Actual source code: hmg.c

      1: #include <petscdm.h>
      2: #include <petsc/private/hashmapi.h>
      3: #include <petsc/private/matimpl.h>
      4: #include <petsc/private/pcmgimpl.h>
      5: #include <petsc/private/pcimpl.h>

      7: typedef struct {
      8:   PC        innerpc;       /* A MG inner PC (Hypre or PCGAMG) to setup interpolations and coarse operators  */
      9:   char     *innerpctype;   /* PCGAMG or PCHYPRE */
     10:   PetscBool reuseinterp;   /* A flag indicates if or not to reuse the interpolations */
     11:   PetscBool subcoarsening; /* If or not to use a subspace-based coarsening algorithm */
     12:   PetscBool usematmaij;    /* If or not to use MatMAIJ for saving memory */
     13:   PetscInt  component;     /* Which subspace is used for the subspace-based coarsening algorithm? */
     14: } PC_HMG;

     16: static PetscErrorCode PCHMGExtractSubMatrix_Private(Mat pmat, Mat *submat, MatReuse reuse, PetscInt component, PetscInt blocksize)
     17: {
     18:   IS       isrow;
     19:   PetscInt rstart, rend;
     20:   MPI_Comm comm;

     22:   PetscFunctionBegin;
     23:   PetscCall(PetscObjectGetComm((PetscObject)pmat, &comm));
     24:   PetscCheck(component < blocksize, comm, PETSC_ERR_ARG_INCOMP, "Component %" PetscInt_FMT " should be less than block size %" PetscInt_FMT " ", component, blocksize);
     25:   PetscCall(MatGetOwnershipRange(pmat, &rstart, &rend));
     26:   PetscCheck((rend - rstart) % blocksize == 0, comm, PETSC_ERR_ARG_INCOMP, "Block size %" PetscInt_FMT " is inconsistent for [%" PetscInt_FMT ", %" PetscInt_FMT ") ", blocksize, rstart, rend);
     27:   PetscCall(ISCreateStride(comm, (rend - rstart) / blocksize, rstart + component, blocksize, &isrow));
     28:   PetscCall(MatCreateSubMatrix(pmat, isrow, isrow, reuse, submat));
     29:   PetscCall(ISDestroy(&isrow));
     30:   PetscFunctionReturn(PETSC_SUCCESS);
     31: }

     33: static PetscErrorCode PCHMGExpandInterpolation_Private(Mat subinterp, Mat *interp, PetscInt blocksize)
     34: {
     35:   PetscInt           subrstart, subrend, subrowsize, subcolsize, subcstart, subcend, rowsize, colsize;
     36:   PetscInt           subrow, row, nz, *d_nnz, *o_nnz, i, j, dnz, onz, max_nz, *indices;
     37:   const PetscInt    *idx;
     38:   const PetscScalar *values;
     39:   MPI_Comm           comm;

     41:   PetscFunctionBegin;
     42:   PetscCall(PetscObjectGetComm((PetscObject)subinterp, &comm));
     43:   PetscCall(MatGetOwnershipRange(subinterp, &subrstart, &subrend));
     44:   subrowsize = subrend - subrstart;
     45:   rowsize    = subrowsize * blocksize;
     46:   PetscCall(PetscCalloc2(rowsize, &d_nnz, rowsize, &o_nnz));
     47:   PetscCall(MatGetOwnershipRangeColumn(subinterp, &subcstart, &subcend));
     48:   subcolsize = subcend - subcstart;
     49:   colsize    = subcolsize * blocksize;
     50:   max_nz     = 0;
     51:   for (subrow = subrstart; subrow < subrend; subrow++) {
     52:     PetscCall(MatGetRow(subinterp, subrow, &nz, &idx, NULL));
     53:     if (max_nz < nz) max_nz = nz;
     54:     dnz = 0;
     55:     onz = 0;
     56:     for (i = 0; i < nz; i++) {
     57:       if (idx[i] >= subcstart && idx[i] < subcend) dnz++;
     58:       else onz++;
     59:     }
     60:     for (i = 0; i < blocksize; i++) {
     61:       d_nnz[(subrow - subrstart) * blocksize + i] = dnz;
     62:       o_nnz[(subrow - subrstart) * blocksize + i] = onz;
     63:     }
     64:     PetscCall(MatRestoreRow(subinterp, subrow, &nz, &idx, NULL));
     65:   }
     66:   PetscCall(MatCreateAIJ(comm, rowsize, colsize, PETSC_DETERMINE, PETSC_DETERMINE, 0, d_nnz, 0, o_nnz, interp));
     67:   PetscCall(MatSetOption(*interp, MAT_IGNORE_OFF_PROC_ENTRIES, PETSC_TRUE));
     68:   PetscCall(MatSetOption(*interp, MAT_IGNORE_ZERO_ENTRIES, PETSC_TRUE));
     69:   PetscCall(MatSetOption(*interp, MAT_NEW_NONZERO_ALLOCATION_ERR, PETSC_TRUE));
     70:   PetscCall(MatSetFromOptions(*interp));

