norm_last, kctx->alpha);
    5553:       /* safeguard: avoid sharp decrease of rtol */
    5554:       stol = kctx->gamma * PetscPowReal(kctx->rtol_last, kctx->alpha);
    5555:       stol = PetscMax(rtol, stol);
    5556:       rtol = PetscMin(kctx->rtol_0, stol);
    5557:       /* safeguard: avoid oversolving */
    5558:       stol = kctx->gamma * (kctx->norm_first * snes->rtol) / snes->norm;
    5559:       stol = PetscMax(rtol, stol);
    5560:       rtol = PetscMin(kctx->rtol_0, stol);
    5561:     } else /* if (kctx->version == 4) */ {
    5562:       /* H.-B. An et al. Journal of Computational and Applied Mathematics 200 (2007) 47-60 */
    5563:       PetscReal ared = PetscAbsReal(kctx->norm_last - snes->norm);
    5564:       PetscReal pred = PetscAbsReal(kctx->norm_last - kctx->lresid_last);
    5565:       PetscReal rk   = ared / pred;
    5566:       if (rk < kctx->v4_p1) rtol = 1. - 2. * kctx->v4_p1;
    5567:       else if (rk < kctx->v4_p2) rtol = kctx->rtol_last;
    5568:       else if (rk < kctx->v4_p3) rtol = kctx->v4_m1 * kctx->rtol_last;
    5569:       else rtol = kctx->v4_m2 * kctx->rtol_last;

    5571:       if (kctx->rtol_last_2 > kctx->v4_m3 && kctx->rtol_last > kctx->v4_m3 && kctx->rk_last_2 < kctx->v4_p1 && kctx->rk_last < kctx->v4_p1) rtol = kctx->v4_m4 * kctx->rtol_last;
    5572:       kctx->rtol_last_2 = kctx->rtol_last;
    5573:       kctx->rk_last_2   = kctx->rk_last;
    5574:       kctx->rk_last     = rk;
    5575:     }
    5576:   }
    5577:   /* safeguard: avoid rtol greater than rtol_max */
    5578:   rtol = PetscMin(rtol, kctx->rtol_max);
    5579:   PetscCall(KSPSetTolerances(ksp, rtol, PETSC_CURRENT, PETSC_CURRENT, PETSC_CURRENT));
    5580:   PetscCall(PetscInfo(snes, "iter %" PetscInt_FMT ", Eisenstat-Walker (version %" PetscInt_FMT ") KSP rtol=%g\n", snes->iter, kctx->version, (double)rtol));
    5581:   PetscFunctionReturn(PETSC_SUCCESS);
    5582: }

    5584: PetscErrorCode KSPPostSolve_SNESEW(KSP ksp, Vec b, Vec x, void *ctx)
    5585: {
    5586:   SNES       snes = (SNES)ctx;
    5587:   SNESKSPEW *kctx = (SNESKSPEW *)snes->kspconvctx;
    5588:   PCSide     pcside;
    5589:   Vec        lres;

    5591:   PetscFunctionBegin;
    5592:   if (!snes->ksp_ewconv) PetscFunctionReturn(PETSC_SUCCESS);
    5593:   PetscCall(KSPGetTolerances(ksp, &kctx->rtol_last, NULL, NULL, NULL));
    5594:   kctx->norm_last = snes->norm;
    5595:   if (kctx->version == 1 || kctx->version == 4) {
    5596:     PC        pc;
    5597:     PetscBool getRes;

    5599:     PetscCall(KSPGetPC(ksp, &pc));
    5600:     PetscCall(PetscObjectTypeCompare((PetscObject)pc, PCNONE, &getRes));
    5601:     if (!getRes) {
    5602:       KSPNormType normtype;

    5604:       PetscCall(KSPGetNormType(ksp, &normtype));
    5605:       getRes = (PetscBool)(normtype == KSP_NORM_UNPRECONDITIONED);
    5606:     }
    5607:     PetscCall(KSPGetPCSide(ksp, &pcside));
    5608:     if (pcside == PC_RIGHT || getRes) { /* KSP residual is true linear residual */
    5609:       PetscCall(KSPGetResidualNorm(ksp, &kctx->lresid_last));
    5610:     } else {
    5611:       /* KSP residual is preconditioned residual */
    5612:       /* compute true linear residual norm */
    5613:       Mat J;
    5614:       PetscCall(KSPGetOperators(ksp, &J, NULL));
    5615:       PetscCall(VecDuplicate(b, &lres));
    5616:       PetscCall(MatMult(J, x, lres));
    5617:       PetscCall(VecAYPX(lres, -1.0, b));
    5618:       PetscCall(VecNorm(lres, NORM_2, &kctx->lresid_last));
    5619:       PetscCall(VecDestroy(&lres));
    5620:     }
    5621:   }
    5622:   PetscFunctionReturn(PETSC_SUCCESS);
    5623: }

