Actual source code: telescope.c

  1: #include <petsc/private/petscimpl.h>
  2: #include <petsc/private/matimpl.h>
  3: #include <petsc/private/pcimpl.h>
  4: #include <petscksp.h>
  5: #include <petscdm.h>
  6: #include "../src/ksp/pc/impls/telescope/telescope.h"

  8: static PetscBool  cited      = PETSC_FALSE;
  9: static const char citation[] = "@inproceedings{MaySananRuppKnepleySmith2016,\n"
 10:                                "  title     = {Extreme-Scale Multigrid Components within PETSc},\n"
 11:                                "  author    = {Dave A. May and Patrick Sanan and Karl Rupp and Matthew G. Knepley and Barry F. Smith},\n"
 12:                                "  booktitle = {Proceedings of the Platform for Advanced Scientific Computing Conference},\n"
 13:                                "  series    = {PASC '16},\n"
 14:                                "  isbn      = {978-1-4503-4126-4},\n"
 15:                                "  location  = {Lausanne, Switzerland},\n"
 16:                                "  pages     = {5:1--5:12},\n"
 17:                                "  articleno = {5},\n"
 18:                                "  numpages  = {12},\n"
 19:                                "  url       = {https://doi.acm.org/10.1145/2929908.2929913},\n"
 20:                                "  doi       = {10.1145/2929908.2929913},\n"
 21:                                "  acmid     = {2929913},\n"
 22:                                "  publisher = {ACM},\n"
 23:                                "  address   = {New York, NY, USA},\n"
 24:                                "  keywords  = {GPU, HPC, agglomeration, coarse-level solver, multigrid, parallel computing, preconditioning},\n"
 25:                                "  year      = {2016}\n"
 26:                                "}\n";

 28: /*
 29:  default setup mode

 31:  [1a] scatter to (FORWARD)
 32:  x(comm) -> xtmp(comm)
 33:  [1b] local copy (to) ranks with color = 0
 34:  xred(subcomm) <- xtmp

 36:  [2] solve on sub KSP to obtain yred(subcomm)

 38:  [3a] local copy (from) ranks with color = 0
 39:  yred(subcomm) --> xtmp
 40:  [2b] scatter from (REVERSE)
 41:  xtmp(comm) -> y(comm)
 42: */

 44: /*
 45:   Collective[comm_f]
 46:   Notes
 47:    * Using comm_f = MPI_COMM_NULL will result in an error
 48:    * Using comm_c = MPI_COMM_NULL is valid. If all instances of comm_c are NULL the subcomm is not valid.
 49:    * If any non NULL comm_c communicator cannot map any of its ranks to comm_f, the subcomm is not valid.
 50: */
 51: static PetscErrorCode PCTelescopeTestValidSubcomm(MPI_Comm comm_f, MPI_Comm comm_c, PetscBool *isvalid)
 52: {
 53:   PetscInt     valid = 1;
 54:   MPI_Group    group_f, group_c;
 55:   PetscMPIInt  count, k, size_f = 0, size_c = 0, size_c_sum = 0;
 56:   PetscMPIInt *ranks_f, *ranks_c;

 58:   PetscFunctionBegin;
 59:   PetscCheck(comm_f != MPI_COMM_NULL, PETSC_COMM_SELF, PETSC_ERR_SUP, "comm_f cannot be MPI_COMM_NULL");

 61:   PetscCallMPI(MPI_Comm_group(comm_f, &group_f));
 62:   if (comm_c != MPI_COMM_NULL) PetscCallMPI(MPI_Comm_group(comm_c, &group_c));

 64:   PetscCallMPI(MPI_Comm_size(comm_f, &size_f));
 65:   if (comm_c != MPI_COMM_NULL) PetscCallMPI(MPI_Comm_size(comm_c, &size_c));

 67:   /* check not all comm_c's are NULL */
 68:   size_c_sum = size_c;
 69:   PetscCallMPI(MPIU_Allreduce(MPI_IN_PLACE, &size_c_sum, 1, MPI_INT, MPI_SUM, comm_f));
 70:   if (size_c_sum == 0) valid = 0;

 72:   /* check we can map at least 1 rank in comm_c to comm_f */
 73:   PetscCall(PetscMalloc1(size_f, &ranks_f));
 74:   PetscCall(PetscMalloc1(size_c, &ranks_c));
 75:   for (k = 0; k < size_f; k++) ranks_f[k] = MPI_UNDEFINED;
 76:   for (k = 0; k < size_c; k++) ranks_c[k] = k;

 78:   /*
 79:    MPI_Group_translate_ranks() returns a non-zero exit code if any rank cannot be translated.
 80:    I do not want the code to terminate immediately if this occurs, rather I want to throw
 81:    the error later (during PCSetUp_Telescope()) via SETERRQ() with a message indicating
 82:    that comm_c is not a valid sub-communicator.
 83:    Hence I purposefully do not call PetscCall() after MPI_Group_translate_ranks().
 84:   */
 85:   count = 0;
 86:   if (comm_c != MPI_COMM_NULL) {
 87:     (void)MPI_Group_translate_ranks(group_c, size_c, ranks_c, group_f, ranks_f);
 88:     for (k = 0; k < size_f; k++) {
 89:       if (ranks_f[k] == MPI_UNDEFINED) count++;
 90:     }
 91:   }
 92:   if (count == size_f) valid = 0;

 94:   PetscCallMPI(MPIU_Allreduce(MPI_IN_PLACE, &valid, 1, MPIU_INT, MPI_MIN, comm_f));
 95:   if (valid == 1) *isvalid = PETSC_TRUE;
 96:   else *isvalid = PETSC_FALSE;

 98:   PetscCall(PetscFree(ranks_f));
 99:   PetscCall(PetscFree(ranks_c));
100:   PetscCallMPI(MPI_Group_free(&group_f));
101:   if (comm_c != MPI_COMM_NULL) PetscCallMPI(MPI_Group_free(&group_c));
102:   PetscFunctionReturn(PETSC_SUCCESS);
103: }

105: static DM private_PCTelescopeGetSubDM(PC_Telescope sred)
106: {
107:   DM subdm = NULL;

109:   if (!PCTelescope_isActiveRank(sred)) {
110:     subdm = NULL;
111:   } else {
112:     switch (sred->sr_type) {
113:     case TELESCOPE_DEFAULT:
114:       subdm = NULL;
115:       break;
116:     case TELESCOPE_DMDA:
117:       subdm = ((PC_Telescope_DMDACtx *)sred->dm_ctx)->dmrepart;
118:       break;
119:     case TELESCOPE_DMPLEX:
120:       subdm = NULL;
121:       break;
122:     case TELESCOPE_COARSEDM:
123:       if (sred->ksp) PetscCallAbort(PETSC_COMM_SELF, KSPGetDM(sred->ksp, &subdm));
124:       break;
125:     }
126:   }
127:   return subdm;
128: }

130: static PetscErrorCode PCTelescopeSetUp_default(PC pc, PC_Telescope sred)
131: {
132:   PetscInt   m, M, bs, st, ed;
133:   Vec        x, xred, yred, xtmp;
134:   Mat        B;
135:   MPI_Comm   comm, subcomm;
136:   VecScatter scatter;
137:   IS         isin;
138:   VecType    vectype;

140:   PetscFunctionBegin;
141:   PetscCall(PetscInfo(pc, "PCTelescope: setup (default)\n"));
142:   comm    = PetscSubcommParent(sred->psubcomm);
143:   subcomm = PetscSubcommChild(sred->psubcomm);

145:   PetscCall(PCGetOperators(pc, NULL, &B));
146:   PetscCall(MatGetSize(B, &M, NULL));
147:   PetscCall(MatGetBlockSize(B, &bs));
148:   PetscCall(MatCreateVecs(B, &x, NULL));
149:   PetscCall(MatGetVecType(B, &vectype)); /* Use the vectype of the matrix used to construct the preconditioner by default */

151:   xred = NULL;
152:   m    = 0;
153:   if (PCTelescope_isActiveRank(sred)) {
154:     PetscCall(VecCreate(subcomm, &xred));
155:     PetscCall(VecSetSizes(xred, PETSC_DECIDE, M));
156:     PetscCall(VecSetBlockSize(xred, bs));
157:     PetscCall(VecSetType(xred, vectype));
158:     PetscCall(VecSetFromOptions(xred));
159:     PetscCall(VecGetLocalSize(xred, &m));
160:   }