     72:   PetscCall(MatSetUp(*interp));
     73:   PetscCall(PetscFree2(d_nnz, o_nnz));
     74:   PetscCall(PetscMalloc1(max_nz, &indices));
     75:   for (subrow = subrstart; subrow < subrend; subrow++) {
     76:     PetscCall(MatGetRow(subinterp, subrow, &nz, &idx, &values));
     77:     for (i = 0; i < blocksize; i++) {
     78:       row = subrow * blocksize + i;
     79:       for (j = 0; j < nz; j++) indices[j] = idx[j] * blocksize + i;
     80:       PetscCall(MatSetValues(*interp, 1, &row, nz, indices, values, INSERT_VALUES));
     81:     }
     82:     PetscCall(MatRestoreRow(subinterp, subrow, &nz, &idx, &values));
     83:   }
     84:   PetscCall(PetscFree(indices));
     85:   PetscCall(MatAssemblyBegin(*interp, MAT_FINAL_ASSEMBLY));
     86:   PetscCall(MatAssemblyEnd(*interp, MAT_FINAL_ASSEMBLY));
     87:   PetscFunctionReturn(PETSC_SUCCESS);
     88: }

     90: static PetscErrorCode PCSetUp_HMG(PC pc)
     91: {
     92:   Mat              PA, submat;
     93:   PC_MG           *mg  = (PC_MG *)pc->data;
     94:   PC_HMG          *hmg = (PC_HMG *)mg->innerctx;
     95:   MPI_Comm         comm;
     96:   PetscInt         level;
     97:   PetscInt         num_levels;
     98:   Mat             *operators, *interpolations;
     99:   PetscInt         blocksize;
    100:   const char      *prefix;
    101:   PCMGGalerkinType galerkin;

    103:   PetscFunctionBegin;
    104:   PetscCall(PetscObjectGetComm((PetscObject)pc, &comm));
    105:   if (pc->setupcalled) {
    106:     if (hmg->reuseinterp) {
    107:       /* If we did not use Galerkin in the last call or we have a different sparsity pattern now,
    108:       * we have to build from scratch
    109:       * */
    110:       PetscCall(PCMGGetGalerkin(pc, &galerkin));
    111:       if (galerkin == PC_MG_GALERKIN_NONE || pc->flag != SAME_NONZERO_PATTERN) pc->setupcalled = PETSC_FALSE;
    112:       PetscCall(PCMGSetGalerkin(pc, PC_MG_GALERKIN_PMAT));
    113:       PetscCall(PCSetUp_MG(pc));
    114:       PetscFunctionReturn(PETSC_SUCCESS);
    115:     } else {
    116:       PetscCall(PCReset_MG(pc));
    117:       pc->setupcalled = PETSC_FALSE;
    118:     }
    119:   }