    5625: /*@
    5626:   SNESGetKSP - Returns the `KSP` context for a `SNES` solver.

    5628:   Not Collective, but if `snes` is parallel, then `ksp` is parallel

    5630:   Input Parameter:
    5631: . snes - the `SNES` context

    5633:   Output Parameter:
    5634: . ksp - the `KSP` context

    5636:   Level: beginner

    5638:   Notes:
    5639:   The user can then directly manipulate the `KSP` context to set various
    5640:   options, etc.  Likewise, the user can then extract and manipulate the
    5641:   `PC` contexts as well.

    5643:   Some `SNESType`s do not use a `KSP` but a `KSP` is still returned by this function, changes to that `KSP` will have no effect.

    5645: .seealso: [](ch_snes), `SNES`, `KSP`, `PC`, `KSPGetPC()`, `SNESCreate()`, `KSPCreate()`, `SNESSetKSP()`
    5646: @*/
    5647: PetscErrorCode SNESGetKSP(SNES snes, KSP *ksp)
    5648: {
    5649:   PetscFunctionBegin;
    5651:   PetscAssertPointer(ksp, 2);

    5653:   if (!snes->ksp) {
    5654:     PetscCall(KSPCreate(PetscObjectComm((PetscObject)snes), &snes->ksp));
    5655:     PetscCall(PetscObjectIncrementTabLevel((PetscObject)snes->ksp, (PetscObject)snes, 1));

    5657:     PetscCall(KSPSetPreSolve(snes->ksp, KSPPreSolve_SNESEW, snes));
    5658:     PetscCall(KSPSetPostSolve(snes->ksp, KSPPostSolve_SNESEW, snes));

    5660:     PetscCall(KSPMonitorSetFromOptions(snes->ksp, "-snes_monitor_ksp", "snes_preconditioned_residual", snes));
    5661:     PetscCall(PetscObjectSetOptions((PetscObject)snes->ksp, ((PetscObject)snes)->options));
    5662:   }
    5663:   *ksp = snes->ksp;
    5664:   PetscFunctionReturn(PETSC_SUCCESS);
    5665: }

    5667: #include <petsc/private/dmimpl.h>
    5668: /*@
    5669:   SNESSetDM - Sets the `DM` that may be used by some `SNES` nonlinear solvers or their underlying preconditioners

    5671:   Logically Collective

    5673:   Input Parameters:
    5674: + snes - the nonlinear solver context
    5675: - dm   - the `DM`, cannot be `NULL`

    5677:   Level: intermediate

    5679:   Note:
    5680:   A `DM` can only be used for solving one problem at a time because information about the problem is stored on the `DM`,
    5681:   even when not using interfaces like `DMSNESSetFunction()`.  Use `DMClone()` to get a distinct `DM` when solving different
    5682:   problems using the same function space.

    5684: .seealso: [](ch_snes), `DM`, `SNES`, `SNESGetDM()`, `KSPSetDM()`, `KSPGetDM()`
    5685: @*/
    5686: PetscErrorCode SNESSetDM(SNES snes, DM dm)
    5687: {
    5688:   KSP    ksp;
    5689:   DMSNES sdm;

    5691:   PetscFunctionBegin;
    5694:   PetscCall(PetscObjectReference((PetscObject)dm));
    5695:   if (snes->dm) { /* Move the DMSNES context over to the new DM unless the new DM already has one */
    5696:     if (snes->dm->dmsnes && !dm->dmsnes) {
    5697:       PetscCall(DMCopyDMSNES(snes->dm, dm));
    5698:       PetscCall(DMGetDMSNES(snes->dm, &sdm));
    5699:       if (sdm->originaldm == snes->dm) sdm->originaldm = dm; /* Grant write privileges to the replacement DM */
    5700:     }
    5701:     PetscCall(DMCoarsenHookRemove(snes->dm, DMCoarsenHook_SNESVecSol, DMRestrictHook_SNESVecSol, snes));
    5702:     PetscCall(DMDestroy(&snes->dm));
    5703:   }
    5704:   snes->dm     = dm;
    5705:   snes->dmAuto = PETSC_FALSE;