162:   yred = NULL;
163:   if (PCTelescope_isActiveRank(sred)) PetscCall(VecDuplicate(xred, &yred));

165:   PetscCall(VecCreate(comm, &xtmp));
166:   PetscCall(VecSetSizes(xtmp, m, PETSC_DECIDE));
167:   PetscCall(VecSetBlockSize(xtmp, bs));
168:   PetscCall(VecSetType(xtmp, vectype));

170:   if (PCTelescope_isActiveRank(sred)) {
171:     PetscCall(VecGetOwnershipRange(xred, &st, &ed));
172:     PetscCall(ISCreateStride(comm, ed - st, st, 1, &isin));
173:   } else {
174:     PetscCall(VecGetOwnershipRange(x, &st, &ed));
175:     PetscCall(ISCreateStride(comm, 0, st, 1, &isin));
176:   }
177:   PetscCall(ISSetBlockSize(isin, bs));

179:   PetscCall(VecScatterCreate(x, isin, xtmp, NULL, &scatter));

181:   sred->isin    = isin;
182:   sred->scatter = scatter;
183:   sred->xred    = xred;
184:   sred->yred    = yred;
185:   sred->xtmp    = xtmp;
186:   PetscCall(VecDestroy(&x));
187:   PetscFunctionReturn(PETSC_SUCCESS);
188: }

190: static PetscErrorCode PCTelescopeMatCreate_default(PC pc, PC_Telescope sred, MatReuse reuse, Mat *A)
191: {
192:   MPI_Comm comm, subcomm;
193:   Mat      Bred, B;
194:   PetscInt nr, nc, bs;
195:   IS       isrow, iscol;
196:   Mat      Blocal, *_Blocal;

198:   PetscFunctionBegin;
199:   PetscCall(PetscInfo(pc, "PCTelescope: updating the redundant preconditioned operator (default)\n"));
200:   PetscCall(PetscObjectGetComm((PetscObject)pc, &comm));
201:   subcomm = PetscSubcommChild(sred->psubcomm);
202:   PetscCall(PCGetOperators(pc, NULL, &B));
203:   PetscCall(MatGetSize(B, &nr, &nc));
204:   isrow = sred->isin;
205:   PetscCall(ISCreateStride(PETSC_COMM_SELF, nc, 0, 1, &iscol));
206:   PetscCall(ISSetIdentity(iscol));
207:   PetscCall(MatGetBlockSizes(B, NULL, &bs));
208:   PetscCall(ISSetBlockSize(iscol, bs));
209:   PetscCall(MatSetOption(B, MAT_SUBMAT_SINGLEIS, PETSC_TRUE));
210:   PetscCall(MatCreateSubMatrices(B, 1, &isrow, &iscol, MAT_INITIAL_MATRIX, &_Blocal));
211:   Blocal = *_Blocal;
212:   PetscCall(PetscFree(_Blocal));
213:   Bred = NULL;
214:   if (PCTelescope_isActiveRank(sred)) {
215:     PetscInt mm;

217:     if (reuse != MAT_INITIAL_MATRIX) Bred = *A;

219:     PetscCall(MatGetSize(Blocal, &mm, NULL));
220:     PetscCall(MatCreateMPIMatConcatenateSeqMat(subcomm, Blocal, mm, reuse, &Bred));
221:     PetscCall(MatPropagateSymmetryOptions(B, Bred));
222:   }
223:   *A = Bred;
224:   PetscCall(ISDestroy(&iscol));
225:   PetscCall(MatDestroy(&Blocal));
226:   PetscFunctionReturn(PETSC_SUCCESS);
227: }

229: static PetscErrorCode PCTelescopeSubNullSpaceCreate_Telescope(PC pc, PC_Telescope sred, MatNullSpace nullspace, MatNullSpace *sub_nullspace)
230: {
231:   PetscBool  has_const;
232:   const Vec *vecs;
233:   Vec       *sub_vecs = NULL;
234:   PetscInt   i, k, n = 0;
235:   MPI_Comm   subcomm;

237:   PetscFunctionBegin;
238:   subcomm = PetscSubcommChild(sred->psubcomm);
239:   PetscCall(MatNullSpaceGetVecs(nullspace, &has_const, &n, &vecs));

241:   if (PCTelescope_isActiveRank(sred)) {
242:     if (n) PetscCall(VecDuplicateVecs(sred->xred, n, &sub_vecs));
243:   }

245:   /* copy entries */
246:   for (k = 0; k < n; k++) {
247:     const PetscScalar *x_array;
248:     PetscScalar       *LA_sub_vec;
249:     PetscInt           st, ed;

251:     /* pull in vector x->xtmp */
252:     PetscCall(VecScatterBegin(sred->scatter, vecs[k], sred->xtmp, INSERT_VALUES, SCATTER_FORWARD));
253:     PetscCall(VecScatterEnd(sred->scatter, vecs[k], sred->xtmp, INSERT_VALUES, SCATTER_FORWARD));
254:     if (sub_vecs) {
255:       /* copy vector entries into xred */
256:       PetscCall(VecGetArrayRead(sred->xtmp, &x_array));
257:       if (sub_vecs[k]) {
258:         PetscCall(VecGetOwnershipRange(sub_vecs[k], &st, &ed));
259:         PetscCall(VecGetArray(sub_vecs[k], &LA_sub_vec));
260:         for (i = 0; i < ed - st; i++) LA_sub_vec[i] = x_array[i];
261:         PetscCall(VecRestoreArray(sub_vecs[k], &LA_sub_vec));
262:       }
263:       PetscCall(VecRestoreArrayRead(sred->xtmp, &x_array));
264:     }
265:   }

267:   if (PCTelescope_isActiveRank(sred)) {
268:     /* create new (near) nullspace for redundant object */
269:     PetscCall(MatNullSpaceCreate(subcomm, has_const, n, sub_vecs, sub_nullspace));
270:     PetscCall(VecDestroyVecs(n, &sub_vecs));
271:     PetscCheck(!nullspace->remove, PetscObjectComm((PetscObject)pc), PETSC_ERR_SUP, "Propagation of custom remove callbacks not supported when propagating (near) nullspaces with PCTelescope");
272:     PetscCheck(!nullspace->rmctx, PetscObjectComm((PetscObject)pc), PETSC_ERR_SUP, "Propagation of custom remove callback context not supported when propagating (near) nullspaces with PCTelescope");
273:   }
274:   PetscFunctionReturn(PETSC_SUCCESS);
275: }

277: static PetscErrorCode PCTelescopeMatNullSpaceCreate_default(PC pc, PC_Telescope sred, Mat sub_mat)
278: {
279:   Mat B;

281:   PetscFunctionBegin;
282:   PetscCall(PCGetOperators(pc, NULL, &B));
283:   /* Propagate the nullspace if it exists */
284:   {
285:     MatNullSpace nullspace, sub_nullspace;
286:     PetscCall(MatGetNullSpace(B, &nullspace));
287:     if (nullspace) {
288:       PetscCall(PetscInfo(pc, "PCTelescope: generating nullspace (default)\n"));
289:       PetscCall(PCTelescopeSubNullSpaceCreate_Telescope(pc, sred, nullspace, &sub_nullspace));
290:       if (PCTelescope_isActiveRank(sred)) {
291:         PetscCall(MatSetNullSpace(sub_mat, sub_nullspace));
292:         PetscCall(MatNullSpaceDestroy(&sub_nullspace));
293:       }
294:     }
295:   }
296:   /* Propagate the near nullspace if it exists */
297:   {
298:     MatNullSpace nearnullspace, sub_nearnullspace;
299:     PetscCall(MatGetNearNullSpace(B, &nearnullspace));
300:     if (nearnullspace) {
301:       PetscCall(PetscInfo(pc, "PCTelescope: generating near nullspace (default)\n"));
302:       PetscCall(PCTelescopeSubNullSpaceCreate_Telescope(pc, sred, nearnullspace, &sub_nearnullspace));
303:       if (PCTelescope_isActiveRank(sred)) {
304:         PetscCall(MatSetNearNullSpace(sub_mat, sub_nearnullspace));
305:         PetscCall(MatNullSpaceDestroy(&sub_nearnullspace));
306:       }
307:     }
308:   }
309:   PetscFunctionReturn(PETSC_SUCCESS);
310: }

