Date: 2026-03-01T05:24:48+00:00

Actual source code: itcreate.c

      1: /*
      2:      The basic KSP routines, Create, View etc. are here.
      3: */
      4: #include <petsc/private/kspimpl.h>

      6: /* Logging support */
      7: PetscClassId  KSP_CLASSID;
      8: PetscClassId  DMKSP_CLASSID;
      9: PetscClassId  KSPGUESS_CLASSID;
     10: PetscLogEvent KSP_GMRESOrthogonalization, KSP_SetUp, KSP_Solve, KSP_SolveTranspose, KSP_MatSolve, KSP_MatSolveTranspose;

     12: /*
     13:    Contains the list of registered KSP routines
     14: */
     15: PetscFunctionList KSPList              = NULL;
     16: PetscBool         KSPRegisterAllCalled = PETSC_FALSE;

     18: /*
     19:    Contains the list of registered KSP monitors
     20: */
     21: PetscFunctionList KSPMonitorList              = NULL;
     22: PetscFunctionList KSPMonitorCreateList        = NULL;
     23: PetscFunctionList KSPMonitorDestroyList       = NULL;
     24: PetscBool         KSPMonitorRegisterAllCalled = PETSC_FALSE;

     26: /*@
     27:   KSPLoad - Loads a `KSP` that has been stored in a `PETSCVIEWERBINARY`  with `KSPView()`.

     29:   Collective

     31:   Input Parameters:
     32: + newdm  - the newly loaded `KSP`, this needs to have been created with `KSPCreate()` or
     33:            some related function before a call to `KSPLoad()`.
     34: - viewer - binary file viewer, obtained from `PetscViewerBinaryOpen()`

     36:   Level: intermediate

     38:   Note:
     39:   The type is determined by the data in the file, any type set into the `KSP` before this call is ignored.

     41: .seealso: [](ch_ksp), `KSP`, `PetscViewerBinaryOpen()`, `KSPView()`, `MatLoad()`, `VecLoad()`
     42: @*/
     43: PetscErrorCode KSPLoad(KSP newdm, PetscViewer viewer)
     44: {
     45:   PetscBool isbinary;
     46:   PetscInt  classid;
     47:   char      type[256];
     48:   PC        pc;

     50:   PetscFunctionBegin;
     53:   PetscCall(PetscObjectTypeCompare((PetscObject)viewer, PETSCVIEWERBINARY, &isbinary));
     54:   PetscCheck(isbinary, PETSC_COMM_SELF, PETSC_ERR_ARG_WRONG, "Invalid viewer; open viewer with PetscViewerBinaryOpen()");

     56:   PetscCall(PetscViewerBinaryRead(viewer, &classid, 1, NULL, PETSC_INT));
     57:   PetscCheck(classid == KSP_FILE_CLASSID, PetscObjectComm((PetscObject)newdm), PETSC_ERR_ARG_WRONG, "Not KSP next in file");
     58:   PetscCall(PetscViewerBinaryRead(viewer, type, 256, NULL, PETSC_CHAR));
     59:   PetscCall(KSPSetType(newdm, type));
     60:   PetscTryTypeMethod(newdm, load, viewer);
     61:   PetscCall(KSPGetPC(newdm, &pc));
     62:   PetscCall(PCLoad(pc, viewer));
     63:   PetscFunctionReturn(PETSC_SUCCESS);
     64: }

     66: #include <petscdraw.h>
     67: #if defined(PETSC_HAVE_SAWS)
     68: #include <petscviewersaws.h>
     69: #endif
     70: /*@
     71:   KSPView - Prints the various parameters currently set in the `KSP` object. For example, the convergence tolerances and `KSPType`.
     72:   Also views the `PC` and `Mat` contained by the `KSP` with `PCView()` and `MatView()`.

     74:   Collective

     76:   Input Parameters:
     77: + ksp    - the Krylov space context
     78: - viewer - visualization context

     80:   Options Database Key:
     81: . -ksp_view - print the `KSP` data structure at the end of each `KSPSolve()` call

     83:   Level: beginner

     85:   Notes:
     86:   The available visualization contexts include
     87: +     `PETSC_VIEWER_STDOUT_SELF` - standard output (default)
     88: -     `PETSC_VIEWER_STDOUT_WORLD` - synchronized standard
     89:   output where only the first processor opens
     90:   the file.  All other processors send their
     91:   data to the first processor to print.

     93:   The available formats include
     94: +     `PETSC_VIEWER_DEFAULT` - standard output (default)
     95: -     `PETSC_VIEWER_ASCII_INFO_DETAIL` - more verbose output for `PCBJACOBI` and `PCASM`

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

    100:   Use `KSPViewFromOptions()` to allow the user to select many different `PetscViewerType` and formats from the options database.

    102:   In the debugger you can do call `KSPView(ksp,0)` to display the `KSP`. (The same holds for any PETSc object viewer).

    104: .seealso: [](ch_ksp), `KSP`, `PetscViewer`, `PCView()`, `PetscViewerASCIIOpen()`, `KSPViewFromOptions()`
    105: @*/
    106: PetscErrorCode KSPView(KSP ksp, PetscViewer viewer)
    107: {
    108:   PetscBool isascii, isbinary, isdraw, isstring;
    109: #if defined(PETSC_HAVE_SAWS)
    110:   PetscBool issaws;
    111: #endif

    113:   PetscFunctionBegin;
    115:   if (!viewer) PetscCall(PetscViewerASCIIGetStdout(PetscObjectComm((PetscObject)ksp), &viewer));
    117:   PetscCheckSameComm(ksp, 1, viewer, 2);