    121:   /* Create an inner PC (GAMG or HYPRE) */
    122:   if (!hmg->innerpc) {
    123:     PetscCall(PCCreate(comm, &hmg->innerpc));
    124:     /* If users do not set an inner pc type, we need to set a default value */
    125:     if (!hmg->innerpctype) {
    126:       /* If hypre is available, use hypre, otherwise, use gamg */
    127: #if PetscDefined(HAVE_HYPRE)
    128:       PetscCall(PetscStrallocpy(PCHYPRE, &hmg->innerpctype));
    129: #else
    130:       PetscCall(PetscStrallocpy(PCGAMG, &hmg->innerpctype));
    131: #endif
    132:     }
    133:     PetscCall(PCSetType(hmg->innerpc, hmg->innerpctype));
    134:   }
    135:   PetscCall(PCGetOperators(pc, NULL, &PA));
    136:   /* Users need to correctly set a block size of matrix in order to use subspace coarsening */
    137:   PetscCall(MatGetBlockSize(PA, &blocksize));
    138:   if (blocksize <= 1) hmg->subcoarsening = PETSC_FALSE;
    139:   /* Extract a submatrix for constructing subinterpolations */
    140:   if (hmg->subcoarsening) {
    141:     PetscCall(PCHMGExtractSubMatrix_Private(PA, &submat, MAT_INITIAL_MATRIX, hmg->component, blocksize));
    142:     PA = submat;
    143:   }
    144:   PetscCall(PCSetOperators(hmg->innerpc, PA, PA));
    145:   if (hmg->subcoarsening) PetscCall(MatDestroy(&PA));
    146:   /* Setup inner PC correctly. During this step, matrix will be coarsened */
    147:   PetscCall(PCSetUseAmat(hmg->innerpc, PETSC_FALSE));
    148:   PetscCall(PetscObjectGetOptionsPrefix((PetscObject)pc, &prefix));
    149:   PetscCall(PetscObjectSetOptionsPrefix((PetscObject)hmg->innerpc, prefix));
    150:   PetscCall(PetscObjectAppendOptionsPrefix((PetscObject)hmg->innerpc, "hmg_inner_"));
    151:   PetscCall(PCSetFromOptions(hmg->innerpc));
    152:   PetscCall(PCSetUp(hmg->innerpc));

    154:   /* Obtain interpolations IN PLACE. For BoomerAMG, (I,J,data) is reused to avoid memory overhead */
    155:   PetscCall(PCGetInterpolations(hmg->innerpc, &num_levels, &interpolations));
    156:   /* We can reuse the coarse operators when we do the full space coarsening */
    157:   if (!hmg->subcoarsening) PetscCall(PCGetCoarseOperators(hmg->innerpc, &num_levels, &operators));

    159:   PetscCall(PCDestroy(&hmg->innerpc));
    160:   hmg->innerpc = NULL;
    161:   PetscCall(PCMGSetLevels_MG(pc, num_levels, NULL));
    162:   /* Set coarse matrices and interpolations to PCMG */
    163:   for (level = num_levels - 1; level > 0; level--) {
    164:     Mat P = NULL, pmat = NULL;
    165:     Vec b, x, r;
    166:     if (hmg->subcoarsening) {
    167:       if (hmg->usematmaij) {
    168:         PetscCall(MatCreateMAIJ(interpolations[level - 1], blocksize, &P));
    169:         PetscCall(MatDestroy(&interpolations[level - 1]));
    170:       } else {
    171:         /* Grow interpolation. In the future, we should use MAIJ */
    172:         PetscCall(PCHMGExpandInterpolation_Private(interpolations[level - 1], &P, blocksize));
    173:         PetscCall(MatDestroy(&interpolations[level - 1]));
    174:       }
    175:     } else {
    176:       P = interpolations[level - 1];
    177:     }
    178:     PetscCall(MatCreateVecs(P, &b, &r));
    179:     PetscCall(PCMGSetInterpolation(pc, level, P));
    180:     PetscCall(PCMGSetRestriction(pc, level, P));
    181:     PetscCall(MatDestroy(&P));
    182:     /* We reuse the matrices when we do not do subspace coarsening */
    183:     if ((level - 1) >= 0 && !hmg->subcoarsening) {
    184:       pmat = operators[level - 1];
    185:       PetscCall(PCMGSetOperators(pc, level - 1, pmat, pmat));
    186:       PetscCall(MatDestroy(&pmat));
    187:     }
    188:     PetscCall(PCMGSetRhs(pc, level - 1, b));

    190:     PetscCall(PCMGSetR(pc, level, r));
    191:     PetscCall(VecDestroy(&r));

