Date: 2026-03-01T05:24:50+00:00

Actual source code: ex36.cxx

      1: /*
      2: Inhomogeneous Laplacian in 3-D. Modeled by the partial differential equation

      4:    -div \rho grad u + \alpha u = f,  0 < x,y,z < 1,

      6: Problem 1: (Default)

      8:   Use the following exact solution with Dirichlet boundary condition

     10:     u = sin(pi*x)*sin(pi*y)*sin(pi*z)

     12:   with Dirichlet boundary conditions

     14:      u = f(x,y,z) for x = 0, x = 1, y = 0, y = 1, z = 0, z = 1

     16:   and \rho = 1.0, \alpha = 10.0 uniformly in the domain.

     18:   Use an appropriate forcing function to measure convergence.

     20: Usage:

     22:   Measure convergence rate with uniform refinement with the options: "-problem 1 -error".

     24:     mpiexec -n $NP ./ex36 -problem 1 -error -n 4 -levels 5 -pc_type gamg
     25:     mpiexec -n $NP ./ex36 -problem 1 -error -n 8 -levels 4 -pc_type gamg
     26:     mpiexec -n $NP ./ex36 -problem 1 -error -n 16 -levels 3 -pc_type mg
     27:     mpiexec -n $NP ./ex36 -problem 1 -error -n 32 -levels 2 -pc_type mg
     28:     mpiexec -n $NP ./ex36 -problem 1 -error -n 64 -levels 1 -mg
     29:     mpiexec -n $NP ./ex36 -problem 1 -error -n 128 -levels 0 -mg

     31:   Or with an external mesh file representing [0, 1]^3,

     33:     mpiexec -n $NP ./ex36 -problem 1 -file ./external_mesh.h5m -levels 2 -error -pc_type mg

     35: Problem 2:

     37:   Use the forcing function

     39:      f = e^{-((x-xr)^2+(y-yr)^2+(z-zr)^2)/\nu}

     41:   with Dirichlet boundary conditions

     43:      u = f(x,y,z) for x = 0, x = 1, y = 0, y = 1, z = 0, z = 1

     45:   or pure Neumman boundary conditions

     47: Usage:

     49:   Run with different values of \rho and \nu (problem 1) to control diffusion and gaussian source spread. This uses the internal mesh generator implemented in DMMoab.

     51:     mpiexec -n $NP ./ex36 -problem 2 -n 20 -nu 0.02 -rho 0.01
     52:     mpiexec -n $NP ./ex36 -problem 2 -n 40 -nu 0.01 -rho 0.005 -io -ksp_monitor
     53:     mpiexec -n $NP ./ex36 -problem 2 -n 80 -nu 0.01 -rho 0.005 -io -ksp_monitor -pc_type gamg
     54:     mpiexec -n $NP ./ex36 -problem 2 -n 160 -bc neumann -nu 0.005 -rho 0.01 -io
     55:     mpiexec -n $NP ./ex36 -problem 2 -n 320 -bc neumann -nu 0.001 -rho 1 -io

     57:   Or with an external mesh file representing [0, 1]^3,

     59:     mpiexec -n $NP ./ex36 -problem 2 -file ./external_mesh.h5m -levels 1 -pc_type gamg

     61: */

     63: static char help[] = "\
     64:                       Solves a three dimensional inhomogeneous Laplacian equation with a Gaussian source.\n \
     65:                       Usage: ./ex36 -bc dirichlet -nu .01 -n 10\n";

     67: /* PETSc includes */
     68: #include <petscksp.h>
     69: #include <petscdmmoab.h>

     71: typedef enum {
     72:   DIRICHLET,
     73:   NEUMANN
     74: } BCType;

     76: typedef struct {
     77:   PetscInt  problem, dim, n, nlevels;
     78:   PetscReal rho;
     79:   PetscReal bounds[6];
     80:   PetscReal xyzref[3];
     81:   PetscReal nu;
     82:   BCType    bcType;
     83:   char      filename[PETSC_MAX_PATH_LEN];
     84:   PetscBool use_extfile, io, error, usetet, usemg;

     86:   /* Discretization parameters */
     87:   int VPERE;
     88: } UserContext;