    119:   PetscCall(PetscObjectTypeCompare((PetscObject)viewer, PETSCVIEWERASCII, &isascii));
    120:   PetscCall(PetscObjectTypeCompare((PetscObject)viewer, PETSCVIEWERBINARY, &isbinary));
    121:   PetscCall(PetscObjectTypeCompare((PetscObject)viewer, PETSCVIEWERDRAW, &isdraw));
    122:   PetscCall(PetscObjectTypeCompare((PetscObject)viewer, PETSCVIEWERSTRING, &isstring));
    123: #if defined(PETSC_HAVE_SAWS)
    124:   PetscCall(PetscObjectTypeCompare((PetscObject)viewer, PETSCVIEWERSAWS, &issaws));
    125: #endif
    126:   if (isascii) {
    127:     PetscCall(PetscObjectPrintClassNamePrefixType((PetscObject)ksp, viewer));
    128:     PetscCall(PetscViewerASCIIPushTab(viewer));
    129:     PetscTryTypeMethod(ksp, view, viewer);
    130:     PetscCall(PetscViewerASCIIPopTab(viewer));
    131:     if (ksp->guess_zero) {
    132:       PetscCall(PetscViewerASCIIPrintf(viewer, "  maximum iterations=%" PetscInt_FMT ", initial guess is zero\n", ksp->max_it));
    133:     } else {
    134:       PetscCall(PetscViewerASCIIPrintf(viewer, "  maximum iterations=%" PetscInt_FMT ", nonzero initial guess\n", ksp->max_it));
    135:     }
    136:     if (ksp->min_it) PetscCall(PetscViewerASCIIPrintf(viewer, "  minimum iterations=%" PetscInt_FMT "\n", ksp->min_it));
    137:     if (ksp->guess_knoll) PetscCall(PetscViewerASCIIPrintf(viewer, "  using preconditioner applied to right-hand side for initial guess\n"));
    138:     PetscCall(PetscViewerASCIIPrintf(viewer, "  tolerances: relative=%g, absolute=%g, divergence=%g\n", (double)ksp->rtol, (double)ksp->abstol, (double)ksp->divtol));
    139:     if (ksp->pc_side == PC_RIGHT) {
    140:       PetscCall(PetscViewerASCIIPrintf(viewer, "  right preconditioning\n"));
    141:     } else if (ksp->pc_side == PC_SYMMETRIC) {
    142:       PetscCall(PetscViewerASCIIPrintf(viewer, "  symmetric preconditioning\n"));
    143:     } else {
    144:       PetscCall(PetscViewerASCIIPrintf(viewer, "  left preconditioning\n"));
    145:     }
    146:     if (ksp->guess) {
    147:       PetscCall(PetscViewerASCIIPushTab(viewer));
    148:       PetscCall(KSPGuessView(ksp->guess, viewer));
    149:       PetscCall(PetscViewerASCIIPopTab(viewer));
    150:     }
    151:     if (ksp->dscale) PetscCall(PetscViewerASCIIPrintf(viewer, "  diagonally scaled system\n"));
    152:     PetscCall(PetscViewerASCIIPrintf(viewer, "  using %s norm type for convergence test\n", KSPNormTypes[ksp->normtype]));
    153:   } else if (isbinary) {
    154:     PetscInt    classid = KSP_FILE_CLASSID;
    155:     MPI_Comm    comm;
    156:     PetscMPIInt rank;
    157:     char        type[256];

    159:     PetscCall(PetscObjectGetComm((PetscObject)ksp, &comm));
    160:     PetscCallMPI(MPI_Comm_rank(comm, &rank));
    161:     if (rank == 0) {
    162:       PetscCall(PetscViewerBinaryWrite(viewer, &classid, 1, PETSC_INT));
    163:       PetscCall(PetscStrncpy(type, ((PetscObject)ksp)->type_name, 256));
    164:       PetscCall(PetscViewerBinaryWrite(viewer, type, 256, PETSC_CHAR));
    165:     }
    166:     PetscTryTypeMethod(ksp, view, viewer);
    167:   } else if (isstring) {
    168:     const char *type;
    169:     PetscCall(KSPGetType(ksp, &type));
    170:     PetscCall(PetscViewerStringSPrintf(viewer, " KSPType: %-7.7s", type));
    171:     PetscTryTypeMethod(ksp, view, viewer);
    172:   } else if (isdraw) {
    173:     PetscDraw draw;
    174:     char      str[36];
    175:     PetscReal x, y, bottom, h;
    176:     PetscBool flg;

    178:     PetscCall(PetscViewerDrawGetDraw(viewer, 0, &draw));
    179:     PetscCall(PetscDrawGetCurrentPoint(draw, &x, &y));
    180:     PetscCall(PetscObjectTypeCompare((PetscObject)ksp, KSPPREONLY, &flg));
    181:     if (!flg) {
    182:       PetscCall(PetscStrncpy(str, "KSP: ", sizeof(str)));
    183:       PetscCall(PetscStrlcat(str, ((PetscObject)ksp)->type_name, sizeof(str)));
    184:       PetscCall(PetscDrawStringBoxed(draw, x, y, PETSC_DRAW_RED, PETSC_DRAW_BLACK, str, NULL, &h));
    185:       bottom = y - h;
    186:     } else {
    187:       bottom = y;
    188:     }
    189:     PetscCall(PetscDrawPushCurrentPoint(draw, x, bottom));
    190: #if defined(PETSC_HAVE_SAWS)
    191:   } else if (issaws) {
    192:     PetscMPIInt rank;
    193:     const char *name;

    195:     PetscCall(PetscObjectGetName((PetscObject)ksp, &name));
    196:     PetscCallMPI(MPI_Comm_rank(PETSC_COMM_WORLD, &rank));
    197:     if (!((PetscObject)ksp)->amsmem && rank == 0) {
    198:       char dir[1024];

    200:       PetscCall(PetscObjectViewSAWs((PetscObject)ksp, viewer));
    201:       PetscCall(PetscSNPrintf(dir, 1024, "/PETSc/Objects/%s/its", name));
    202:       PetscCallSAWs(SAWs_Register, (dir, &ksp->its, 1, SAWs_READ, SAWs_INT));
    203:       if (!ksp->res_hist) PetscCall(KSPSetResidualHistory(ksp, NULL, PETSC_DECIDE, PETSC_TRUE));
    204:       PetscCall(PetscSNPrintf(dir, 1024, "/PETSc/Objects/%s/res_hist", name));
    205:       PetscCallSAWs(SAWs_Register, (dir, ksp->res_hist, 10, SAWs_READ, SAWs_DOUBLE));
    206:     }
    207: #endif
    208:   } else PetscTryTypeMethod(ksp, view, viewer);
    209:   if (ksp->pc) PetscCall(PCView(ksp->pc, viewer));
    210:   if (isdraw) {
    211:     PetscDraw draw;
    212:     PetscCall(PetscViewerDrawGetDraw(viewer, 0, &draw));
    213:     PetscCall(PetscDrawPopCurrentPoint(draw));
    214:   }
    215:   PetscFunctionReturn(PETSC_SUCCESS);
    216: }

    218: /*@
    219:   KSPViewFromOptions - View (print) a `KSP` object based on values in the options database. Also views the `PC` and `Mat` contained by the `KSP`
    220:   with `PCView()` and `MatView()`.