312: static PetscErrorCode PCView_Telescope(PC pc, PetscViewer viewer)
313: {
314:   PC_Telescope sred = (PC_Telescope)pc->data;
315:   PetscBool    isascii, isstring;
316:   PetscViewer  subviewer;

318:   PetscFunctionBegin;
319:   PetscCall(PetscObjectTypeCompare((PetscObject)viewer, PETSCVIEWERASCII, &isascii));
320:   PetscCall(PetscObjectTypeCompare((PetscObject)viewer, PETSCVIEWERSTRING, &isstring));
321:   if (isascii) {
322:     {
323:       MPI_Comm    comm, subcomm;
324:       PetscMPIInt comm_size, subcomm_size;
325:       DM          dm = NULL, subdm = NULL;

327:       PetscCall(PCGetDM(pc, &dm));
328:       subdm = private_PCTelescopeGetSubDM(sred);

330:       if (sred->psubcomm) {
331:         comm    = PetscSubcommParent(sred->psubcomm);
332:         subcomm = PetscSubcommChild(sred->psubcomm);
333:         PetscCallMPI(MPI_Comm_size(comm, &comm_size));
334:         PetscCallMPI(MPI_Comm_size(subcomm, &subcomm_size));

336:         PetscCall(PetscViewerASCIIPushTab(viewer));
337:         PetscCall(PetscViewerASCIIPrintf(viewer, "PETSc subcomm: parent comm size reduction factor = %" PetscInt_FMT "\n", sred->redfactor));
338:         PetscCall(PetscViewerASCIIPrintf(viewer, "PETSc subcomm: parent_size = %d , subcomm_size = %d\n", comm_size, subcomm_size));
339:         switch (sred->subcommtype) {
340:         case PETSC_SUBCOMM_INTERLACED:
341:           PetscCall(PetscViewerASCIIPrintf(viewer, "PETSc subcomm: type = %s\n", PetscSubcommTypes[sred->subcommtype]));
342:           break;
343:         case PETSC_SUBCOMM_CONTIGUOUS:
344:           PetscCall(PetscViewerASCIIPrintf(viewer, "PETSc subcomm type = %s\n", PetscSubcommTypes[sred->subcommtype]));
345:           break;
346:         default:
347:           SETERRQ(PetscObjectComm((PetscObject)pc), PETSC_ERR_SUP, "General subcomm type not supported by PCTelescope");
348:         }
349:         PetscCall(PetscViewerASCIIPopTab(viewer));
350:       } else {
351:         PetscCall(PetscObjectGetComm((PetscObject)pc, &comm));
352:         subcomm = sred->subcomm;
353:         if (!PCTelescope_isActiveRank(sred)) subcomm = PETSC_COMM_SELF;

355:         PetscCall(PetscViewerASCIIPushTab(viewer));
356:         PetscCall(PetscViewerASCIIPrintf(viewer, "subcomm: using user provided sub-communicator\n"));
357:         PetscCall(PetscViewerASCIIPopTab(viewer));
358:       }

360:       PetscCall(PetscViewerGetSubViewer(viewer, subcomm, &subviewer));
361:       if (PCTelescope_isActiveRank(sred)) {
362:         PetscCall(PetscViewerASCIIPushTab(subviewer));

364:         if (dm && sred->ignore_dm) PetscCall(PetscViewerASCIIPrintf(subviewer, "ignoring DM\n"));
365:         if (sred->ignore_kspcomputeoperators) PetscCall(PetscViewerASCIIPrintf(subviewer, "ignoring KSPComputeOperators\n"));
366:         switch (sred->sr_type) {
367:         case TELESCOPE_DEFAULT:
368:           PetscCall(PetscViewerASCIIPrintf(subviewer, "setup type: default\n"));
369:           break;
370:         case TELESCOPE_DMDA:
371:           PetscCall(PetscViewerASCIIPrintf(subviewer, "setup type: DMDA auto-repartitioning\n"));
372:           PetscCall(DMView_DA_Short(subdm, subviewer));
373:           break;
374:         case TELESCOPE_DMPLEX:
375:           PetscCall(PetscViewerASCIIPrintf(subviewer, "setup type: DMPLEX auto-repartitioning\n"));
376:           break;
377:         case TELESCOPE_COARSEDM:
378:           PetscCall(PetscViewerASCIIPrintf(subviewer, "setup type: coarse DM\n"));
379:           break;
380:         }

382:         if (dm) {
383:           PetscObject obj = (PetscObject)dm;
384:           PetscCall(PetscViewerASCIIPrintf(subviewer, "Parent DM object:"));
385:           PetscCall(PetscViewerASCIIUseTabs(subviewer, PETSC_FALSE));
386:           if (obj->type_name) PetscCall(PetscViewerASCIIPrintf(subviewer, " type = %s;", obj->type_name));
387:           if (obj->name) PetscCall(PetscViewerASCIIPrintf(subviewer, " name = %s;", obj->name));
388:           if (obj->prefix) PetscCall(PetscViewerASCIIPrintf(subviewer, " prefix = %s", obj->prefix));
389:           PetscCall(PetscViewerASCIIPrintf(subviewer, "\n"));
390:           PetscCall(PetscViewerASCIIUseTabs(subviewer, PETSC_TRUE));
391:         } else {
392:           PetscCall(PetscViewerASCIIPrintf(subviewer, "Parent DM object: NULL\n"));
393:         }
394:         if (subdm) {
395:           PetscObject obj = (PetscObject)subdm;
396:           PetscCall(PetscViewerASCIIPrintf(subviewer, "Sub DM object:"));
397:           PetscCall(PetscViewerASCIIUseTabs(subviewer, PETSC_FALSE));
398:           if (obj->type_name) PetscCall(PetscViewerASCIIPrintf(subviewer, " type = %s;", obj->type_name));
399:           if (obj->name) PetscCall(PetscViewerASCIIPrintf(subviewer, " name = %s;", obj->name));
400:           if (obj->prefix) PetscCall(PetscViewerASCIIPrintf(subviewer, " prefix = %s", obj->prefix));
401:           PetscCall(PetscViewerASCIIPrintf(subviewer, "\n"));
402:           PetscCall(PetscViewerASCIIUseTabs(subviewer, PETSC_TRUE));
403:         } else {
404:           PetscCall(PetscViewerASCIIPrintf(subviewer, "Sub DM object: NULL\n"));
405:         }

407:         PetscCall(KSPView(sred->ksp, subviewer));
408:         PetscCall(PetscViewerASCIIPopTab(subviewer));
409:       }
410:       PetscCall(PetscViewerRestoreSubViewer(viewer, subcomm, &subviewer));
411:     }
412:   }
413:   PetscFunctionReturn(PETSC_SUCCESS);
414: }

416: static PetscErrorCode PCSetUp_Telescope(PC pc)
417: {
418:   PC_Telescope    sred = (PC_Telescope)pc->data;
419:   MPI_Comm        comm, subcomm = 0;
420:   PCTelescopeType sr_type;

422:   PetscFunctionBegin;
423:   PetscCall(PetscObjectGetComm((PetscObject)pc, &comm));

425:   /* Determine type of setup/update */
426:   if (!pc->setupcalled) {
427:     PetscBool has_dm, same;
428:     DM        dm;

430:     sr_type = TELESCOPE_DEFAULT;
431:     has_dm  = PETSC_FALSE;
432:     PetscCall(PCGetDM(pc, &dm));
433:     if (dm) has_dm = PETSC_TRUE;
434:     if (has_dm) {
435:       /* check for dmda */
436:       PetscCall(PetscObjectTypeCompare((PetscObject)dm, DMDA, &same));
437:       if (same) {
438:         PetscCall(PetscInfo(pc, "PCTelescope: found DMDA\n"));
439:         sr_type = TELESCOPE_DMDA;
440:       }
441:       /* check for dmplex */
442:       PetscCall(PetscObjectTypeCompare((PetscObject)dm, DMPLEX, &same));
443:       if (same) {
444:         PetscCall(PetscInfo(pc, "PCTelescope: found DMPLEX\n"));
445:         sr_type = TELESCOPE_DMPLEX;
446:       }