     90: static PetscErrorCode ComputeMatrix_MOAB(KSP, Mat, Mat, void *);
     91: static PetscErrorCode ComputeRHS_MOAB(KSP, Vec, void *);
     92: static PetscErrorCode ComputeDiscreteL2Error(KSP ksp, Vec err, UserContext *user);
     93: static PetscErrorCode InitializeOptions(UserContext *user);

     95: int main(int argc, char **argv)
     96: {
     97:   const char *fields[1] = {"T-Variable"};
     98:   DM          dm, dmref, *dmhierarchy;
     99:   UserContext user;
    100:   PetscInt    k;
    101:   KSP         ksp;
    102:   PC          pc;
    103:   Vec         errv;
    104:   Mat         R;
    105:   Vec         b, x;

    107:   PetscFunctionBeginUser;
    108:   PetscCall(PetscInitialize(&argc, &argv, nullptr, help));

    110:   PetscCall(InitializeOptions(&user));

    112:   /* Create the DM object from either a mesh file or from in-memory structured grid */
    113:   if (user.use_extfile) {
    114:     PetscCall(DMMoabLoadFromFile(PETSC_COMM_WORLD, user.dim, 1, user.filename, "", &dm));
    115:   } else {
    116:     PetscCall(DMMoabCreateBoxMesh(PETSC_COMM_WORLD, user.dim, user.usetet, NULL, user.n, 1, &dm));
    117:   }
    118:   PetscCall(DMSetFromOptions(dm));
    119:   PetscCall(DMMoabSetFieldNames(dm, 1, fields));

    121:   /* SetUp the data structures for DMMOAB */
    122:   PetscCall(DMSetUp(dm));

    124:   PetscCall(DMSetApplicationContext(dm, &user));

    126:   PetscCall(KSPCreate(PETSC_COMM_WORLD, &ksp));
    127:   PetscCall(KSPSetComputeRHS(ksp, ComputeRHS_MOAB, &user));
    128:   PetscCall(KSPSetComputeOperators(ksp, ComputeMatrix_MOAB, &user));

    130:   if (user.nlevels) {
    131:     PetscCall(KSPGetPC(ksp, &pc));
    132:     PetscCall(PetscMalloc(sizeof(DM) * (user.nlevels + 1), &dmhierarchy));
    133:     for (k = 0; k <= user.nlevels; k++) dmhierarchy[k] = NULL;

    135:     PetscCall(PetscPrintf(PETSC_COMM_WORLD, "Number of mesh hierarchy levels: %d\n", user.nlevels));
    136:     PetscCall(DMMoabGenerateHierarchy(dm, user.nlevels, NULL));

    138:     // coarsest grid = 0
    139:     // finest grid = nlevels
    140:     dmhierarchy[0]         = dm;
    141:     PetscBool usehierarchy = PETSC_FALSE;
    142:     if (usehierarchy) {
    143:       PetscCall(DMRefineHierarchy(dm, user.nlevels, &dmhierarchy[1]));
    144:     } else {
    145:       for (k = 1; k <= user.nlevels; k++) PetscCall(DMRefine(dmhierarchy[k - 1], MPI_COMM_NULL, &dmhierarchy[k]));
    146:     }
    147:     dmref = dmhierarchy[user.nlevels];
    148:     PetscCall(PetscObjectReference((PetscObject)dmref));

    150:     if (user.usemg) {
    151:       PetscCall(PCSetType(pc, PCMG));
    152:       PetscCall(PCMGSetLevels(pc, user.nlevels + 1, NULL));
    153:       PetscCall(PCMGSetType(pc, PC_MG_MULTIPLICATIVE));
    154:       PetscCall(PCMGSetGalerkin(pc, PC_MG_GALERKIN_BOTH));
    155:       PetscCall(PCMGSetCycleType(pc, PC_MG_CYCLE_V));
    156:       PetscCall(PCMGSetNumberSmooth(pc, 2));

    158:       for (k = 1; k <= user.nlevels; k++) {
    159:         PetscCall(DMCreateInterpolation(dmhierarchy[k - 1], dmhierarchy[k], &R, NULL));
    160:         PetscCall(PCMGSetInterpolation(pc, k, R));
    161:         PetscCall(MatDestroy(&R));
    162:       }
    163:     }