    222:   Collective

    224:   Input Parameters:
    225: + A    - Krylov solver context
    226: . obj  - Optional object that provides the options prefix used to query the options database
    227: - name - command line option

    229:   Level: intermediate

    231: .seealso: [](ch_ksp), `KSP`, `KSPView()`, `PetscObjectViewFromOptions()`, `KSPCreate()`
    232: @*/
    233: PetscErrorCode KSPViewFromOptions(KSP A, PetscObject obj, const char name[])
    234: {
    235:   PetscFunctionBegin;
    237:   PetscCall(PetscObjectViewFromOptions((PetscObject)A, obj, name));
    238:   PetscFunctionReturn(PETSC_SUCCESS);
    239: }

    241: /*@
    242:   KSPSetNormType - Sets the type of residual norm that is used for convergence testing in `KSPSolve()` for the given `KSP` context

    244:   Logically Collective

    246:   Input Parameters:
    247: + ksp      - Krylov solver context
    248: - normtype - one of
    249: .vb
    250:    KSP_NORM_NONE             - skips computing the norm, this should generally only be used if you are using
    251:                                the Krylov method as a smoother with a fixed small number of iterations.
    252:                                Implicitly sets `KSPConvergedSkip()` as the `KSP` convergence test.
    253:                                Note that certain algorithms such as `KSPGMRES` ALWAYS require the norm calculation,
    254:                                for these methods the norms are still computed, they are just not used in
    255:                                the convergence test.
    256:    KSP_NORM_PRECONDITIONED   - the default for left-preconditioned solves, uses the 2-norm
    257:                                of the preconditioned residual  $B^{-1}(b - A x)$.
    258:    KSP_NORM_UNPRECONDITIONED - uses the 2-norm of the true $b - Ax$ residual.
    259:    KSP_NORM_NATURAL          - uses the $A$ norm of the true $b - Ax$ residual; supported by `KSPCG`, `KSPCR`, `KSPCGNE`, `KSPCGS`
    260: .ve

    262:   Options Database Key:
    263: . -ksp_norm_type <none,preconditioned,unpreconditioned,natural> - set `KSP` norm type

    265:   Level: advanced

    267:   Notes:
    268:   The norm is always of the equations residual $\| b - A x^n \|$  (or an approximation to that norm), they are never a norm of the error in the equation.

    270:   Not all combinations of preconditioner side (see `KSPSetPCSide()`) and norm types are supported by all Krylov methods.
    271:   If only one is set, PETSc tries to automatically change the other to find a compatible pair.  If no such combination
    272:   is supported, PETSc will generate an error.

    274:   Developer Note:
    275:   Supported combinations of norm and preconditioner side are set using `KSPSetSupportedNorm()` for each `KSPType`.

    277: .seealso: [](ch_ksp), `KSPSetUp()`, `KSPSolve()`, `KSPDestroy()`, `KSPConvergedSkip()`, `KSPSetCheckNormIteration()`, `KSPSetPCSide()`, `KSPGetPCSide()`, `KSPNormType`
    278: @*/
    279: PetscErrorCode KSPSetNormType(KSP ksp, KSPNormType normtype)
    280: {
    281:   PetscFunctionBegin;
    284:   ksp->normtype = ksp->normtype_set = normtype;
    285:   PetscFunctionReturn(PETSC_SUCCESS);
    286: }

    288: /*@
    289:   KSPSetCheckNormIteration - Sets the first iteration at which the norm of the residual will be
    290:   computed and used in the convergence test of `KSPSolve()` for the given `KSP` context

    292:   Logically Collective

    294:   Input Parameters:
    295: + ksp - Krylov solver context
    296: - it  - use -1 to check at all iterations

    298:   Level: advanced

    300:   Notes:
    301:   Currently only works with `KSPCG`, `KSPBCGS` and `KSPIBCGS`

    303:   Use `KSPSetNormType`(ksp,`KSP_NORM_NONE`) to never check the norm

    305:   On steps where the norm is not computed, the previous norm is still in the variable, so if you run with, for example,
    306:   `-ksp_monitor` the residual norm will appear to be unchanged for several iterations (though it is not really unchanged).

    308:   Certain methods such as `KSPGMRES` always compute the residual norm, this routine will not change that computation, but it will
    309:   prevent the computed norm from being checked.

    311: .seealso: [](ch_ksp), `KSP`, `KSPSetUp()`, `KSPSolve()`, `KSPDestroy()`, `KSPConvergedSkip()`, `KSPSetNormType()`, `KSPSetLagNorm()`
    312: @*/
    313: PetscErrorCode KSPSetCheckNormIteration(KSP ksp, PetscInt it)
    314: {
    315:   PetscFunctionBegin;
    318:   ksp->chknorm = it;
    319:   PetscFunctionReturn(PETSC_SUCCESS);
    320: }

    322: /*@
    323:   KSPSetLagNorm - Lags the residual norm calculation so that it is computed as part of the `MPI_Allreduce()` used for
    324:   computing the inner products needed for the next iteration.

    326:   Logically Collective

    328:   Input Parameters:
    329: + ksp - Krylov solver context
    330: - flg - `PETSC_TRUE` or `PETSC_FALSE`

    332:   Options Database Key:
    333: . -ksp_lag_norm - lag the calculated residual norm

    335:   Level: advanced

    337:   Notes:
    338:   Currently only works with `KSPIBCGS`.

    340:   This can reduce communication costs at the expense of doing
    341:   one additional iteration because the norm used in the convergence test of `KSPSolve()` is one iteration behind the actual
    342:   current residual norm (which has not yet been computed due to the lag).