448:       if (sred->use_coarse_dm) {
449:         PetscCall(PetscInfo(pc, "PCTelescope: using coarse DM\n"));
450:         sr_type = TELESCOPE_COARSEDM;
451:       }

453:       if (sred->ignore_dm) {
454:         PetscCall(PetscInfo(pc, "PCTelescope: ignoring DM\n"));
455:         sr_type = TELESCOPE_DEFAULT;
456:       }
457:     }
458:     sred->sr_type = sr_type;
459:   } else {
460:     sr_type = sred->sr_type;
461:   }

463:   /* set function pointers for repartition setup, matrix creation/update, matrix (near) nullspace, and reset functionality */
464:   switch (sr_type) {
465:   case TELESCOPE_DEFAULT:
466:     sred->pctelescope_setup_type              = PCTelescopeSetUp_default;
467:     sred->pctelescope_matcreate_type          = PCTelescopeMatCreate_default;
468:     sred->pctelescope_matnullspacecreate_type = PCTelescopeMatNullSpaceCreate_default;
469:     sred->pctelescope_reset_type              = NULL;
470:     break;
471:   case TELESCOPE_DMDA:
472:     pc->ops->apply                            = PCApply_Telescope_dmda;
473:     pc->ops->applyrichardson                  = PCApplyRichardson_Telescope_dmda;
474:     sred->pctelescope_setup_type              = PCTelescopeSetUp_dmda;
475:     sred->pctelescope_matcreate_type          = PCTelescopeMatCreate_dmda;
476:     sred->pctelescope_matnullspacecreate_type = PCTelescopeMatNullSpaceCreate_dmda;
477:     sred->pctelescope_reset_type              = PCReset_Telescope_dmda;
478:     break;
479:   case TELESCOPE_DMPLEX:
480:     SETERRQ(comm, PETSC_ERR_SUP, "Support for DMPLEX is currently not available");
481:   case TELESCOPE_COARSEDM:
482:     pc->ops->apply                            = PCApply_Telescope_CoarseDM;
483:     pc->ops->applyrichardson                  = PCApplyRichardson_Telescope_CoarseDM;
484:     sred->pctelescope_setup_type              = PCTelescopeSetUp_CoarseDM;
485:     sred->pctelescope_matcreate_type          = NULL;
486:     sred->pctelescope_matnullspacecreate_type = NULL; /* PCTelescopeMatNullSpaceCreate_CoarseDM; */
487:     sred->pctelescope_reset_type              = PCReset_Telescope_CoarseDM;
488:     break;
489:   default:
490:     SETERRQ(comm, PETSC_ERR_SUP, "Support only provided for: repartitioning an operator; repartitioning a DMDA; or using a coarse DM");
491:   }

493:   /* subcomm definition */
494:   if (!pc->setupcalled) {
495:     if ((sr_type == TELESCOPE_DEFAULT) || (sr_type == TELESCOPE_DMDA)) {
496:       if (!sred->psubcomm) {
497:         PetscCall(PetscSubcommCreate(comm, &sred->psubcomm));
498:         PetscCall(PetscSubcommSetNumber(sred->psubcomm, sred->redfactor));
499:         PetscCall(PetscSubcommSetType(sred->psubcomm, sred->subcommtype));
500:         sred->subcomm = PetscSubcommChild(sred->psubcomm);
501:       }
502:     } else { /* query PC for DM, check communicators */
503:       DM          dm, dm_coarse_partition          = NULL;
504:       MPI_Comm    comm_fine, comm_coarse_partition = MPI_COMM_NULL;
505:       PetscMPIInt csize_fine = 0, csize_coarse_partition = 0, cs[2], csg[2], cnt = 0;
506:       PetscBool   isvalidsubcomm = PETSC_TRUE;

508:       PetscCall(PCGetDM(pc, &dm));
509:       comm_fine = PetscObjectComm((PetscObject)dm);
510:       PetscCall(DMGetCoarseDM(dm, &dm_coarse_partition));
511:       if (dm_coarse_partition) cnt = 1;
512:       PetscCallMPI(MPIU_Allreduce(MPI_IN_PLACE, &cnt, 1, MPI_INT, MPI_SUM, comm_fine));
513:       PetscCheck(cnt != 0, comm_fine, PETSC_ERR_SUP, "Zero instances of a coarse DM were found");

515:       PetscCallMPI(MPI_Comm_size(comm_fine, &csize_fine));
516:       if (dm_coarse_partition) {
517:         comm_coarse_partition = PetscObjectComm((PetscObject)dm_coarse_partition);
518:         PetscCallMPI(MPI_Comm_size(comm_coarse_partition, &csize_coarse_partition));
519:       }

521:       cs[0] = csize_fine;
522:       cs[1] = csize_coarse_partition;
523:       PetscCallMPI(MPIU_Allreduce(cs, csg, 2, MPI_INT, MPI_MAX, comm_fine));
524:       PetscCheck(csg[0] != csg[1], comm_fine, PETSC_ERR_SUP, "Coarse DM uses the same size communicator as the parent DM attached to the PC");

526:       PetscCall(PCTelescopeTestValidSubcomm(comm_fine, comm_coarse_partition, &isvalidsubcomm));
527:       PetscCheck(isvalidsubcomm, comm_fine, PETSC_ERR_SUP, "Coarse DM communicator is not a sub-communicator of parentDM->comm");
528:       sred->subcomm = comm_coarse_partition;
529:     }
530:   }
531:   subcomm = sred->subcomm;

533:   /* internal KSP */
534:   if (!pc->setupcalled) {
535:     const char *prefix;

537:     if (PCTelescope_isActiveRank(sred)) {
538:       PetscCall(KSPCreate(subcomm, &sred->ksp));
539:       PetscCall(KSPSetNestLevel(sred->ksp, pc->kspnestlevel));
540:       PetscCall(KSPSetErrorIfNotConverged(sred->ksp, pc->erroriffailure));
541:       PetscCall(PetscObjectIncrementTabLevel((PetscObject)sred->ksp, (PetscObject)pc, 1));
542:       PetscCall(KSPSetType(sred->ksp, KSPPREONLY));
543:       PetscCall(PCGetOptionsPrefix(pc, &prefix));
544:       PetscCall(KSPSetOptionsPrefix(sred->ksp, prefix));
545:       PetscCall(KSPAppendOptionsPrefix(sred->ksp, "telescope_"));
546:     }
547:   }

549:   /* setup */
550:   if (!pc->setupcalled && sred->pctelescope_setup_type) PetscCall(sred->pctelescope_setup_type(pc, sred));
551:   /* update */
552:   if (!pc->setupcalled) {
553:     if (sred->pctelescope_matcreate_type) PetscCall(sred->pctelescope_matcreate_type(pc, sred, MAT_INITIAL_MATRIX, &sred->Bred));
554:     if (sred->pctelescope_matnullspacecreate_type) PetscCall(sred->pctelescope_matnullspacecreate_type(pc, sred, sred->Bred));
555:   } else {
556:     if (sred->pctelescope_matcreate_type) PetscCall(sred->pctelescope_matcreate_type(pc, sred, MAT_REUSE_MATRIX, &sred->Bred));
557:   }

559:   /* common - no construction */
560:   if (PCTelescope_isActiveRank(sred)) {
561:     PetscCall(KSPSetOperators(sred->ksp, sred->Bred, sred->Bred));
562:     if (pc->setfromoptionscalled && !pc->setupcalled) PetscCall(KSPSetFromOptions(sred->ksp));
563:   }
564:   PetscFunctionReturn(PETSC_SUCCESS);
565: }

567: static PetscErrorCode PCApply_Telescope(PC pc, Vec x, Vec y)
568: {
569:   PC_Telescope       sred = (PC_Telescope)pc->data;
570:   Vec                xtmp, xred, yred;
571:   PetscInt           i, st, ed;
572:   VecScatter         scatter;
573:   PetscScalar       *array;
574:   const PetscScalar *x_array;