    165:     for (k = 1; k <= user.nlevels; k++) PetscCall(DMDestroy(&dmhierarchy[k]));
    166:     PetscCall(PetscFree(dmhierarchy));
    167:   } else {
    168:     dmref = dm;
    169:     PetscCall(PetscObjectReference((PetscObject)dm));
    170:   }

    172:   PetscCall(KSPSetDM(ksp, dmref));
    173:   PetscCall(KSPSetFromOptions(ksp));

    175:   /* Perform the actual solve */
    176:   PetscCall(KSPSolve(ksp, NULL, NULL));
    177:   PetscCall(KSPGetSolution(ksp, &x));
    178:   PetscCall(KSPGetRhs(ksp, &b));

    180:   if (user.error) {
    181:     PetscCall(VecDuplicate(b, &errv));
    182:     PetscCall(ComputeDiscreteL2Error(ksp, errv, &user));
    183:     PetscCall(VecDestroy(&errv));
    184:   }

    186:   if (user.io) {
    187:     /* Write out the solution along with the mesh */
    188:     PetscCall(DMMoabSetGlobalFieldVector(dmref, x));
    189: #ifdef MOAB_HAVE_HDF5
    190:     PetscCall(DMMoabOutput(dmref, "ex36.h5m", ""));
    191: #else
    192:     /* MOAB does not support true parallel writers that aren't HDF5 based
    193:        And so if you are using VTK as the output format in parallel,
    194:        the data could be jumbled due to the order in which the processors
    195:        write out their parts of the mesh and solution tags
    196:     */
    197:     PetscCall(DMMoabOutput(dmref, "ex36.vtk", ""));
    198: #endif
    199:   }

    201:   /* Cleanup objects */
    202:   PetscCall(KSPDestroy(&ksp));
    203:   PetscCall(DMDestroy(&dmref));
    204:   PetscCall(DMDestroy(&dm));
    205:   PetscCall(PetscFinalize());
    206:   return 0;
    207: }

    209: PetscReal ComputeDiffusionCoefficient(PetscReal coords[3], UserContext *user)
    210: {
    211:   if (user->problem == 2) {
    212:     if ((coords[0] > 1.0 / 3.0) && (coords[0] < 2.0 / 3.0) && (coords[1] > 1.0 / 3.0) && (coords[1] < 2.0 / 3.0) && (coords[2] > 1.0 / 3.0) && (coords[2] < 2.0 / 3.0)) return user->rho;
    213:     else return 1.0;
    214:   } else return 1.0; /* problem = 1 */
    215: }

    217: PetscReal ComputeReactionCoefficient(PetscReal coords[3], UserContext *user)
    218: {
    219:   if (user->problem == 2) {
    220:     if ((coords[0] > 1.0 / 3.0) && (coords[0] < 2.0 / 3.0) && (coords[1] > 1.0 / 3.0) && (coords[1] < 2.0 / 3.0) && (coords[2] > 1.0 / 3.0) && (coords[2] < 2.0 / 3.0)) return 10.0;
    221:     else return 0.0;
    222:   } else return 5.0; /* problem = 1 */
    223: }

    225: double ExactSolution(PetscReal coords[3], UserContext *user)
    226: {
    227:   if (user->problem == 2) {
    228:     const PetscScalar xx = (coords[0] - user->xyzref[0]) * (coords[0] - user->xyzref[0]);
    229:     const PetscScalar yy = (coords[1] - user->xyzref[1]) * (coords[1] - user->xyzref[1]);
    230:     const PetscScalar zz = (coords[2] - user->xyzref[2]) * (coords[2] - user->xyzref[2]);
    231:     return PetscExpScalar(-(xx + yy + zz) / user->nu);
    232:   } else return sin(PETSC_PI * coords[0]) * sin(PETSC_PI * coords[1]) * sin(PETSC_PI * coords[2]);
    233: }

    235: PetscReal exact_solution(PetscReal x, PetscReal y, PetscReal z)
    236: {
    237:   PetscReal coords[3] = {x, y, z};
    238:   return ExactSolution(coords, 0);
    239: }