    344:   Use `KSPSetNormType`(ksp,`KSP_NORM_NONE`) to never check the norm

    346:   If you lag the norm and run with, for example, `-ksp_monitor`, the residual norm reported will be the lagged one.

    348:   `KSPSetCheckNormIteration()` is an alternative way of avoiding the expense of computing the residual norm at each iteration.

    350: .seealso: [](ch_ksp), `KSPSetUp()`, `KSPSolve()`, `KSPDestroy()`, `KSPConvergedSkip()`, `KSPSetNormType()`, `KSPSetCheckNormIteration()`
    351: @*/
    352: PetscErrorCode KSPSetLagNorm(KSP ksp, PetscBool flg)
    353: {
    354:   PetscFunctionBegin;
    357:   ksp->lagnorm = flg;
    358:   PetscFunctionReturn(PETSC_SUCCESS);
    359: }

    361: /*@
    362:   KSPSetSupportedNorm - Sets a norm and preconditioner side supported by a `KSPType`

    364:   Logically Collective

    366:   Input Parameters:
    367: + ksp      - Krylov method
    368: . normtype - supported norm type of the type `KSPNormType`
    369: . pcside   - preconditioner side, of the type `PCSide` that can be used with this `KSPNormType`
    370: - priority - positive integer preference for this combination; larger values have higher priority

    372:   Level: developer

    374:   Notes:
    375:   This function should be called from the implementation files `KSPCreate_XXX()` to declare
    376:   which norms and preconditioner sides are supported. Users should not call this
    377:   function.

    379:   This function can be called multiple times for each combination of `KSPNormType` and `PCSide`
    380:   the `KSPType` supports

    382: .seealso: [](ch_ksp), `KSP`, `KSPNormType`, `PCSide`, `KSPSetNormType()`, `KSPSetPCSide()`
    383: @*/
    384: PetscErrorCode KSPSetSupportedNorm(KSP ksp, KSPNormType normtype, PCSide pcside, PetscInt priority)
    385: {
    386:   PetscFunctionBegin;
    388:   ksp->normsupporttable[normtype][pcside] = priority;
    389:   PetscFunctionReturn(PETSC_SUCCESS);
    390: }

    392: static PetscErrorCode KSPNormSupportTableReset_Private(KSP ksp)
    393: {
    394:   PetscFunctionBegin;
    395:   PetscCall(PetscMemzero(ksp->normsupporttable, sizeof(ksp->normsupporttable)));
    396:   ksp->pc_side  = ksp->pc_side_set;
    397:   ksp->normtype = ksp->normtype_set;
    398:   PetscFunctionReturn(PETSC_SUCCESS);
    399: }

    401: PetscErrorCode KSPSetUpNorms_Private(KSP ksp, PetscBool errorifnotsupported, KSPNormType *normtype, PCSide *pcside)
    402: {
    403:   PetscInt i, j, best, ibest = 0, jbest = 0;

    405:   PetscFunctionBegin;
    406:   best = 0;
    407:   for (i = 0; i < KSP_NORM_MAX; i++) {
    408:     for (j = 0; j < PC_SIDE_MAX; j++) {
    409:       if ((ksp->normtype == KSP_NORM_DEFAULT || ksp->normtype == i) && (ksp->pc_side == PC_SIDE_DEFAULT || ksp->pc_side == j) && ksp->normsupporttable[i][j] > best) {
    410:         best  = ksp->normsupporttable[i][j];
    411:         ibest = i;
    412:         jbest = j;
    413:       }
    414:     }
    415:   }
    416:   if (best < 1 && errorifnotsupported) {
    417:     PetscCheck(ksp->normtype != KSP_NORM_DEFAULT || ksp->pc_side != PC_SIDE_DEFAULT, PetscObjectComm((PetscObject)ksp), PETSC_ERR_PLIB, "The %s KSP implementation did not call KSPSetSupportedNorm()", ((PetscObject)ksp)->type_name);
    418:     PetscCheck(ksp->normtype != KSP_NORM_DEFAULT, PetscObjectComm((PetscObject)ksp), PETSC_ERR_SUP, "KSP %s does not support preconditioner side %s", ((PetscObject)ksp)->type_name, PCSides[ksp->pc_side]);
    419:     PetscCheck(ksp->pc_side != PC_SIDE_DEFAULT, PetscObjectComm((PetscObject)ksp), PETSC_ERR_SUP, "KSP %s does not support norm type %s", ((PetscObject)ksp)->type_name, KSPNormTypes[ksp->normtype]);
    420:     SETERRQ(PetscObjectComm((PetscObject)ksp), PETSC_ERR_SUP, "KSP %s does not support norm type %s with preconditioner side %s", ((PetscObject)ksp)->type_name, KSPNormTypes[ksp->normtype], PCSides[ksp->pc_side]);
    421:   }
    422:   if (normtype) *normtype = (KSPNormType)ibest;
    423:   if (pcside) *pcside = (PCSide)jbest;
    424:   PetscFunctionReturn(PETSC_SUCCESS);
    425: }

    427: /*@
    428:   KSPGetNormType - Gets the `KSPNormType` that is used for convergence testing during `KSPSolve()` for this `KSP` context

    430:   Not Collective

    432:   Input Parameter:
    433: . ksp - Krylov solver context

    435:   Output Parameter:
    436: . normtype - the `KSPNormType` that is used for convergence testing

    438:   Level: advanced

    440: .seealso: [](ch_ksp), `KSPNormType`, `KSPSetNormType()`, `KSPConvergedSkip()`
    441: @*/
    442: PetscErrorCode KSPGetNormType(KSP ksp, KSPNormType *normtype)
    443: {
    444:   PetscFunctionBegin;
    446:   PetscAssertPointer(normtype, 2);
    447:   PetscCall(KSPSetUpNorms_Private(ksp, PETSC_TRUE, &ksp->normtype, &ksp->pc_side));
    448:   *normtype = ksp->normtype;
    449:   PetscFunctionReturn(PETSC_SUCCESS);
    450: }

    452: #if defined(PETSC_HAVE_SAWS)
    453: #include <petscviewersaws.h>
    454: #endif

    456: /*@
    457:   KSPSetOperators - Sets the matrix associated with the linear system
    458:   and a (possibly) different one from which the preconditioner will be built into the `KSP` context. The matrix will then be used during `KSPSolve()`

    460:   Collective

    462:   Input Parameters:
    463: + ksp  - the `KSP` context
    464: . Amat - the matrix that defines the linear system
    465: - Pmat - the matrix to be used in constructing the preconditioner, usually the same as `Amat`.