    193:     PetscCall(VecDuplicate(b, &x));
    194:     PetscCall(PCMGSetX(pc, level - 1, x));
    195:     PetscCall(VecDestroy(&x));
    196:     PetscCall(VecDestroy(&b));
    197:   }
    198:   PetscCall(PetscFree(interpolations));
    199:   if (!hmg->subcoarsening) PetscCall(PetscFree(operators));
    200:   /* Turn Galerkin off when we already have coarse operators */
    201:   PetscCall(PCMGSetGalerkin(pc, hmg->subcoarsening ? PC_MG_GALERKIN_PMAT : PC_MG_GALERKIN_NONE));
    202:   PetscCall(PCSetDM(pc, NULL));
    203:   PetscCall(PCSetUseAmat(pc, PETSC_FALSE));
    204:   PetscObjectOptionsBegin((PetscObject)pc);
    205:   PetscCall(PCSetFromOptions_MG(pc, PetscOptionsObject)); /* should be called in PCSetFromOptions_HMG(), but cannot be called prior to PCMGSetLevels() */
    206:   PetscOptionsEnd();
    207:   PetscCall(PCSetUp_MG(pc));
    208:   PetscFunctionReturn(PETSC_SUCCESS);
    209: }

    211: static PetscErrorCode PCDestroy_HMG(PC pc)
    212: {
    213:   PC_MG  *mg  = (PC_MG *)pc->data;
    214:   PC_HMG *hmg = (PC_HMG *)mg->innerctx;

    216:   PetscFunctionBegin;
    217:   PetscCall(PCDestroy(&hmg->innerpc));
    218:   PetscCall(PetscFree(hmg->innerpctype));
    219:   PetscCall(PetscFree(hmg));
    220:   PetscCall(PCDestroy_MG(pc));

    222:   PetscCall(PetscObjectComposeFunction((PetscObject)pc, "PCHMGSetReuseInterpolation_C", NULL));
    223:   PetscCall(PetscObjectComposeFunction((PetscObject)pc, "PCHMGSetUseSubspaceCoarsening_C", NULL));
    224:   PetscCall(PetscObjectComposeFunction((PetscObject)pc, "PCHMGSetInnerPCType_C", NULL));
    225:   PetscCall(PetscObjectComposeFunction((PetscObject)pc, "PCHMGSetCoarseningComponent_C", NULL));
    226:   PetscCall(PetscObjectComposeFunction((PetscObject)pc, "PCHMGUseMatMAIJ_C", NULL));
    227:   PetscFunctionReturn(PETSC_SUCCESS);
    228: }

    230: static PetscErrorCode PCView_HMG(PC pc, PetscViewer viewer)
    231: {
    232:   PC_MG    *mg  = (PC_MG *)pc->data;
    233:   PC_HMG   *hmg = (PC_HMG *)mg->innerctx;
    234:   PetscBool isascii;

    236:   PetscFunctionBegin;
    237:   PetscCall(PetscObjectTypeCompare((PetscObject)viewer, PETSCVIEWERASCII, &isascii));
    238:   if (isascii) {
    239:     PetscCall(PetscViewerASCIIPrintf(viewer, " Reuse interpolation: %s\n", hmg->reuseinterp ? "true" : "false"));
    240:     PetscCall(PetscViewerASCIIPrintf(viewer, " Use subspace coarsening: %s\n", hmg->subcoarsening ? "true" : "false"));
    241:     PetscCall(PetscViewerASCIIPrintf(viewer, " Coarsening component: %" PetscInt_FMT " \n", hmg->component));
    242:     PetscCall(PetscViewerASCIIPrintf(viewer, " Use MatMAIJ: %s \n", hmg->usematmaij ? "true" : "false"));
    243:     PetscCall(PetscViewerASCIIPrintf(viewer, " Inner PC type: %s \n", hmg->innerpctype));
    244:   }
    245:   PetscCall(PCView_MG(pc, viewer));
    246:   PetscFunctionReturn(PETSC_SUCCESS);
    247: }

    249: static PetscErrorCode PCSetFromOptions_HMG(PC pc, PetscOptionItems PetscOptionsObject)
    250: {
    251:   PC_MG  *mg  = (PC_MG *)pc->data;
    252:   PC_HMG *hmg = (PC_HMG *)mg->innerctx;