    241: double ForcingFunction(PetscReal coords[3], UserContext *user)
    242: {
    243:   const PetscReal exact = ExactSolution(coords, user);
    244:   if (user->problem == 2) {
    245:     const PetscReal duxyz = ((coords[0] - user->xyzref[0]) + (coords[1] - user->xyzref[1]) + (coords[2] - user->xyzref[2]));
    246:     return (4.0 / user->nu * duxyz * duxyz - 6.0) * exact / user->nu;
    247:   } else {
    248:     const PetscReal reac = ComputeReactionCoefficient(coords, user);
    249:     return (3.0 * PETSC_PI * PETSC_PI + reac) * exact;
    250:   }
    251: }

    253: PetscErrorCode ComputeRHS_MOAB(KSP ksp, Vec b, void *ptr)
    254: {
    255:   UserContext              *user = (UserContext *)ptr;
    256:   DM                        dm;
    257:   PetscInt                  dof_indices[8], nc, npoints;
    258:   PetscBool                 dbdry[8];
    259:   PetscReal                 vpos[8 * 3];
    260:   PetscInt                  i, q, nconn;
    261:   const moab::EntityHandle *connect;
    262:   const moab::Range        *elocal;
    263:   moab::Interface          *mbImpl;
    264:   PetscScalar               localv[8];
    265:   PetscReal                *phi, *phypts, *jxw;
    266:   PetscBool                 elem_on_boundary;
    267:   PetscQuadrature           quadratureObj;

    269:   PetscFunctionBegin;
    270:   PetscCall(KSPGetDM(ksp, &dm));

    272:   /* reset the RHS */
    273:   PetscCall(VecSet(b, 0.0));

    275:   PetscCall(DMMoabFEMCreateQuadratureDefault(user->dim, user->VPERE, &quadratureObj));
    276:   PetscCall(PetscQuadratureGetData(quadratureObj, NULL, &nc, &npoints, NULL, NULL));
    277:   PetscCall(PetscMalloc3(user->VPERE * npoints, &phi, npoints * 3, &phypts, npoints, &jxw));

    279:   /* get the essential MOAB mesh related quantities needed for FEM assembly */
    280:   PetscCall(DMMoabGetInterface(dm, &mbImpl));
    281:   PetscCall(DMMoabGetLocalElements(dm, &elocal));

    283:   /* loop over local elements */
    284:   for (moab::Range::iterator iter = elocal->begin(); iter != elocal->end(); iter++) {
    285:     const moab::EntityHandle ehandle = *iter;

    287:     /* Get connectivity information: */
    288:     PetscCall(DMMoabGetElementConnectivity(dm, ehandle, &nconn, &connect));
    289:     PetscCheck(nconn == 4 || nconn == 8, PETSC_COMM_WORLD, PETSC_ERR_ARG_WRONG, "Only HEX8/TET4 element bases are supported in the current example. n(Connectivity)=%" PetscInt_FMT ".", nconn);

    291:     /* get the coordinates of the element vertices */
    292:     PetscCall(DMMoabGetVertexCoordinates(dm, nconn, connect, vpos));

    294:     /* get the local DoF numbers to appropriately set the element contribution in the operator */
    295:     PetscCall(DMMoabGetFieldDofsLocal(dm, nconn, connect, 0, dof_indices));

    297:     /* compute the quadrature points transformed to the physical space and then
    298:        compute the basis functions to compute local operators */
    299:     PetscCall(DMMoabFEMComputeBasis(user->dim, nconn, vpos, quadratureObj, phypts, jxw, phi, NULL));

    301:     PetscCall(PetscArrayzero(localv, nconn));
    302:     /* Compute function over the locally owned part of the grid */
    303:     for (q = 0; q < npoints; ++q) {
    304:       const double   ff     = ForcingFunction(&phypts[3 * q], user);
    305:       const PetscInt offset = q * nconn;

    307:       for (i = 0; i < nconn; ++i) localv[i] += jxw[q] * phi[offset + i] * ff;
    308:     }