576:   PetscFunctionBegin;
577:   PetscCall(PetscCitationsRegister(citation, &cited));

579:   xtmp    = sred->xtmp;
580:   scatter = sred->scatter;
581:   xred    = sred->xred;
582:   yred    = sred->yred;

584:   /* pull in vector x->xtmp */
585:   PetscCall(VecScatterBegin(scatter, x, xtmp, INSERT_VALUES, SCATTER_FORWARD));
586:   PetscCall(VecScatterEnd(scatter, x, xtmp, INSERT_VALUES, SCATTER_FORWARD));

588:   /* copy vector entries into xred */
589:   PetscCall(VecGetArrayRead(xtmp, &x_array));
590:   if (xred) {
591:     PetscScalar *LA_xred;
592:     PetscCall(VecGetOwnershipRange(xred, &st, &ed));
593:     PetscCall(VecGetArray(xred, &LA_xred));
594:     for (i = 0; i < ed - st; i++) LA_xred[i] = x_array[i];
595:     PetscCall(VecRestoreArray(xred, &LA_xred));
596:   }
597:   PetscCall(VecRestoreArrayRead(xtmp, &x_array));
598:   /* solve */
599:   if (PCTelescope_isActiveRank(sred)) {
600:     PetscCall(KSPSolve(sred->ksp, xred, yred));
601:     PetscCall(KSPCheckSolve(sred->ksp, pc, yred));
602:   }
603:   /* return vector */
604:   PetscCall(VecGetArray(xtmp, &array));
605:   if (yred) {
606:     const PetscScalar *LA_yred;
607:     PetscCall(VecGetOwnershipRange(yred, &st, &ed));
608:     PetscCall(VecGetArrayRead(yred, &LA_yred));
609:     for (i = 0; i < ed - st; i++) array[i] = LA_yred[i];
610:     PetscCall(VecRestoreArrayRead(yred, &LA_yred));
611:   }
612:   PetscCall(VecRestoreArray(xtmp, &array));
613:   PetscCall(VecScatterBegin(scatter, xtmp, y, INSERT_VALUES, SCATTER_REVERSE));
614:   PetscCall(VecScatterEnd(scatter, xtmp, y, INSERT_VALUES, SCATTER_REVERSE));
615:   PetscFunctionReturn(PETSC_SUCCESS);
616: }

618: static PetscErrorCode PCApplyRichardson_Telescope(PC pc, Vec x, Vec y, Vec w, PetscReal rtol, PetscReal abstol, PetscReal dtol, PetscInt its, PetscBool zeroguess, PetscInt *outits, PCRichardsonConvergedReason *reason)
619: {
620:   PC_Telescope       sred = (PC_Telescope)pc->data;
621:   Vec                xtmp, yred;
622:   PetscInt           i, st, ed;
623:   VecScatter         scatter;
624:   const PetscScalar *x_array;
625:   PetscBool          default_init_guess_value;

627:   PetscFunctionBegin;
628:   xtmp    = sred->xtmp;
629:   scatter = sred->scatter;
630:   yred    = sred->yred;

632:   PetscCheck(its <= 1, PetscObjectComm((PetscObject)pc), PETSC_ERR_SUP, "PCApplyRichardson_Telescope only supports max_it = 1");
633:   *reason = (PCRichardsonConvergedReason)0;

635:   if (!zeroguess) {
636:     PetscCall(PetscInfo(pc, "PCTelescope: Scattering y for non-zero initial guess\n"));
637:     /* pull in vector y->xtmp */
638:     PetscCall(VecScatterBegin(scatter, y, xtmp, INSERT_VALUES, SCATTER_FORWARD));
639:     PetscCall(VecScatterEnd(scatter, y, xtmp, INSERT_VALUES, SCATTER_FORWARD));

641:     /* copy vector entries into xred */
642:     PetscCall(VecGetArrayRead(xtmp, &x_array));
643:     if (yred) {
644:       PetscScalar *LA_yred;
645:       PetscCall(VecGetOwnershipRange(yred, &st, &ed));
646:       PetscCall(VecGetArray(yred, &LA_yred));
647:       for (i = 0; i < ed - st; i++) LA_yred[i] = x_array[i];
648:       PetscCall(VecRestoreArray(yred, &LA_yred));
649:     }
650:     PetscCall(VecRestoreArrayRead(xtmp, &x_array));
651:   }

653:   if (PCTelescope_isActiveRank(sred)) {
654:     PetscCall(KSPGetInitialGuessNonzero(sred->ksp, &default_init_guess_value));
655:     if (!zeroguess) PetscCall(KSPSetInitialGuessNonzero(sred->ksp, PETSC_TRUE));
656:   }

658:   PetscCall(PCApply_Telescope(pc, x, y));

660:   if (PCTelescope_isActiveRank(sred)) PetscCall(KSPSetInitialGuessNonzero(sred->ksp, default_init_guess_value));

662:   if (!*reason) *reason = PCRICHARDSON_CONVERGED_ITS;
663:   *outits = 1;
664:   PetscFunctionReturn(PETSC_SUCCESS);
665: }

667: static PetscErrorCode PCReset_Telescope(PC pc)
668: {
669:   PC_Telescope sred = (PC_Telescope)pc->data;

671:   PetscFunctionBegin;
672:   PetscCall(ISDestroy(&sred->isin));
673:   PetscCall(VecScatterDestroy(&sred->scatter));
674:   PetscCall(VecDestroy(&sred->xred));
675:   PetscCall(VecDestroy(&sred->yred));
676:   PetscCall(VecDestroy(&sred->xtmp));
677:   PetscCall(MatDestroy(&sred->Bred));
678:   PetscCall(KSPReset(sred->ksp));
679:   if (sred->pctelescope_reset_type) PetscCall(sred->pctelescope_reset_type(pc));
680:   PetscFunctionReturn(PETSC_SUCCESS);
681: }

683: static PetscErrorCode PCDestroy_Telescope(PC pc)
684: {
685:   PC_Telescope sred = (PC_Telescope)pc->data;

687:   PetscFunctionBegin;
688:   PetscCall(PCReset_Telescope(pc));
689:   PetscCall(KSPDestroy(&sred->ksp));
690:   PetscCall(PetscSubcommDestroy(&sred->psubcomm));
691:   PetscCall(PetscFree(sred->dm_ctx));
692:   PetscCall(PetscObjectComposeFunction((PetscObject)pc, "PCTelescopeGetKSP_C", NULL));
693:   PetscCall(PetscObjectComposeFunction((PetscObject)pc, "PCTelescopeGetSubcommType_C", NULL));
694:   PetscCall(PetscObjectComposeFunction((PetscObject)pc, "PCTelescopeSetSubcommType_C", NULL));
695:   PetscCall(PetscObjectComposeFunction((PetscObject)pc, "PCTelescopeGetReductionFactor_C", NULL));
696:   PetscCall(PetscObjectComposeFunction((PetscObject)pc, "PCTelescopeSetReductionFactor_C", NULL));
697:   PetscCall(PetscObjectComposeFunction((PetscObject)pc, "PCTelescopeGetIgnoreDM_C", NULL));
698:   PetscCall(PetscObjectComposeFunction((PetscObject)pc, "PCTelescopeSetIgnoreDM_C", NULL));
699:   PetscCall(PetscObjectComposeFunction((PetscObject)pc, "PCTelescopeGetIgnoreKSPComputeOperators_C", NULL));
700:   PetscCall(PetscObjectComposeFunction((PetscObject)pc, "PCTelescopeSetIgnoreKSPComputeOperators_C", NULL));
701:   PetscCall(PetscObjectComposeFunction((PetscObject)pc, "PCTelescopeGetDM_C", NULL));
702:   PetscCall(PetscObjectComposeFunction((PetscObject)pc, "PCTelescopeGetUseCoarseDM_C", NULL));
703:   PetscCall(PetscObjectComposeFunction((PetscObject)pc, "PCTelescopeSetUseCoarseDM_C", NULL));
704:   PetscCall(PetscFree(pc->data));
705:   PetscFunctionReturn(PETSC_SUCCESS);
706: }