    467:   Level: beginner

    469:   Notes:
    470: .vb
    471:   KSPSetOperators(ksp, Amat, Pmat);
    472: .ve
    473:   is the same as
    474: .vb
    475:   KSPGetPC(ksp, &pc);
    476:   PCSetOperators(pc, Amat, Pmat);
    477: .ve
    478:   and is equivalent to
    479: .vb
    480:   PCCreate(PetscObjectComm((PetscObject)ksp), &pc);
    481:   PCSetOperators(pc, Amat, Pmat);
    482:   KSPSetPC(ksp, pc);
    483: .ve

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

    488:   All future calls to `KSPSetOperators()` must use the same size matrices, unless `KSPReset()` is called!

    490:   Passing a `NULL` for `Amat` or `Pmat` removes the matrix that is currently being used from the `KSP` context.

    492:   If you wish to replace either `Amat` or `Pmat` but leave the other one untouched then
    493:   first call `KSPGetOperators()` to get the one you wish to keep, call `PetscObjectReference()`
    494:   on it and then pass it back in your call to `KSPSetOperators()`.

    496:   Developer Notes:
    497:   If the operators have NOT been set with `KSPSetOperators()` then the operators
    498:   are created in the `PC` and returned to the user. In this case, if both operators
    499:   mat and pmat are requested, two DIFFERENT operators will be returned. If
    500:   only one is requested both operators in the `PC` will be the same (i.e. as
    501:   if one had called `KSPSetOperators()` with the same argument for both `Mat`s).
    502:   The user must set the sizes of the returned matrices and their type etc just
    503:   as if the user created them with `MatCreate()`. For example,

    505: .vb
    506:          KSPGetOperators(ksp/pc,&mat,NULL); is equivalent to
    507:            set size, type, etc of mat

    509:          MatCreate(comm,&mat);
    510:          KSP/PCSetOperators(ksp/pc,mat,mat);
    511:          PetscObjectDereference((PetscObject)mat);
    512:            set size, type, etc of mat

    514:      and

    516:          KSP/PCGetOperators(ksp/pc,&mat,&pmat); is equivalent to
    517:            set size, type, etc of mat and pmat

    519:          MatCreate(comm,&mat);
    520:          MatCreate(comm,&pmat);
    521:          KSP/PCSetOperators(ksp/pc,mat,pmat);
    522:          PetscObjectDereference((PetscObject)mat);
    523:          PetscObjectDereference((PetscObject)pmat);
    524:            set size, type, etc of mat and pmat
    525: .ve

    527:   The rationale for this support is so that when creating a `TS`, `SNES`, or `KSP` the hierarchy
    528:   of underlying objects (i.e. `SNES`, `KSP`, `PC`, `Mat`) and their lifespans can be completely
    529:   managed by the top most level object (i.e. the `TS`, `SNES`, or `KSP`). Another way to look
    530:   at this is when you create a `SNES` you do not NEED to create a `KSP` and attach it to
    531:   the `SNES` object (the `SNES` object manages it for you). Similarly when you create a `KSP`
    532:   you do not need to attach a `PC` to it (the `KSP` object manages the `PC` object for you).
    533:   Thus, why should YOU have to create the `Mat` and attach it to the `SNES`/`KSP`/`PC`, when
    534:   it can be created for you?

    536: .seealso: [](ch_ksp), `KSP`, `Mat`, `KSPSolve()`, `KSPGetPC()`, `PCGetOperators()`, `PCSetOperators()`, `KSPGetOperators()`, `KSPSetComputeOperators()`, `KSPSetComputeInitialGuess()`, `KSPSetComputeRHS()`
    537: @*/
    538: PetscErrorCode KSPSetOperators(KSP ksp, Mat Amat, Mat Pmat)
    539: {
    540:   PetscFunctionBegin;
    544:   if (Amat) PetscCheckSameComm(ksp, 1, Amat, 2);
    545:   if (Pmat) PetscCheckSameComm(ksp, 1, Pmat, 3);
    546:   if (!ksp->pc) PetscCall(KSPGetPC(ksp, &ksp->pc));
    547:   PetscCall(PCSetOperators(ksp->pc, Amat, Pmat));
    548:   if (ksp->setupstage == KSP_SETUP_NEWRHS) ksp->setupstage = KSP_SETUP_NEWMATRIX; /* so that next solve call will call PCSetUp() on new matrix */
    549:   PetscFunctionReturn(PETSC_SUCCESS);
    550: }

    552: /*@
    553:   KSPGetOperators - Gets the matrix associated with the linear system
    554:   and a (possibly) different one used to construct the preconditioner from the `KSP` context

    556:   Collective

    558:   Input Parameter:
    559: . ksp - the `KSP` context

    561:   Output Parameters:
    562: + Amat - the matrix that defines the linear system
    563: - Pmat - the matrix to be used in constructing the preconditioner, usually the same as `Amat`.

    565:   Level: intermediate

    567:   Notes:
    568:   If `KSPSetOperators()` has not been called then the `KSP` object will attempt to automatically create the matrix `Amat` and return it

    570:   Use `KSPGetOperatorsSet()` to determine if matrices have been provided.

    572:   DOES NOT increase the reference counts of the matrix, so you should NOT destroy them.