    310:     /* check if element is on the boundary */
    311:     PetscCall(DMMoabIsEntityOnBoundary(dm, ehandle, &elem_on_boundary));

    313:     /* apply dirichlet boundary conditions */
    314:     if (elem_on_boundary && user->bcType == DIRICHLET) {
    315:       /* get the list of nodes on boundary so that we can enforce dirichlet conditions strongly */
    316:       PetscCall(DMMoabCheckBoundaryVertices(dm, nconn, connect, dbdry));

    318:       for (i = 0; i < nconn; ++i) {
    319:         if (dbdry[i]) { /* dirichlet node */
    320:           /* think about strongly imposing dirichlet */
    321:           localv[i] = ForcingFunction(&vpos[3 * i], user);
    322:         }
    323:       }
    324:     }

    326:     /* set the values directly into appropriate locations. Can alternately use VecSetValues */
    327:     PetscCall(VecSetValuesLocal(b, nconn, dof_indices, localv, ADD_VALUES));
    328:   }

    330:   /* force right-hand side to be consistent for singular matrix */
    331:   /* note this is really a hack, normally the model would provide you with a consistent right handside */
    332:   if (user->bcType == NEUMANN && false) {
    333:     MatNullSpace nullspace;

    335:     PetscCall(MatNullSpaceCreate(PETSC_COMM_WORLD, PETSC_TRUE, 0, 0, &nullspace));
    336:     PetscCall(MatNullSpaceRemove(nullspace, b));
    337:     PetscCall(MatNullSpaceDestroy(&nullspace));
    338:   }

    340:   /* Restore vectors */
    341:   PetscCall(VecAssemblyBegin(b));
    342:   PetscCall(VecAssemblyEnd(b));
    343:   PetscCall(PetscFree3(phi, phypts, jxw));
    344:   PetscCall(PetscQuadratureDestroy(&quadratureObj));
    345:   PetscFunctionReturn(PETSC_SUCCESS);
    346: }

    348: PetscErrorCode ComputeMatrix_MOAB(KSP ksp, Mat J, Mat jac, void *ctx)
    349: {
    350:   UserContext              *user = (UserContext *)ctx;
    351:   DM                        dm;
    352:   PetscInt                  i, j, q, nconn, nglobale, nglobalv, nc, npoints, hlevel;
    353:   PetscInt                  dof_indices[8];
    354:   PetscReal                 vpos[8 * 3], rho, alpha;
    355:   PetscBool                 dbdry[8];
    356:   const moab::EntityHandle *connect;
    357:   const moab::Range        *elocal;
    358:   moab::Interface          *mbImpl;
    359:   PetscBool                 elem_on_boundary;
    360:   PetscScalar               array[8 * 8];
    361:   PetscReal                *phi, *dphi[3], *phypts, *jxw;
    362:   PetscQuadrature           quadratureObj;

    364:   PetscFunctionBeginUser;
    365:   PetscCall(KSPGetDM(ksp, &dm));

    367:   /* get the essential MOAB mesh related quantities needed for FEM assembly */
    368:   PetscCall(DMMoabGetInterface(dm, &mbImpl));
    369:   PetscCall(DMMoabGetLocalElements(dm, &elocal));
    370:   PetscCall(DMMoabGetSize(dm, &nglobale, &nglobalv));
    371:   PetscCall(DMMoabGetHierarchyLevel(dm, &hlevel));
    372:   PetscCall(PetscPrintf(PETSC_COMM_WORLD, "ComputeMatrix: Level = %d, N(elements) = %d, N(vertices) = %d \n", hlevel, nglobale, nglobalv));

    374:   PetscCall(DMMoabFEMCreateQuadratureDefault(user->dim, user->VPERE, &quadratureObj));
    375:   PetscCall(PetscQuadratureGetData(quadratureObj, NULL, &nc, &npoints, NULL, NULL));
    376:   PetscCall(PetscMalloc6(user->VPERE * npoints, &phi, user->VPERE * npoints, &dphi[0], user->VPERE * npoints, &dphi[1], user->VPERE * npoints, &dphi[2], npoints * 3, &phypts, npoints, &jxw));