708: static PetscErrorCode PCSetFromOptions_Telescope(PC pc, PetscOptionItems PetscOptionsObject)
709: {
710:   PC_Telescope     sred = (PC_Telescope)pc->data;
711:   MPI_Comm         comm;
712:   PetscMPIInt      size;
713:   PetscBool        flg;
714:   PetscSubcommType subcommtype;

716:   PetscFunctionBegin;
717:   PetscCall(PetscObjectGetComm((PetscObject)pc, &comm));
718:   PetscCallMPI(MPI_Comm_size(comm, &size));
719:   PetscOptionsHeadBegin(PetscOptionsObject, "Telescope options");
720:   PetscCall(PetscOptionsEnum("-pc_telescope_subcomm_type", "Subcomm type (interlaced or contiguous)", "PCTelescopeSetSubcommType", PetscSubcommTypes, (PetscEnum)sred->subcommtype, (PetscEnum *)&subcommtype, &flg));
721:   if (flg) PetscCall(PCTelescopeSetSubcommType(pc, subcommtype));
722:   PetscCall(PetscOptionsInt("-pc_telescope_reduction_factor", "Factor to reduce comm size by", "PCTelescopeSetReductionFactor", sred->redfactor, &sred->redfactor, NULL));
723:   PetscCheck(sred->redfactor <= size, comm, PETSC_ERR_ARG_WRONG, "-pc_telescope_reduction_factor <= comm size");
724:   PetscCall(PetscOptionsBool("-pc_telescope_ignore_dm", "Ignore any DM attached to the PC", "PCTelescopeSetIgnoreDM", sred->ignore_dm, &sred->ignore_dm, NULL));
725:   PetscCall(PetscOptionsBool("-pc_telescope_ignore_kspcomputeoperators", "Ignore method used to compute A", "PCTelescopeSetIgnoreKSPComputeOperators", sred->ignore_kspcomputeoperators, &sred->ignore_kspcomputeoperators, NULL));
726:   PetscCall(PetscOptionsBool("-pc_telescope_use_coarse_dm", "Define sub-communicator from the coarse DM", "PCTelescopeSetUseCoarseDM", sred->use_coarse_dm, &sred->use_coarse_dm, NULL));
727:   PetscOptionsHeadEnd();
728:   PetscFunctionReturn(PETSC_SUCCESS);
729: }

731: /* PC implementation specific API's */

733: static PetscErrorCode PCTelescopeGetKSP_Telescope(PC pc, KSP *ksp)
734: {
735:   PC_Telescope red = (PC_Telescope)pc->data;

737:   PetscFunctionBegin;
738:   if (ksp) *ksp = red->ksp;
739:   PetscFunctionReturn(PETSC_SUCCESS);
740: }

742: static PetscErrorCode PCTelescopeGetSubcommType_Telescope(PC pc, PetscSubcommType *subcommtype)
743: {
744:   PC_Telescope red = (PC_Telescope)pc->data;

746:   PetscFunctionBegin;
747:   if (subcommtype) *subcommtype = red->subcommtype;
748:   PetscFunctionReturn(PETSC_SUCCESS);
749: }

751: static PetscErrorCode PCTelescopeSetSubcommType_Telescope(PC pc, PetscSubcommType subcommtype)
752: {
753:   PC_Telescope red = (PC_Telescope)pc->data;

755:   PetscFunctionBegin;
756:   PetscCheck(!pc->setupcalled, PetscObjectComm((PetscObject)pc), PETSC_ERR_ARG_WRONGSTATE, "You cannot change the subcommunicator type for PCTelescope after it has been set up.");
757:   red->subcommtype = subcommtype;
758:   PetscFunctionReturn(PETSC_SUCCESS);
759: }

761: static PetscErrorCode PCTelescopeGetReductionFactor_Telescope(PC pc, PetscInt *fact)
762: {
763:   PC_Telescope red = (PC_Telescope)pc->data;

765:   PetscFunctionBegin;
766:   if (fact) *fact = red->redfactor;
767:   PetscFunctionReturn(PETSC_SUCCESS);
768: }

770: static PetscErrorCode PCTelescopeSetReductionFactor_Telescope(PC pc, PetscInt fact)
771: {
772:   PC_Telescope red = (PC_Telescope)pc->data;
773:   PetscMPIInt  size;

775:   PetscFunctionBegin;
776:   PetscCallMPI(MPI_Comm_size(PetscObjectComm((PetscObject)pc), &size));
777:   PetscCheck(fact > 0, PetscObjectComm((PetscObject)pc), PETSC_ERR_ARG_WRONG, "Reduction factor of telescoping PC %" PetscInt_FMT " must be positive", fact);
778:   PetscCheck(fact <= size, PetscObjectComm((PetscObject)pc), PETSC_ERR_ARG_WRONG, "Reduction factor of telescoping PC %" PetscInt_FMT " must be <= comm.size", fact);
779:   red->redfactor = fact;
780:   PetscFunctionReturn(PETSC_SUCCESS);
781: }

783: static PetscErrorCode PCTelescopeGetIgnoreDM_Telescope(PC pc, PetscBool *v)
784: {
785:   PC_Telescope red = (PC_Telescope)pc->data;

787:   PetscFunctionBegin;
788:   if (v) *v = red->ignore_dm;
789:   PetscFunctionReturn(PETSC_SUCCESS);
790: }

792: static PetscErrorCode PCTelescopeSetIgnoreDM_Telescope(PC pc, PetscBool v)
793: {
794:   PC_Telescope red = (PC_Telescope)pc->data;

796:   PetscFunctionBegin;
797:   red->ignore_dm = v;
798:   PetscFunctionReturn(PETSC_SUCCESS);
799: }

801: static PetscErrorCode PCTelescopeGetUseCoarseDM_Telescope(PC pc, PetscBool *v)
802: {
803:   PC_Telescope red = (PC_Telescope)pc->data;

805:   PetscFunctionBegin;
806:   if (v) *v = red->use_coarse_dm;
807:   PetscFunctionReturn(PETSC_SUCCESS);
808: }

810: static PetscErrorCode PCTelescopeSetUseCoarseDM_Telescope(PC pc, PetscBool v)
811: {
812:   PC_Telescope red = (PC_Telescope)pc->data;

814:   PetscFunctionBegin;
815:   red->use_coarse_dm = v;
816:   PetscFunctionReturn(PETSC_SUCCESS);
817: }

819: static PetscErrorCode PCTelescopeGetIgnoreKSPComputeOperators_Telescope(PC pc, PetscBool *v)
820: {
821:   PC_Telescope red = (PC_Telescope)pc->data;

823:   PetscFunctionBegin;
824:   if (v) *v = red->ignore_kspcomputeoperators;
825:   PetscFunctionReturn(PETSC_SUCCESS);
826: }

828: static PetscErrorCode PCTelescopeSetIgnoreKSPComputeOperators_Telescope(PC pc, PetscBool v)
829: {
830:   PC_Telescope red = (PC_Telescope)pc->data;

832:   PetscFunctionBegin;
833:   red->ignore_kspcomputeoperators = v;
834:   PetscFunctionReturn(PETSC_SUCCESS);
835: }

837: static PetscErrorCode PCTelescopeGetDM_Telescope(PC pc, DM *dm)
838: {
839:   PC_Telescope red = (PC_Telescope)pc->data;

841:   PetscFunctionBegin;
842:   *dm = private_PCTelescopeGetSubDM(red);
843:   PetscFunctionReturn(PETSC_SUCCESS);
844: }

846: /*@
847:   PCTelescopeGetKSP - Gets the `KSP` created by the telescoping `PC`.