    5707:   PetscCall(SNESGetKSP(snes, &ksp));
    5708:   PetscCall(KSPSetDM(ksp, dm));
    5709:   PetscCall(KSPSetDMActive(ksp, PETSC_FALSE));
    5710:   if (snes->npc) {
    5711:     PetscCall(SNESSetDM(snes->npc, snes->dm));
    5712:     PetscCall(SNESSetNPCSide(snes, snes->npcside));
    5713:   }
    5714:   PetscFunctionReturn(PETSC_SUCCESS);
    5715: }

    5717: /*@
    5718:   SNESGetDM - Gets the `DM` that may be used by some `SNES` nonlinear solvers/preconditioners

    5720:   Not Collective but `dm` obtained is parallel on `snes`

    5722:   Input Parameter:
    5723: . snes - the `SNES` context

    5725:   Output Parameter:
    5726: . dm - the `DM`

    5728:   Level: intermediate

    5730: .seealso: [](ch_snes), `DM`, `SNES`, `SNESSetDM()`, `KSPSetDM()`, `KSPGetDM()`
    5731: @*/
    5732: PetscErrorCode SNESGetDM(SNES snes, DM *dm)
    5733: {
    5734:   PetscFunctionBegin;
    5736:   if (!snes->dm) {
    5737:     PetscCall(DMShellCreate(PetscObjectComm((PetscObject)snes), &snes->dm));
    5738:     snes->dmAuto = PETSC_TRUE;
    5739:   }
    5740:   *dm = snes->dm;
    5741:   PetscFunctionReturn(PETSC_SUCCESS);
    5742: }

    5744: /*@
    5745:   SNESSetNPC - Sets the nonlinear preconditioner to be used.

    5747:   Collective

    5749:   Input Parameters:
    5750: + snes - iterative context obtained from `SNESCreate()`
    5751: - npc  - the `SNES` nonlinear preconditioner object

    5753:   Options Database Key:
    5754: . -npc_snes_type <type> - set the type of the `SNES` to use as the nonlinear preconditioner

    5756:   Level: developer

    5758:   Notes:
    5759:   This is rarely used, rather use `SNESGetNPC()` to retrieve the preconditioner and configure it using the API.

    5761:   Only some `SNESType` can use a nonlinear preconditioner

    5763: .seealso: [](ch_snes), `SNES`, `SNESNGS`, `SNESFAS`, `SNESGetNPC()`, `SNESHasNPC()`
    5764: @*/
    5765: PetscErrorCode SNESSetNPC(SNES snes, SNES npc)
    5766: {
    5767:   PetscFunctionBegin;
    5770:   PetscCheckSameComm(snes, 1, npc, 2);
    5771:   PetscCall(PetscObjectReference((PetscObject)npc));
    5772:   PetscCall(SNESDestroy(&snes->npc));
    5773:   snes->npc = npc;
    5774:   PetscFunctionReturn(PETSC_SUCCESS);
    5775: }

    5777: /*@
    5778:   SNESGetNPC - Gets a nonlinear preconditioning solver SNES` to be used to precondition the original nonlinear solver.

    5780:   Not Collective; but any changes to the obtained the `pc` object must be applied collectively

    5782:   Input Parameter:
    5783: . snes - iterative context obtained from `SNESCreate()`

    5785:   Output Parameter:
    5786: . pc - the `SNES` preconditioner context

    5788:   Options Database Key:
    5789: . -npc_snes_type <type> - set the type of the `SNES` to use as the nonlinear preconditioner

    5791:   Level: advanced

    5793:   Notes:
    5794:   If a `SNES` was previously set with `SNESSetNPC()` then that value is returned, otherwise a new `SNES` object is created that will
    5795:   be used as the nonlinear preconditioner for the current `SNES`.

    5797:   The (preconditioner) `SNES` returned automatically inherits the same nonlinear function and Jacobian supplied to the original
    5798:   `SNES`. These may be overwritten if needed.