    378:   /* loop over local elements */
    379:   for (moab::Range::iterator iter = elocal->begin(); iter != elocal->end(); iter++) {
    380:     const moab::EntityHandle ehandle = *iter;

    382:     /* Get connectivity information: */
    383:     PetscCall(DMMoabGetElementConnectivity(dm, ehandle, &nconn, &connect));
    384:     PetscCheck(nconn == 4 || nconn == 8, PETSC_COMM_WORLD, PETSC_ERR_ARG_WRONG, "Only HEX8/TET4 element bases are supported in the current example. n(Connectivity)=%" PetscInt_FMT ".", nconn);

    386:     /* get the coordinates of the element vertices */
    387:     PetscCall(DMMoabGetVertexCoordinates(dm, nconn, connect, vpos));

    389:     /* get the local DoF numbers to appropriately set the element contribution in the operator */
    390:     PetscCall(DMMoabGetFieldDofsLocal(dm, nconn, connect, 0, dof_indices));

    392:     /* compute the quadrature points transformed to the physical space and
    393:        compute the basis functions and the derivatives wrt x, y and z directions */
    394:     PetscCall(DMMoabFEMComputeBasis(user->dim, nconn, vpos, quadratureObj, phypts, jxw, phi, dphi));

    396:     PetscCall(PetscArrayzero(array, nconn * nconn));

    398:     /* Compute function over the locally owned part of the grid */
    399:     for (q = 0; q < npoints; ++q) {
    400:       /* compute the inhomogeneous diffusion coefficient at the quadrature point
    401:           -- for large spatial variations, embed this property evaluation inside quadrature loop */
    402:       rho   = ComputeDiffusionCoefficient(&phypts[q * 3], user);
    403:       alpha = ComputeReactionCoefficient(&phypts[q * 3], user);

    405:       const PetscInt offset = q * nconn;

    407:       for (i = 0; i < nconn; ++i) {
    408:         for (j = 0; j < nconn; ++j) {
    409:           array[i * nconn + j] += jxw[q] * (rho * (dphi[0][offset + i] * dphi[0][offset + j] + dphi[1][offset + i] * dphi[1][offset + j] + dphi[2][offset + i] * dphi[2][offset + j]) + alpha * (phi[offset + i] * phi[offset + j]));
    410:         }
    411:       }
    412:     }

    414:     /* check if element is on the boundary */
    415:     PetscCall(DMMoabIsEntityOnBoundary(dm, ehandle, &elem_on_boundary));

    417:     /* apply dirichlet boundary conditions */
    418:     if (elem_on_boundary && user->bcType == DIRICHLET) {
    419:       /* get the list of nodes on boundary so that we can enforce dirichlet conditions strongly */
    420:       PetscCall(DMMoabCheckBoundaryVertices(dm, nconn, connect, dbdry));

    422:       for (i = 0; i < nconn; ++i) {
    423:         if (dbdry[i]) { /* dirichlet node */
    424:           /* think about strongly imposing dirichlet */
    425:           for (j = 0; j < nconn; ++j) {
    426:             /* TODO: symmetrize the system - need the RHS */
    427:             array[i * nconn + j] = 0.0;
    428:           }
    429:           array[i * nconn + i] = 1.0;
    430:         }
    431:       }
    432:     }

    434:     /* set the values directly into appropriate locations. Can alternately use VecSetValues */
    435:     PetscCall(MatSetValuesLocal(jac, nconn, dof_indices, nconn, dof_indices, array, ADD_VALUES));
    436:   }

    438:   PetscCall(MatAssemblyBegin(jac, MAT_FINAL_ASSEMBLY));
    439:   PetscCall(MatAssemblyEnd(jac, MAT_FINAL_ASSEMBLY));

    441:   if (user->bcType == NEUMANN && false) {
    442:     MatNullSpace nullspace;

    444:     PetscCall(MatNullSpaceCreate(PETSC_COMM_WORLD, PETSC_TRUE, 0, 0, &nullspace));
    445:     PetscCall(MatSetNullSpace(jac, nullspace));
    446:     PetscCall(MatNullSpaceDestroy(&nullspace));
    447:   }
    448:   PetscCall(PetscFree6(phi, dphi[0], dphi[1], dphi[2], phypts, jxw));
    449:   PetscCall(PetscQuadratureDestroy(&quadratureObj));
    450:   PetscFunctionReturn(PETSC_SUCCESS);
    451: }