    574: .seealso: [](ch_ksp), `KSP`, `KSPSolve()`, `KSPGetPC()`, `PCSetOperators()`, `KSPSetOperators()`, `KSPGetOperatorsSet()`
    575: @*/
    576: PetscErrorCode KSPGetOperators(KSP ksp, Mat *Amat, Mat *Pmat)
    577: {
    578:   PetscFunctionBegin;
    580:   if (!ksp->pc) PetscCall(KSPGetPC(ksp, &ksp->pc));
    581:   PetscCall(PCGetOperators(ksp->pc, Amat, Pmat));
    582:   PetscFunctionReturn(PETSC_SUCCESS);
    583: }

    585: /*@
    586:   KSPGetOperatorsSet - Determines if the matrix associated with the linear system and
    587:   possibly a different one from which the preconditioner will be built have been set in the `KSP` with `KSPSetOperators()`

    589:   Not Collective, though the results on all processes will be the same

    591:   Input Parameter:
    592: . ksp - the `KSP` context

    594:   Output Parameters:
    595: + mat  - the matrix associated with the linear system was set
    596: - pmat - matrix from which the preconditioner will be built, usually the same as `mat` was set

    598:   Level: intermediate

    600:   Note:
    601:   This routine exists because if you call `KSPGetOperators()` on a `KSP` that does not yet have operators they are
    602:   automatically created in the call.

    604: .seealso: [](ch_ksp), `KSP`, `PCSetOperators()`, `KSPGetOperators()`, `KSPSetOperators()`, `PCGetOperators()`, `PCGetOperatorsSet()`
    605: @*/
    606: PetscErrorCode KSPGetOperatorsSet(KSP ksp, PetscBool *mat, PetscBool *pmat)
    607: {
    608:   PetscFunctionBegin;
    610:   if (!ksp->pc) PetscCall(KSPGetPC(ksp, &ksp->pc));
    611:   PetscCall(PCGetOperatorsSet(ksp->pc, mat, pmat));
    612:   PetscFunctionReturn(PETSC_SUCCESS);
    613: }

    615: /*@C
    616:   KSPSetPreSolve - Sets a function that is called at the beginning of each `KSPSolve()`. Used in conjunction with `KSPSetPostSolve()`.

    618:   Logically Collective

    620:   Input Parameters:
    621: + ksp      - the solver object
    622: . presolve - the function to call before the solve, see` KSPPSolveFn`
    623: - ctx      - an optional context needed by the function

    625:   Level: developer

    627:   Notes:
    628:   The function provided here `presolve` is used to modify the right hand side, and possibly the matrix, of the linear system to be solved.
    629:   The function provided with `KSPSetPostSolve()` then modifies the resulting solution of that linear system to obtain the correct solution
    630:   to the initial linear system.

    632:   The functions `PCPreSolve()` and `PCPostSolve()` provide a similar functionality and are used, for example with `PCEISENSTAT`.

    634: .seealso: [](ch_ksp), `KSPPSolveFn`, `KSPSetUp()`, `KSPSolve()`, `KSPDestroy()`, `KSP`, `KSPSetPostSolve()`, `PCEISENSTAT`, `PCPreSolve()`, `PCPostSolve()`
    635: @*/
    636: PetscErrorCode KSPSetPreSolve(KSP ksp, KSPPSolveFn *presolve, void *ctx)
    637: {
    638:   PetscFunctionBegin;
    640:   ksp->presolve = presolve;
    641:   ksp->prectx   = ctx;
    642:   PetscFunctionReturn(PETSC_SUCCESS);
    643: }

    645: /*@C
    646:   KSPSetPostSolve - Sets a function that is called at the end of each `KSPSolve()` (whether it converges or not). Used in conjunction with `KSPSetPreSolve()`.

    648:   Logically Collective

    650:   Input Parameters:
    651: + ksp       - the solver object
    652: . postsolve - the function to call after the solve, see` KSPPSolveFn`
    653: - ctx       - an optional context needed by the function

    655:   Level: developer

    657: .seealso: [](ch_ksp), `KSPPSolveFn`, `KSPSetUp()`, `KSPSolve()`, `KSPDestroy()`, `KSP`, `KSPSetPreSolve()`, `PCEISENSTAT`
    658: @*/
    659: PetscErrorCode KSPSetPostSolve(KSP ksp, KSPPSolveFn *postsolve, void *ctx)
    660: {
    661:   PetscFunctionBegin;
    663:   ksp->postsolve = postsolve;
    664:   ksp->postctx   = ctx;
    665:   PetscFunctionReturn(PETSC_SUCCESS);
    666: }

    668: /*@
    669:   KSPSetNestLevel - sets the amount of nesting the `KSP` has. That is the number of levels of `KSP` above this `KSP` in a linear solve.

    671:   Collective

    673:   Input Parameters:
    674: + ksp   - the `KSP`
    675: - level - the nest level

    677:   Level: developer

    679:   Note:
    680:   For example, the `KSP` in each block of a `KSPBJACOBI` has a level of 1, while the outer `KSP` has a level of 0.

    682: .seealso: [](ch_ksp), `KSPSetUp()`, `KSPSolve()`, `KSPDestroy()`, `KSP`, `KSPGMRES`, `KSPType`, `KSPGetNestLevel()`, `PCSetKSPNestLevel()`, `PCGetKSPNestLevel()`
    683: @*/
    684: PetscErrorCode KSPSetNestLevel(KSP ksp, PetscInt level)
    685: {
    686:   PetscFunctionBegin;
    689:   ksp->nestlevel = level;
    690:   PetscFunctionReturn(PETSC_SUCCESS);
    691: }

    693: /*@
    694:   KSPGetNestLevel - gets the amount of nesting the `KSP` has

    696:   Not Collective

    698:   Input Parameter:
    699: . ksp - the `KSP`

    701:   Output Parameter:
    702: . level - the nest level

    704:   Level: developer

    706: .seealso: [](ch_ksp), `KSPSetUp()`, `KSPSolve()`, `KSPDestroy()`, `KSP`, `KSPGMRES`, `KSPType`, `KSPSetNestLevel()`, `PCSetKSPNestLevel()`, `PCGetKSPNestLevel()`
    707: @*/
    708: PetscErrorCode KSPGetNestLevel(KSP ksp, PetscInt *level)
    709: {
    710:   PetscFunctionBegin;
    712:   PetscAssertPointer(level, 2);
    713:   *level = ksp->nestlevel;
    714:   PetscFunctionReturn(PETSC_SUCCESS);
    715: }

    717: /*@
    718:   KSPCreate - Creates the `KSP` context. This `KSP` context is used in PETSc to solve linear systems with `KSPSolve()`