    5800:   Use the options database prefixes `-npc_snes`, `-npc_ksp`, etc., to control the configuration of the nonlinear preconditioner

    5802: .seealso: [](ch_snes), `SNESSetNPC()`, `SNESHasNPC()`, `SNES`, `SNESCreate()`
    5803: @*/
    5804: PetscErrorCode SNESGetNPC(SNES snes, SNES *pc)
    5805: {
    5806:   const char *optionsprefix;

    5808:   PetscFunctionBegin;
    5810:   PetscAssertPointer(pc, 2);
    5811:   if (!snes->npc) {
    5812:     void *ctx;

    5814:     PetscCall(SNESCreate(PetscObjectComm((PetscObject)snes), &snes->npc));
    5815:     PetscCall(PetscObjectIncrementTabLevel((PetscObject)snes->npc, (PetscObject)snes, 1));
    5816:     PetscCall(SNESGetOptionsPrefix(snes, &optionsprefix));
    5817:     PetscCall(SNESSetOptionsPrefix(snes->npc, optionsprefix));
    5818:     PetscCall(SNESAppendOptionsPrefix(snes->npc, "npc_"));
    5819:     if (snes->ops->usercompute) {
    5820:       PetscCall(SNESSetComputeApplicationContext(snes, snes->ops->usercompute, snes->ops->ctxdestroy));
    5821:     } else {
    5822:       PetscCall(SNESGetApplicationContext(snes, &ctx));
    5823:       PetscCall(SNESSetApplicationContext(snes->npc, ctx));
    5824:     }
    5825:     PetscCall(SNESSetCountersReset(snes->npc, PETSC_FALSE));
    5826:   }
    5827:   *pc = snes->npc;
    5828:   PetscFunctionReturn(PETSC_SUCCESS);
    5829: }

    5831: /*@
    5832:   SNESHasNPC - Returns whether a nonlinear preconditioner is associated with the given `SNES`

    5834:   Not Collective

    5836:   Input Parameter:
    5837: . snes - iterative context obtained from `SNESCreate()`

    5839:   Output Parameter:
    5840: . has_npc - whether the `SNES` has a nonlinear preconditioner or not

    5842:   Level: developer

    5844: .seealso: [](ch_snes), `SNESSetNPC()`, `SNESGetNPC()`
    5845: @*/
    5846: PetscErrorCode SNESHasNPC(SNES snes, PetscBool *has_npc)
    5847: {
    5848:   PetscFunctionBegin;
    5850:   PetscAssertPointer(has_npc, 2);
    5851:   *has_npc = snes->npc ? PETSC_TRUE : PETSC_FALSE;
    5852:   PetscFunctionReturn(PETSC_SUCCESS);
    5853: }

    5855: /*@
    5856:   SNESSetNPCSide - Sets the nonlinear preconditioning side used by the nonlinear preconditioner inside `SNES`.

    5858:   Logically Collective

    5860:   Input Parameter:
    5861: . snes - iterative context obtained from `SNESCreate()`

    5863:   Output Parameter:
    5864: . side - the preconditioning side, where side is one of
    5865: .vb
    5866:       PC_LEFT  - left preconditioning
    5867:       PC_RIGHT - right preconditioning (default for most nonlinear solvers)
    5868: .ve

    5870:   Options Database Key:
    5871: . -snes_npc_side <right,left> - nonlinear preconditioner side

    5873:   Level: intermediate

    5875:   Note:
    5876:   `SNESNRICHARDSON` and `SNESNCG` only support left preconditioning.

    5878: .seealso: [](ch_snes), `SNES`, `SNESGetNPC()`, `SNESNRICHARDSON`, `SNESNCG`, `SNESType`, `SNESGetNPCSide()`, `KSPSetPCSide()`, `PC_LEFT`, `PC_RIGHT`, `PCSide`
    5879: @*/
    5880: PetscErrorCode SNESSetNPCSide(SNES snes, PCSide side)
    5881: {
    5882:   PetscFunctionBegin;
    5885:   if (side == PC_SIDE_DEFAULT) side = PC_RIGHT;
    5886:   PetscCheck((side == PC_LEFT) || (side == PC_RIGHT), PetscObjectComm((PetscObject)snes), PETSC_ERR_ARG_WRONG, "Only PC_LEFT and PC_RIGHT are supported");
    5887:   snes->npcside = side;
    5888:   PetscFunctionReturn(PETSC_SUCCESS);
    5889: }

    5891: /*@
    5892:   SNESGetNPCSide - Gets the preconditioning side used by the nonlinear preconditioner inside `SNES`.