849:   Not Collective

851:   Input Parameter:
852: . pc - the preconditioner context

854:   Output Parameter:
855: . subksp - the `KSP` defined on the smaller set of processes

857:   Level: advanced

859: .seealso: [](ch_ksp), `PC`, `KSP`, `PCTELESCOPE`
860: @*/
861: PetscErrorCode PCTelescopeGetKSP(PC pc, KSP *subksp)
862: {
863:   PetscFunctionBegin;
864:   PetscUseMethod(pc, "PCTelescopeGetKSP_C", (PC, KSP *), (pc, subksp));
865:   PetscFunctionReturn(PETSC_SUCCESS);
866: }

868: /*@
869:   PCTelescopeGetReductionFactor - Gets the factor by which the original number of MPI processes has been reduced by that was set by
870:   `PCTelescopeSetReductionFactor()`

872:   Not Collective

874:   Input Parameter:
875: . pc - the preconditioner context

877:   Output Parameter:
878: . fact - the reduction factor

880:   Level: advanced

882: .seealso: [](ch_ksp), `PC`, `PCTELESCOPE`, `PCTelescopeSetReductionFactor()`
883: @*/
884: PetscErrorCode PCTelescopeGetReductionFactor(PC pc, PetscInt *fact)
885: {
886:   PetscFunctionBegin;
887:   PetscUseMethod(pc, "PCTelescopeGetReductionFactor_C", (PC, PetscInt *), (pc, fact));
888:   PetscFunctionReturn(PETSC_SUCCESS);
889: }

891: /*@
892:   PCTelescopeSetReductionFactor - Sets the factor by which the original number of MPI processes will been reduced by when
893:   constructing the subcommunicator to be used with the `PCTELESCOPE`.

895:   Not Collective

897:   Input Parameter:
898: . pc - the preconditioner context

900:   Output Parameter:
901: . fact - the reduction factor

903:   Level: advanced

905: .seealso: [](ch_ksp), `PCTELESCOPE`, `PCTelescopeGetReductionFactor()`
906: @*/
907: PetscErrorCode PCTelescopeSetReductionFactor(PC pc, PetscInt fact)
908: {
909:   PetscFunctionBegin;
910:   PetscTryMethod(pc, "PCTelescopeSetReductionFactor_C", (PC, PetscInt), (pc, fact));
911:   PetscFunctionReturn(PETSC_SUCCESS);
912: }

914: /*@
915:   PCTelescopeGetIgnoreDM - Get the flag indicating if any `DM` attached to the `PC` will be used in constructing the `PC` on the
916:   reduced number of MPI processes

918:   Not Collective

920:   Input Parameter:
921: . pc - the preconditioner context

923:   Output Parameter:
924: . v - the flag

926:   Level: advanced

928: .seealso: [](ch_ksp), `DM`, `PCTELESCOPE`, `PCTelescopeSetIgnoreDM()`
929: @*/
930: PetscErrorCode PCTelescopeGetIgnoreDM(PC pc, PetscBool *v)
931: {
932:   PetscFunctionBegin;
933:   PetscUseMethod(pc, "PCTelescopeGetIgnoreDM_C", (PC, PetscBool *), (pc, v));
934:   PetscFunctionReturn(PETSC_SUCCESS);
935: }

937: /*@
938:   PCTelescopeSetIgnoreDM - Set a flag to ignore any `DM` attached to the `PC` when constructing the `PC` on the
939:   reduced number of MPI processes

941:   Not Collective

943:   Input Parameter:
944: . pc - the preconditioner context

946:   Output Parameter:
947: . v - Use `PETSC_TRUE` to ignore any `DM`

949:   Level: advanced

951: .seealso: [](ch_ksp), `DM`, `PCTELESCOPE`, `PCTelescopeGetIgnoreDM()`
952: @*/
953: PetscErrorCode PCTelescopeSetIgnoreDM(PC pc, PetscBool v)
954: {
955:   PetscFunctionBegin;
956:   PetscTryMethod(pc, "PCTelescopeSetIgnoreDM_C", (PC, PetscBool), (pc, v));
957:   PetscFunctionReturn(PETSC_SUCCESS);
958: }

960: /*@
961:   PCTelescopeGetUseCoarseDM - Get the flag indicating if the coarse `DM` attached to `DM` associated with the `PC` will be used in constructing
962:   the `PC` on the reduced number of MPI processes

964:   Not Collective

966:   Input Parameter:
967: . pc - the preconditioner context

969:   Output Parameter:
970: . v - the flag

972:   Level: advanced

974: .seealso: [](ch_ksp), `DM`, `PCTELESCOPE`, `PCTelescopeSetIgnoreDM()`, `PCTelescopeSetUseCoarseDM()`
975: @*/
976: PetscErrorCode PCTelescopeGetUseCoarseDM(PC pc, PetscBool *v)
977: {
978:   PetscFunctionBegin;
979:   PetscUseMethod(pc, "PCTelescopeGetUseCoarseDM_C", (PC, PetscBool *), (pc, v));
980:   PetscFunctionReturn(PETSC_SUCCESS);
981: }

983: /*@
984:   PCTelescopeSetUseCoarseDM - Set a flag to query the `DM` attached to the `PC` if it also has a coarse `DM` and utilize that `DM`
985:   in constructing the `PC` on the reduced number of MPI processes

987:   Not Collective

989:   Input Parameter:
990: . pc - the preconditioner context

992:   Output Parameter:
993: . v - Use `PETSC_FALSE` to ignore any coarse `DM`

995:   Level: advanced

997:   Notes:
998:   When you have specified to use a coarse `DM`, the communicator used to create the sub-`KSP` within `PCTELESCOPE`
999:   will be that of the coarse `DM`. Hence the flags `-pc_telescope_reduction_factor` and
1000:   `-pc_telescope_subcomm_type` will not be used.

1002:   It is required that the communicator associated with the parent (fine) and the coarse `DM` are of different sizes.
1003:   An error will occur of the size if the communicator associated with the coarse `DM` is the same as that of the parent `DM`.
1004:   Furthermore, it is required that the communicator on the coarse `DM` is a sub-communicator of the parent.
1005:   This will be checked at the time the preconditioner is setup and an error will occur if
1006:   the coarse `DM` does not define a sub-communicator of that used by the parent `DM`.

1008:   The particular Telescope setup invoked when using a coarse `DM` is agnostic with respect to the type of
1009:   the `DM` used (e.g. it supports `DMSHELL`, `DMPLEX`, etc).

1011:   Support is currently only provided for the case when you are using `KSPSetComputeOperators()`

1013:   The user is required to compose a function with the parent `DM` to facilitate the transfer of fields (`Vec`)
1014:   between the different decompositions defined by the fine and coarse `DM`s.
1015:   In the user code, this is achieved via
1016: .vb
1017:    {
1018:      DM dm_fine;
1019:      PetscObjectCompose((PetscObject)dm_fine,"PCTelescopeFieldScatter",your_field_scatter_method);
1020:    }
1021: .ve
1022:   The signature of the user provided field scatter method is
1023: .vb
1024:    PetscErrorCode your_field_scatter_method(DM dm_fine,Vec x_fine,ScatterMode mode,DM dm_coarse,Vec x_coarse);
1025: .ve
1026:   The user must provide support for both mode `SCATTER_FORWARD` and mode `SCATTER_REVERSE`.
1027:   `SCATTER_FORWARD` implies the direction of transfer is from the parent (fine) `DM` to the coarse `DM`.

1029:   Optionally, the user may also compose a function with the parent `DM` to facilitate the transfer
1030:   of state variables between the fine and coarse `DM`s.
1031:   In the context of a finite element discretization, an example state variable might be
1032:   values associated with quadrature points within each element.
1033:   A user provided state scatter method is composed via
1034: .vb
1035:    {
1036:      DM dm_fine;
1037:      PetscObjectCompose((PetscObject)dm_fine,"PCTelescopeStateScatter",your_state_scatter_method);
1038:    }
1039: .ve
1040:   The signature of the user provided state scatter method is
1041: .vb
1042:    PetscErrorCode your_state_scatter_method(DM dm_fine,ScatterMode mode,DM dm_coarse);
1043: .ve
1044:   `SCATTER_FORWARD` implies the direction of transfer is from the fine `DM` to the coarse `DM`.
1045:   The user is only required to support mode = `SCATTER_FORWARD`.
1046:   No assumption is made about the data type of the state variables.
1047:   These must be managed by the user and must be accessible from the `DM`.

1049:   Care must be taken in defining the user context passed to `KSPSetComputeOperators()` which is to be
1050:   associated with the sub-`KSP` residing within `PCTELESCOPE`.
1051:   In general, `PCTELESCOPE` assumes that the context on the fine and coarse `DM` used with
1052:   `KSPSetComputeOperators()` should be "similar" in type or origin.
1053:   Specifically the following rules are used to infer what context on the sub-`KSP` should be.