    453: PetscErrorCode ComputeDiscreteL2Error(KSP ksp, Vec err, UserContext *user)
    454: {
    455:   DM                 dm;
    456:   Vec                sol;
    457:   PetscScalar        vpos[3];
    458:   const PetscScalar *x;
    459:   PetscScalar       *e;
    460:   PetscReal          l2err = 0.0, linferr = 0.0, global_l2, global_linf;
    461:   PetscInt           dof_index, N;
    462:   const moab::Range *ownedvtx;

    464:   PetscFunctionBegin;
    465:   PetscCall(KSPGetDM(ksp, &dm));

    467:   /* get the solution vector */
    468:   PetscCall(KSPGetSolution(ksp, &sol));

    470:   /* Get the internal reference to the vector arrays */
    471:   PetscCall(VecGetArrayRead(sol, &x));
    472:   PetscCall(VecGetSize(sol, &N));
    473:   if (err) {
    474:     /* reset the error vector */
    475:     PetscCall(VecSet(err, 0.0));
    476:     /* get array reference */
    477:     PetscCall(VecGetArray(err, &e));
    478:   }

    480:   PetscCall(DMMoabGetLocalVertices(dm, &ownedvtx, NULL));

    482:   /* Compute function over the locally owned part of the grid */
    483:   for (moab::Range::iterator iter = ownedvtx->begin(); iter != ownedvtx->end(); iter++) {
    484:     const moab::EntityHandle vhandle = *iter;
    485:     PetscCall(DMMoabGetDofsBlockedLocal(dm, 1, &vhandle, &dof_index));

    487:     /* compute the mid-point of the element and use a 1-point lumped quadrature */
    488:     PetscCall(DMMoabGetVertexCoordinates(dm, 1, &vhandle, vpos));

    490:     /* compute the discrete L2 error against the exact solution */
    491:     const PetscScalar lerr = (ExactSolution(vpos, user) - x[dof_index]);
    492:     l2err += lerr * lerr;
    493:     if (linferr < fabs(lerr)) linferr = fabs(lerr);

    495:     if (err) {
    496:       /* set the discrete L2 error against the exact solution */
    497:       e[dof_index] = lerr;
    498:     }
    499:   }

    501:   PetscCallMPI(MPIU_Allreduce(&l2err, &global_l2, 1, MPI_DOUBLE, MPI_SUM, PETSC_COMM_WORLD));
    502:   PetscCallMPI(MPIU_Allreduce(&linferr, &global_linf, 1, MPI_DOUBLE, MPI_MAX, PETSC_COMM_WORLD));
    503:   PetscCall(PetscPrintf(PETSC_COMM_WORLD, "Computed Errors: L_2 = %f, L_inf = %f\n", sqrt(global_l2 / N), global_linf));

    505:   /* Restore vectors */
    506:   PetscCall(VecRestoreArrayRead(sol, &x));
    507:   if (err) PetscCall(VecRestoreArray(err, &e));
    508:   PetscFunctionReturn(PETSC_SUCCESS);
    509: }

    511: PetscErrorCode InitializeOptions(UserContext *user)
    512: {
    513:   const char *bcTypes[2] = {"dirichlet", "neumann"};
    514:   PetscInt    bc;

    516:   PetscFunctionBegin;
    517:   /* set default parameters */
    518:   user->dim       = 3; /* 3-Dimensional problem */
    519:   user->problem   = 1;
    520:   user->n         = 2;
    521:   user->nlevels   = 2;
    522:   user->rho       = 0.1;
    523:   user->bounds[0] = user->bounds[2] = user->bounds[4] = 0.0;
    524:   user->bounds[1] = user->bounds[3] = user->bounds[5] = 1.0;
    525:   user->xyzref[0]                                     = user->bounds[1] / 2;
    526:   user->xyzref[1]                                     = user->bounds[3] / 2;
    527:   user->xyzref[2]                                     = user->bounds[5] / 2;
    528:   user->nu                                            = 0.05;
    529:   user->usemg                                         = PETSC_FALSE;
    530:   user->io                                            = PETSC_FALSE;
    531:   user->usetet                                        = PETSC_FALSE;
    532:   user->error                                         = PETSC_FALSE;
    533:   bc                                                  = (PetscInt)DIRICHLET;