    5894:   Not Collective

    5896:   Input Parameter:
    5897: . snes - iterative context obtained from `SNESCreate()`

    5899:   Output Parameter:
    5900: . side - the preconditioning side, where side is one of
    5901: .vb
    5902:       `PC_LEFT` - left preconditioning
    5903:       `PC_RIGHT` - right preconditioning (default for most nonlinear solvers)
    5904: .ve

    5906:   Level: intermediate

    5908: .seealso: [](ch_snes), `SNES`, `SNESGetNPC()`, `SNESSetNPCSide()`, `KSPGetPCSide()`, `PC_LEFT`, `PC_RIGHT`, `PCSide`
    5909: @*/
    5910: PetscErrorCode SNESGetNPCSide(SNES snes, PCSide *side)
    5911: {
    5912:   PetscFunctionBegin;
    5914:   PetscAssertPointer(side, 2);
    5915:   *side = snes->npcside;
    5916:   PetscFunctionReturn(PETSC_SUCCESS);
    5917: }

    5919: /*@
    5920:   SNESSetLineSearch - Sets the `SNESLineSearch` to be used for a given `SNES`

    5922:   Collective

    5924:   Input Parameters:
    5925: + snes       - iterative context obtained from `SNESCreate()`
    5926: - linesearch - the linesearch object

    5928:   Level: developer

    5930:   Note:
    5931:   This is almost never used, rather one uses `SNESGetLineSearch()` to retrieve the line search and set options on it
    5932:   to configure it using the API).

    5934: .seealso: [](ch_snes), `SNES`, `SNESLineSearch`, `SNESGetLineSearch()`
    5935: @*/
    5936: PetscErrorCode SNESSetLineSearch(SNES snes, SNESLineSearch linesearch)
    5937: {
    5938:   PetscFunctionBegin;
    5941:   PetscCheckSameComm(snes, 1, linesearch, 2);
    5942:   PetscCall(PetscObjectReference((PetscObject)linesearch));
    5943:   PetscCall(SNESLineSearchDestroy(&snes->linesearch));

    5945:   snes->linesearch = linesearch;
    5946:   PetscFunctionReturn(PETSC_SUCCESS);
    5947: }

    5949: /*@
    5950:   SNESGetLineSearch - Returns the line search associated with the `SNES`.

    5952:   Not Collective

    5954:   Input Parameter:
    5955: . snes - iterative context obtained from `SNESCreate()`

    5957:   Output Parameter:
    5958: . linesearch - linesearch context

    5960:   Level: beginner

    5962:   Notes:
    5963:   It creates a default line search instance which can be configured as needed in case it has not been already set with `SNESSetLineSearch()`.

    5965:   You can also use the options database keys `-snes_linesearch_*` to configure the line search. See `SNESLineSearchSetFromOptions()` for the possible options.

    5967: .seealso: [](ch_snes), `SNESLineSearch`, `SNESSetLineSearch()`, `SNESLineSearchCreate()`, `SNESLineSearchSetFromOptions()`
    5968: @*/
    5969: PetscErrorCode SNESGetLineSearch(SNES snes, SNESLineSearch *linesearch)
    5970: {
    5971:   const char *optionsprefix;

    5973:   PetscFunctionBegin;
    5975:   PetscAssertPointer(linesearch, 2);
    5976:   if (!snes->linesearch) {
    5977:     PetscCall(SNESGetOptionsPrefix(snes, &optionsprefix));
    5978:     PetscCall(SNESLineSearchCreate(PetscObjectComm((PetscObject)snes), &snes->linesearch));
    5979:     PetscCall(SNESLineSearchSetSNES(snes->linesearch, snes));
    5980:     PetscCall(SNESLineSearchAppendOptionsPrefix(snes->linesearch, optionsprefix));
    5981:     PetscCall(PetscObjectIncrementTabLevel((PetscObject)snes->linesearch, (PetscObject)snes, 1));
    5982:   }
    5983:   *linesearch = snes->linesearch;
    5984:   PetscFunctionReturn(PETSC_SUCCESS);
    5985: }