    254:   PetscFunctionBegin;
    255:   PetscOptionsHeadBegin(PetscOptionsObject, "HMG");
    256:   PetscCall(PetscOptionsBool("-pc_hmg_reuse_interpolation", "Reuse the interpolation operators when possible (cheaper, weaker when matrix entries change a lot)", "PCHMGSetReuseInterpolation", hmg->reuseinterp, &hmg->reuseinterp, NULL));
    257:   PetscCall(PetscOptionsBool("-pc_hmg_use_subspace_coarsening", "Use the subspace coarsening to compute the interpolations", "PCHMGSetUseSubspaceCoarsening", hmg->subcoarsening, &hmg->subcoarsening, NULL));
    258:   PetscCall(PetscOptionsBool("-pc_hmg_use_matmaij", "Use MatMAIJ store interpolation for saving memory", "PCHMGSetInnerPCType", hmg->usematmaij, &hmg->usematmaij, NULL));
    259:   PetscCall(PetscOptionsInt("-pc_hmg_coarsening_component", "Which component is chosen for the subspace-based coarsening algorithm", "PCHMGSetCoarseningComponent", hmg->component, &hmg->component, NULL));
    260:   PetscOptionsHeadEnd();
    261:   PetscFunctionReturn(PETSC_SUCCESS);
    262: }

    264: static PetscErrorCode PCHMGSetReuseInterpolation_HMG(PC pc, PetscBool reuse)
    265: {
    266:   PC_MG  *mg  = (PC_MG *)pc->data;
    267:   PC_HMG *hmg = (PC_HMG *)mg->innerctx;

    269:   PetscFunctionBegin;
    270:   hmg->reuseinterp = reuse;
    271:   PetscFunctionReturn(PETSC_SUCCESS);
    272: }

    274: /*@
    275:   PCHMGSetReuseInterpolation - Reuse the interpolation matrices in `PCHMG` after changing the matrices numerical values

    277:   Logically Collective

    279:   Input Parameters:
    280: + pc    - the `PCHMG` context
    281: - reuse - `PETSC_TRUE` indicates that `PCHMG` will reuse the interpolations

    283:   Options Database Key:
    284: . -pc_hmg_reuse_interpolation (true|false) - Whether or not to reuse the interpolations. If true, it potentially save the compute time.

    286:   Level: beginner

    288:   Note:
    289:   This decreases the set up time of the `PC` significantly but may slow the convergence of the iterative method, `KSP`, that is using the `PCHMG`

    291: .seealso: [](ch_ksp), `PCHMG`, `PCGAMG`, `PCHMGSetUseSubspaceCoarsening()`, `PCHMGSetCoarseningComponent()`, `PCHMGSetInnerPCType()`
    292: @*/
    293: PetscErrorCode PCHMGSetReuseInterpolation(PC pc, PetscBool reuse)
    294: {
    295:   PetscFunctionBegin;
    297:   PetscUseMethod(pc, "PCHMGSetReuseInterpolation_C", (PC, PetscBool), (pc, reuse));
    298:   PetscFunctionReturn(PETSC_SUCCESS);
    299: }

    301: static PetscErrorCode PCHMGSetUseSubspaceCoarsening_HMG(PC pc, PetscBool subspace)
    302: {
    303:   PC_MG  *mg  = (PC_MG *)pc->data;
    304:   PC_HMG *hmg = (PC_HMG *)mg->innerctx;

    306:   PetscFunctionBegin;
    307:   hmg->subcoarsening = subspace;
    308:   PetscFunctionReturn(PETSC_SUCCESS);
    309: }

    311: /*@
    312:   PCHMGSetUseSubspaceCoarsening - Use subspace coarsening in `PCHMG`

    314:   Logically Collective

    316:   Input Parameters:
    317: + pc       - the `PCHMG` context
    318: - subspace - `PETSC_TRUE` indicates that `PCHMG` will use the subspace coarsening

    320:   Options Database Key:
    321: . -pc_hmg_use_subspace_coarsening  (true|false) - Whether or not to use subspace coarsening (that is, coarsen a submatrix).

    323:   Level: beginner

    325: .seealso: [](ch_ksp), `PCHMG`, `PCHMGSetReuseInterpolation()`, `PCHMGSetCoarseningComponent()`, `PCHMGSetInnerPCType()`
    326: @*/
    327: PetscErrorCode PCHMGSetUseSubspaceCoarsening(PC pc, PetscBool subspace)
    328: {
    329:   PetscFunctionBegin;
    331:   PetscUseMethod(pc, "PCHMGSetUseSubspaceCoarsening_C", (PC, PetscBool), (pc, subspace));
    332:   PetscFunctionReturn(PETSC_SUCCESS);
    333: }

    335: static PetscErrorCode PCHMGSetInnerPCType_HMG(PC pc, PCType type)
    336: {
    337:   PC_MG  *mg  = (PC_MG *)pc->data;
    338:   PC_HMG *hmg = (PC_HMG *)mg->innerctx;

    340:   PetscFunctionBegin;
    341:   PetscCall(PetscStrallocpy(type, &hmg->innerpctype));
    342:   PetscFunctionReturn(PETSC_SUCCESS);
    343: }

    345: /*@
    346:   PCHMGSetInnerPCType - Set an inner `PC` type to be used in the `PCHMG` preconditioner. That is the method used to compute
    347:   the hierarchy of restriction operators.