    720:   Collective

    722:   Input Parameter:
    723: . comm - MPI communicator

    725:   Output Parameter:
    726: . inksp - location to put the `KSP` context

    728:   Level: beginner

    730:   Note:
    731:   The default `KSPType` is `KSPGMRES` with a restart of 30, using modified Gram-Schmidt orthogonalization. The `KSPType` may be
    732:   changed with `KSPSetType()`

    734: .seealso: [](ch_ksp), `KSPSetUp()`, `KSPSolve()`, `KSPDestroy()`, `KSP`, `KSPGMRES`, `KSPType`, `KSPSetType()`
    735: @*/
    736: PetscErrorCode KSPCreate(MPI_Comm comm, KSP *inksp)
    737: {
    738:   KSP   ksp;
    739:   void *ctx;

    741:   PetscFunctionBegin;
    742:   PetscAssertPointer(inksp, 2);
    743:   PetscCall(KSPInitializePackage());

    745:   PetscCall(PetscHeaderCreate(ksp, KSP_CLASSID, "KSP", "Krylov Method", "KSP", comm, KSPDestroy, KSPView));
    746:   ksp->default_max_it = ksp->max_it = 10000;
    747:   ksp->pc_side = ksp->pc_side_set = PC_SIDE_DEFAULT;

    749:   ksp->default_rtol = ksp->rtol = 1.e-5;
    750:   ksp->default_abstol = ksp->abstol = PetscDefined(USE_REAL_SINGLE) ? 1.e-25 : 1.e-50;
    751:   ksp->default_divtol = ksp->divtol = 1.e4;

    753:   ksp->chknorm  = -1;
    754:   ksp->normtype = ksp->normtype_set = KSP_NORM_DEFAULT;
    755:   ksp->rnorm                        = 0.0;
    756:   ksp->its                          = 0;
    757:   ksp->guess_zero                   = PETSC_TRUE;
    758:   ksp->calc_sings                   = PETSC_FALSE;
    759:   ksp->res_hist                     = NULL;
    760:   ksp->res_hist_alloc               = NULL;
    761:   ksp->res_hist_len                 = 0;
    762:   ksp->res_hist_max                 = 0;
    763:   ksp->res_hist_reset               = PETSC_TRUE;
    764:   ksp->err_hist                     = NULL;
    765:   ksp->err_hist_alloc               = NULL;
    766:   ksp->err_hist_len                 = 0;
    767:   ksp->err_hist_max                 = 0;
    768:   ksp->err_hist_reset               = PETSC_TRUE;
    769:   ksp->numbermonitors               = 0;
    770:   ksp->numberreasonviews            = 0;
    771:   ksp->setfromoptionscalled         = 0;
    772:   ksp->nmax                         = PETSC_DECIDE;

    774:   PetscCall(KSPConvergedDefaultCreate(&ctx));
    775:   PetscCall(KSPSetConvergenceTest(ksp, KSPConvergedDefault, ctx, KSPConvergedDefaultDestroy));
    776:   ksp->ops->buildsolution = KSPBuildSolutionDefault;
    777:   ksp->ops->buildresidual = KSPBuildResidualDefault;

    779:   ksp->vec_sol    = NULL;
    780:   ksp->vec_rhs    = NULL;
    781:   ksp->pc         = NULL;
    782:   ksp->data       = NULL;
    783:   ksp->nwork      = 0;
    784:   ksp->work       = NULL;
    785:   ksp->reason     = KSP_CONVERGED_ITERATING;
    786:   ksp->setupstage = KSP_SETUP_NEW;

    788:   PetscCall(KSPNormSupportTableReset_Private(ksp));

    790:   *inksp = ksp;
    791:   PetscFunctionReturn(PETSC_SUCCESS);
    792: }

    794: /*@
    795:   KSPSetType - Sets the algorithm/method to be used to solve the linear system with the given `KSP`

    797:   Logically Collective

    799:   Input Parameters:
    800: + ksp  - the Krylov space context
    801: - type - a known method

    803:   Options Database Key:
    804: . -ksp_type  <method> - Sets the method; see `KSPType` or use `-help` for a list  of available methods (for instance, cg or gmres)

    806:   Level: intermediate

    808:   Notes:
    809:   See `KSPType` for available methods (for instance, `KSPCG` or `KSPGMRES`).

    811:   Normally, it is best to use the `KSPSetFromOptions()` command and
    812:   then set the `KSP` type from the options database rather than by using
    813:   this routine.  Using the options database provides the user with
    814:   maximum flexibility in evaluating the many different Krylov methods.
    815:   The `KSPSetType()` routine is provided for those situations where it
    816:   is necessary to set the iterative solver independently of the command
    817:   line or options database.  This might be the case, for example, when
    818:   the choice of iterative solver changes during the execution of the
    819:   program, and the user's application is taking responsibility for
    820:   choosing the appropriate method.  In other words, this routine is
    821:   not for beginners.

    823:   Developer Note:
    824:   `KSPRegister()` is used to add Krylov types to `KSPList` from which they are accessed by `KSPSetType()`.

    826: .seealso: [](ch_ksp), `PCSetType()`, `KSPType`, `KSPRegister()`, `KSPCreate()`, `KSP`
    827: @*/
    828: PetscErrorCode KSPSetType(KSP ksp, KSPType type)
    829: {
    830:   PetscBool match;
    831:   PetscErrorCode (*r)(KSP);

    833:   PetscFunctionBegin;
    835:   PetscAssertPointer(type, 2);

    837:   PetscCall(PetscObjectTypeCompare((PetscObject)ksp, type, &match));
    838:   if (match) PetscFunctionReturn(PETSC_SUCCESS);

    840:   PetscCall(PetscFunctionListFind(KSPList, type, &r));
    841:   PetscCheck(r, PetscObjectComm((PetscObject)ksp), PETSC_ERR_ARG_UNKNOWN_TYPE, "Unable to find requested KSP type %s", type);
    842:   /* Destroy the previous private KSP context */
    843:   PetscTryTypeMethod(ksp, destroy);

    845:   /* Reinitialize function pointers in KSPOps structure */
    846:   PetscCall(PetscMemzero(ksp->ops, sizeof(struct _KSPOps)));
    847:   ksp->ops->buildsolution = KSPBuildSolutionDefault;
    848:   ksp->ops->buildresidual = KSPBuildResidualDefault;
    849:   PetscCall(KSPNormSupportTableReset_Private(ksp));
    850:   ksp->converged_neg_curve = PETSC_FALSE; // restore default
    851:   ksp->setupnewmatrix      = PETSC_FALSE; // restore default (setup not called in case of new matrix)
    852:   /* Call the KSPCreate_XXX routine for this particular Krylov solver */
    853:   ksp->setupstage     = KSP_SETUP_NEW;
    854:   ksp->guess_not_read = PETSC_FALSE; // restore default
    855:   PetscCall((*r)(ksp));
    856:   PetscCall(PetscObjectChangeTypeName((PetscObject)ksp, type));
    857:   PetscFunctionReturn(PETSC_SUCCESS);
    858: }

    860: /*@
    861:   KSPGetType - Gets the `KSP` type as a string from the `KSP` object.