    535:   PetscOptionsBegin(PETSC_COMM_WORLD, "", "Options for the inhomogeneous Poisson equation", "ex36.cxx");
    536:   PetscCall(PetscOptionsInt("-problem", "The type of problem being solved (controls forcing function)", "ex36.cxx", user->problem, &user->problem, NULL));
    537:   PetscCall(PetscOptionsInt("-n", "The elements in each direction", "ex36.cxx", user->n, &user->n, NULL));
    538:   PetscCall(PetscOptionsInt("-levels", "Number of levels in the multigrid hierarchy", "ex36.cxx", user->nlevels, &user->nlevels, NULL));
    539:   PetscCall(PetscOptionsReal("-rho", "The conductivity", "ex36.cxx", user->rho, &user->rho, NULL));
    540:   PetscCall(PetscOptionsReal("-x", "The domain size in x-direction", "ex36.cxx", user->bounds[1], &user->bounds[1], NULL));
    541:   PetscCall(PetscOptionsReal("-y", "The domain size in y-direction", "ex36.cxx", user->bounds[3], &user->bounds[3], NULL));
    542:   PetscCall(PetscOptionsReal("-z", "The domain size in y-direction", "ex36.cxx", user->bounds[5], &user->bounds[5], NULL));
    543:   PetscCall(PetscOptionsReal("-xref", "The x-coordinate of Gaussian center (for -problem 1)", "ex36.cxx", user->xyzref[0], &user->xyzref[0], NULL));
    544:   PetscCall(PetscOptionsReal("-yref", "The y-coordinate of Gaussian center (for -problem 1)", "ex36.cxx", user->xyzref[1], &user->xyzref[1], NULL));
    545:   PetscCall(PetscOptionsReal("-zref", "The y-coordinate of Gaussian center (for -problem 1)", "ex36.cxx", user->xyzref[2], &user->xyzref[2], NULL));
    546:   PetscCall(PetscOptionsReal("-nu", "The width of the Gaussian source (for -problem 1)", "ex36.cxx", user->nu, &user->nu, NULL));
    547:   PetscCall(PetscOptionsBool("-mg", "Use multigrid preconditioner", "ex36.cxx", user->usemg, &user->usemg, NULL));
    548:   PetscCall(PetscOptionsBool("-io", "Write out the solution and mesh data", "ex36.cxx", user->io, &user->io, NULL));
    549:   PetscCall(PetscOptionsBool("-tet", "Use tetrahedra to discretize the domain", "ex36.cxx", user->usetet, &user->usetet, NULL));
    550:   PetscCall(PetscOptionsBool("-error", "Compute the discrete L_2 and L_inf errors of the solution", "ex36.cxx", user->error, &user->error, NULL));
    551:   PetscCall(PetscOptionsEList("-bc", "Type of boundary condition", "ex36.cxx", bcTypes, 2, bcTypes[0], &bc, NULL));
    552:   PetscCall(PetscOptionsString("-file", "The mesh file for the problem", "ex36.cxx", "", user->filename, sizeof(user->filename), &user->use_extfile));
    553:   PetscOptionsEnd();

    555:   if (user->problem < 1 || user->problem > 2) user->problem = 1;
    556:   user->bcType = (BCType)bc;
    557:   user->VPERE  = (user->usetet ? 4 : 8);
    558:   PetscFunctionReturn(PETSC_SUCCESS);
    559: }

    561: /*TEST

    563:    build:
    564:       requires: moab !complex

    566:    test:
    567:       args: -levels 1 -nu .01 -n 4 -mg -ksp_converged_reason

    569:    test:
    570:       suffix: 2
    571:       nsize: 2
    572:       requires: hdf5
    573:       args: -levels 2 -nu .01 -n 2 -mg -ksp_converged_reason

    575: TEST*/