    349:   Logically Collective

    351:   Input Parameters:
    352: + pc   - the `PCHMG` context
    353: - type - `PCHYPRE` or `PCGAMG` coarsening algorithm

    355:   Options Database Key:
    356: . -hmg_inner_pc_type (hypre|gamg) - What method is used to coarsen matrix

    358:   Level: beginner

    360: .seealso: [](ch_ksp), `PCHMG`, `PCType`, `PCHMGSetReuseInterpolation()`, `PCHMGSetUseSubspaceCoarsening()`, `PCHMGSetCoarseningComponent()`
    361: @*/
    362: PetscErrorCode PCHMGSetInnerPCType(PC pc, PCType type)
    363: {
    364:   PetscFunctionBegin;
    366:   PetscUseMethod(pc, "PCHMGSetInnerPCType_C", (PC, PCType), (pc, type));
    367:   PetscFunctionReturn(PETSC_SUCCESS);
    368: }

    370: static PetscErrorCode PCHMGSetCoarseningComponent_HMG(PC pc, PetscInt component)
    371: {
    372:   PC_MG  *mg  = (PC_MG *)pc->data;
    373:   PC_HMG *hmg = (PC_HMG *)mg->innerctx;

    375:   PetscFunctionBegin;
    376:   hmg->component = component;
    377:   PetscFunctionReturn(PETSC_SUCCESS);
    378: }

    380: /*@
    381:   PCHMGSetCoarseningComponent - Set which component of the PDE is used for the subspace-based coarsening algorithm in the preconditioner `PCHMG`

    383:   Logically Collective

    385:   Input Parameters:
    386: + pc        - the `PCHMG` context
    387: - component - which component `PC` will coarsen

    389:   Options Database Key:
    390: . -pc_hmg_coarsening_component i - Which component is chosen for the subspace-based coarsening algorithm

    392:   Level: beginner

    394:   Note:
    395:   By default it uses the first component

    397: .seealso: [](ch_ksp), `PCHMG`, `PCType`, `PCGAMG`, `PCHMGSetReuseInterpolation()`, `PCHMGSetUseSubspaceCoarsening()`, `PCHMGSetInnerPCType()`
    398: @*/
    399: PetscErrorCode PCHMGSetCoarseningComponent(PC pc, PetscInt component)
    400: {
    401:   PetscFunctionBegin;
    403:   PetscUseMethod(pc, "PCHMGSetCoarseningComponent_C", (PC, PetscInt), (pc, component));
    404:   PetscFunctionReturn(PETSC_SUCCESS);
    405: }

    407: static PetscErrorCode PCHMGUseMatMAIJ_HMG(PC pc, PetscBool usematmaij)
    408: {
    409:   PC_MG  *mg  = (PC_MG *)pc->data;
    410:   PC_HMG *hmg = (PC_HMG *)mg->innerctx;

    412:   PetscFunctionBegin;
    413:   hmg->usematmaij = usematmaij;
    414:   PetscFunctionReturn(PETSC_SUCCESS);
    415: }

    417: /*@
    418:   PCHMGUseMatMAIJ - Set a flag that indicates if or not to use `MATMAIJ` for the interpolation matrices to save memory

    420:   Logically Collective

    422:   Input Parameters:
    423: + pc         - the `PCHMG` context
    424: - usematmaij - `PETSC_TRUE` (default) to use `MATMAIJ` for interpolations.