    863:   Not Collective

    865:   Input Parameter:
    866: . ksp - Krylov context

    868:   Output Parameter:
    869: . type - name of the `KSP` method

    871:   Level: intermediate

    873: .seealso: [](ch_ksp), `KSPType`, `KSP`, `KSPSetType()`
    874: @*/
    875: PetscErrorCode KSPGetType(KSP ksp, KSPType *type)
    876: {
    877:   PetscFunctionBegin;
    879:   PetscAssertPointer(type, 2);
    880:   *type = ((PetscObject)ksp)->type_name;
    881:   PetscFunctionReturn(PETSC_SUCCESS);
    882: }

    884: /*@C
    885:   KSPRegister -  Adds a method, `KSPType`, to the Krylov subspace solver package.

    887:   Not Collective, No Fortran Support

    889:   Input Parameters:
    890: + sname    - name of a new user-defined solver
    891: - function - routine to create method

    893:   Level: advanced

    895:   Note:
    896:   `KSPRegister()` may be called multiple times to add several user-defined solvers.

    898:   Example Usage:
    899: .vb
    900:    KSPRegister("my_solver", MySolverCreate);
    901: .ve

    903:   Then, your solver can be chosen with the procedural interface via
    904: .vb
    905:   KSPSetType(ksp, "my_solver")
    906: .ve
    907:   or at runtime via the option `-ksp_type my_solver`

    909: .seealso: [](ch_ksp), `KSP`, `KSPType`, `KSPSetType`, `KSPRegisterAll()`
    910: @*/
    911: PetscErrorCode KSPRegister(const char sname[], PetscErrorCode (*function)(KSP))
    912: {
    913:   PetscFunctionBegin;
    914:   PetscCall(KSPInitializePackage());
    915:   PetscCall(PetscFunctionListAdd(&KSPList, sname, function));
    916:   PetscFunctionReturn(PETSC_SUCCESS);
    917: }

    919: PetscErrorCode KSPMonitorMakeKey_Internal(const char name[], PetscViewerType vtype, PetscViewerFormat format, char key[])
    920: {
    921:   PetscFunctionBegin;
    922:   PetscCall(PetscStrncpy(key, name, PETSC_MAX_PATH_LEN));
    923:   PetscCall(PetscStrlcat(key, ":", PETSC_MAX_PATH_LEN));
    924:   PetscCall(PetscStrlcat(key, vtype, PETSC_MAX_PATH_LEN));
    925:   PetscCall(PetscStrlcat(key, ":", PETSC_MAX_PATH_LEN));
    926:   PetscCall(PetscStrlcat(key, PetscViewerFormats[format], PETSC_MAX_PATH_LEN));
    927:   PetscFunctionReturn(PETSC_SUCCESS);
    928: }

    930: /*@C
    931:   KSPMonitorRegister -  Registers a Krylov subspace solver monitor routine that may be accessed with `KSPMonitorSetFromOptions()`

    933:   Not Collective

    935:   Input Parameters:
    936: + name    - name of a new monitor type
    937: . vtype   - A `PetscViewerType` for the output
    938: . format  - A `PetscViewerFormat` for the output
    939: . monitor - Monitor routine, see `KSPMonitorRegisterFn`
    940: . create  - Creation routine, or `NULL`
    941: - destroy - Destruction routine, or `NULL`

    943:   Level: advanced

    945:   Notes:
    946:   `KSPMonitorRegister()` may be called multiple times to add several user-defined monitors.

    948:   The calling sequence for the given function matches the calling sequence used by `KSPMonitorFn` functions passed to `KSPMonitorSet()` with the additional
    949:   requirement that its final argument be a `PetscViewerAndFormat`.

    951:   Example Usage:
    952: .vb
    953:   KSPMonitorRegister("my_monitor", PETSCVIEWERASCII, PETSC_VIEWER_ASCII_INFO_DETAIL, MyMonitor, NULL, NULL);
    954: .ve

    956:   Then, your monitor can be chosen with the procedural interface via
    957: .vb
    958:   KSPMonitorSetFromOptions(ksp, "-ksp_monitor_my_monitor", "my_monitor", NULL)
    959: .ve
    960:   or at runtime via the option `-ksp_monitor_my_monitor`

    962: .seealso: [](ch_ksp), `KSP`, `KSPMonitorSet()`, `KSPMonitorRegisterAll()`, `KSPMonitorSetFromOptions()`
    963: @*/
    964: PetscErrorCode KSPMonitorRegister(const char name[], PetscViewerType vtype, PetscViewerFormat format, KSPMonitorRegisterFn *monitor, KSPMonitorRegisterCreateFn *create, KSPMonitorRegisterDestroyFn *destroy)
    965: {
    966:   char key[PETSC_MAX_PATH_LEN];

    968:   PetscFunctionBegin;
    969:   PetscCall(KSPInitializePackage());
    970:   PetscCall(KSPMonitorMakeKey_Internal(name, vtype, format, key));
    971:   PetscCall(PetscFunctionListAdd(&KSPMonitorList, key, monitor));
    972:   if (create) PetscCall(PetscFunctionListAdd(&KSPMonitorCreateList, key, create));
    973:   if (destroy) PetscCall(PetscFunctionListAdd(&KSPMonitorDestroyList, key, destroy));
    974:   PetscFunctionReturn(PETSC_SUCCESS);
    975: }