    426:   Options Database Key:
    427: . -pc_hmg_use_matmaij (true|false) - use `MATMAIJ` for interpolations

    429:   Level: beginner

    431: .seealso: [](ch_ksp), `PCHMG`, `PCType`, `PCGAMG`
    432: @*/
    433: PetscErrorCode PCHMGUseMatMAIJ(PC pc, PetscBool usematmaij)
    434: {
    435:   PetscFunctionBegin;
    437:   PetscUseMethod(pc, "PCHMGUseMatMAIJ_C", (PC, PetscBool), (pc, usematmaij));
    438:   PetscFunctionReturn(PETSC_SUCCESS);
    439: }

    441: /*MC
    442:    PCHMG - Preconditioner for multiple component PDE problems that constructs a hierarchy of restriction operators to coarse grid problems using the submatrix of
    443:    a single component with either `PCHYPRE` or `PCGAMG`. The same restriction operators are then used for each of the components of the PDE within the `PCMG`
    444:    multigrid preconditioner. This results in a much more efficient to build and apply preconditioner than using `PCGAMG` on the entire system {cite}`kong2020highly`.

    446:    Options Database Keys:
    447: +  -pc_hmg_reuse_interpolation (true|false)      - Whether or not to reuse the interpolations for new matrix values or rebuild the interpolation. This can save compute time.
    448: .  -pc_hmg_use_subspace_coarsening  (true|false) - Whether or not to use subspace coarsening (that is, coarsen a submatrix, or coarsen on the full matrix).
    449: .  -hmg_inner_pc_type (hypre|gamg)               - What method to use to generate the hierarchy of restriction operators
    450: -  -pc_hmg_use_matmaij (true|false)              - Whether or not to use `MATMAIJ` for multicomponent problems for saving memory

    452:    Level: intermediate

    454:    Note:
    455:    `MatSetBlockSize()` must be called on the linear system matrix to set the number of components of the PDE.

    457: .seealso: [](ch_ksp), `PCCreate()`, `PCSetType()`, `PCType`, `PC`, `PCMG`, `PCHYPRE`, `PCHMG`, `PCGetCoarseOperators()`, `PCGetInterpolations()`,
    458:           `PCHMGSetReuseInterpolation()`, `PCHMGSetUseSubspaceCoarsening()`, `PCHMGSetInnerPCType()`, `PCGAMG`
    459: M*/
    460: PETSC_EXTERN PetscErrorCode PCCreate_HMG(PC pc)
    461: {
    462:   PC_HMG *hmg;
    463:   PC_MG  *mg;

    465:   PetscFunctionBegin;
    466:   /* if type was previously mg; must manually destroy it because call to PCSetType(pc,PCMG) will not destroy it */
    467:   PetscTryTypeMethod(pc, destroy);
    468:   pc->data = NULL;
    469:   PetscCall(PetscFree(((PetscObject)pc)->type_name));

    471:   PetscCall(PCSetType(pc, PCMG));
    472:   PetscCall(PetscObjectChangeTypeName((PetscObject)pc, PCHMG));
    473:   PetscCall(PetscNew(&hmg));

    475:   mg                 = (PC_MG *)pc->data;
    476:   mg->innerctx       = hmg;
    477:   hmg->reuseinterp   = PETSC_FALSE;
    478:   hmg->subcoarsening = PETSC_FALSE;
    479:   hmg->usematmaij    = PETSC_TRUE;
    480:   hmg->component     = 0;
    481:   hmg->innerpc       = NULL;

    483:   pc->ops->setfromoptions = PCSetFromOptions_HMG;
    484:   pc->ops->view           = PCView_HMG;
    485:   pc->ops->destroy        = PCDestroy_HMG;
    486:   pc->ops->setup          = PCSetUp_HMG;

    488:   PetscCall(PetscObjectComposeFunction((PetscObject)pc, "PCHMGSetReuseInterpolation_C", PCHMGSetReuseInterpolation_HMG));
    489:   PetscCall(PetscObjectComposeFunction((PetscObject)pc, "PCHMGSetUseSubspaceCoarsening_C", PCHMGSetUseSubspaceCoarsening_HMG));
    490:   PetscCall(PetscObjectComposeFunction((PetscObject)pc, "PCHMGSetInnerPCType_C", PCHMGSetInnerPCType_HMG));
    491:   PetscCall(PetscObjectComposeFunction((PetscObject)pc, "PCHMGSetCoarseningComponent_C", PCHMGSetCoarseningComponent_HMG));
    492:   PetscCall(PetscObjectComposeFunction((PetscObject)pc, "PCHMGUseMatMAIJ_C", PCHMGUseMatMAIJ_HMG));
    493:   PetscFunctionReturn(PETSC_SUCCESS);
    494: }