1055:   First the contexts from the `KSP` and the fine and coarse `DM`s are retrieved.
1056:   Note that the special case of a `DMSHELL` context is queried.

1058: .vb
1059:    DMKSPGetComputeOperators(dm_fine,&dmfine_kspfunc,&dmfine_kspctx);
1060:    DMGetApplicationContext(dm_fine,&dmfine_appctx);
1061:    DMShellGetContext(dm_fine,&dmfine_shellctx);

1063:    DMGetApplicationContext(dm_coarse,&dmcoarse_appctx);
1064:    DMShellGetContext(dm_coarse,&dmcoarse_shellctx);
1065: .ve

1067:   The following rules are then enforced\:

1069:   1. If `dmfine_kspctx` = `NULL`, then we provide a `NULL` pointer as the context for the sub-`KSP`\:
1070:   `KSPSetComputeOperators`(`sub_ksp`,`dmfine_kspfunc`,`NULL`);

1072:   2. If `dmfine_kspctx` != `NULL` and `dmfine_kspctx` == `dmfine_appctx`,

1074:   check that `dmcoarse_appctx` is also non-`NULL`. If this is true, then\:
1075:   `KSPSetComputeOperators`(`sub_ksp`,`dmfine_kspfunc`,`dmcoarse_appctx`);

1077:   3. If `dmfine_kspctx` != `NULL` and `dmfine_kspctx` == `dmfine_shellctx`,

1079:   check that `dmcoarse_shellctx` is also non-`NULL`. If this is true, then\:
1080:   `KSPSetComputeOperators`(`sub_ksp`,`dmfine_kspfunc`,`dmcoarse_shellctx`);

1082:   If neither of the above three tests passed, then `PCTELESCOPE` cannot safely determine what
1083:   context should be provided to `KSPSetComputeOperators()` for use with the sub-`KSP`.
1084:   In this case, an additional mechanism is provided via a composed function which will return
1085:   the actual context to be used. To use this feature you must compose the "getter" function
1086:   with the coarse `DM`, e.g.
1087: .vb
1088:    {
1089:      DM dm_coarse;
1090:      PetscObjectCompose((PetscObject)dm_coarse,"PCTelescopeGetCoarseDMKSPContext",your_coarse_context_getter);
1091:    }
1092: .ve
1093:   The signature of the user provided method is
1094: .vb
1095:    PetscErrorCode your_coarse_context_getter(DM dm_coarse,void **your_kspcontext);
1096: .ve

1098: .seealso: [](ch_ksp), `DM`, `PCTELESCOPE`, `PCTelescopeSetIgnoreDM()`
1099: @*/
1100: PetscErrorCode PCTelescopeSetUseCoarseDM(PC pc, PetscBool v)
1101: {
1102:   PetscFunctionBegin;
1103:   PetscTryMethod(pc, "PCTelescopeSetUseCoarseDM_C", (PC, PetscBool), (pc, v));
1104:   PetscFunctionReturn(PETSC_SUCCESS);
1105: }

1107: /*@
1108:   PCTelescopeGetIgnoreKSPComputeOperators - Get the flag indicating if `KSPComputeOperators()` will be used to construct
1109:   the matrix on the reduced number of MPI processes

1111:   Not Collective

1113:   Input Parameter:
1114: . pc - the preconditioner context

1116:   Output Parameter:
1117: . v - the flag

1119:   Level: advanced

1121: .seealso: [](ch_ksp), `PCTELESCOPE`, `PCTelescopeSetIgnoreDM()`, `PCTelescopeSetUseCoarseDM()`, `PCTelescopeSetIgnoreKSPComputeOperators()`
1122: @*/
1123: PetscErrorCode PCTelescopeGetIgnoreKSPComputeOperators(PC pc, PetscBool *v)
1124: {
1125:   PetscFunctionBegin;
1126:   PetscUseMethod(pc, "PCTelescopeGetIgnoreKSPComputeOperators_C", (PC, PetscBool *), (pc, v));
1127:   PetscFunctionReturn(PETSC_SUCCESS);
1128: }

1130: /*@
1131:   PCTelescopeSetIgnoreKSPComputeOperators - Set a flag to have `PCTELESCOPE` ignore the function provided to `KSPComputeOperators()` in
1132:   constructint the matrix on the reduced number of MPI processes

1134:   Not Collective

1136:   Input Parameter:
1137: . pc - the preconditioner context

1139:   Output Parameter:
1140: . v - Use `PETSC_TRUE` to ignore the function (if defined) set via `KSPSetComputeOperators()` on `pc`

1142:   Level: advanced

1144: .seealso: [](ch_ksp), `PCTELESCOPE`, `PCTelescopeSetIgnoreDM()`, `PCTelescopeSetUseCoarseDM()`, `PCTelescopeGetIgnoreKSPComputeOperators()`
1145: @*/
1146: PetscErrorCode PCTelescopeSetIgnoreKSPComputeOperators(PC pc, PetscBool v)
1147: {
1148:   PetscFunctionBegin;
1149:   PetscTryMethod(pc, "PCTelescopeSetIgnoreKSPComputeOperators_C", (PC, PetscBool), (pc, v));
1150:   PetscFunctionReturn(PETSC_SUCCESS);
1151: }

1153: /*@
1154:   PCTelescopeGetDM - Get the re-partitioned `DM` attached to the sub-`KSP`.

1156:   Not Collective

1158:   Input Parameter:
1159: . pc - the preconditioner context

1161:   Output Parameter:
1162: . subdm - The re-partitioned `DM`

1164:   Level: advanced

1166: .seealso: [](ch_ksp), `DM`, `PCTELESCOPE`, `PCTelescopeSetIgnoreDM()`, `PCTelescopeSetUseCoarseDM()`, `PCTelescopeGetIgnoreKSPComputeOperators()`
1167: @*/
1168: PetscErrorCode PCTelescopeGetDM(PC pc, DM *subdm)
1169: {
1170:   PetscFunctionBegin;
1171:   PetscUseMethod(pc, "PCTelescopeGetDM_C", (PC, DM *), (pc, subdm));
1172:   PetscFunctionReturn(PETSC_SUCCESS);
1173: }

1175: /*@
1176:   PCTelescopeSetSubcommType - set subcommunicator type `PetscSubcommType` (interlaced or contiguous) to be used when
1177:   the subcommunicator is generated from the given `PC`

1179:   Logically Collective

1181:   Input Parameters:
1182: + pc          - the preconditioner context
1183: - subcommtype - the subcommunicator type (see `PetscSubcommType`)

1185:   Level: advanced

1187: .seealso: [](ch_ksp), `PetscSubcommType`, `PetscSubcomm`, `PCTELESCOPE`, `PCTelescopeGetSubcommType()`
1188: @*/
1189: PetscErrorCode PCTelescopeSetSubcommType(PC pc, PetscSubcommType subcommtype)
1190: {
1191:   PetscFunctionBegin;
1192:   PetscTryMethod(pc, "PCTelescopeSetSubcommType_C", (PC, PetscSubcommType), (pc, subcommtype));
1193:   PetscFunctionReturn(PETSC_SUCCESS);
1194: }

1196: /*@
1197:   PCTelescopeGetSubcommType - Get the subcommunicator type `PetscSubcommType` (interlaced or contiguous) set with `PCTelescopeSetSubcommType()`

1199:   Not Collective

1201:   Input Parameter:
1202: . pc - the preconditioner context

1204:   Output Parameter:
1205: . subcommtype - the subcommunicator type (see `PetscSubcommType`)

1207:   Level: advanced

1209: .seealso: [](ch_ksp), `PetscSubcomm`, `PetscSubcommType`, `PCTELESCOPE`, `PCTelescopeSetSubcommType()`
1210: @*/
1211: PetscErrorCode PCTelescopeGetSubcommType(PC pc, PetscSubcommType *subcommtype)
1212: {
1213:   PetscFunctionBegin;
1214:   PetscUseMethod(pc, "PCTelescopeGetSubcommType_C", (PC, PetscSubcommType *), (pc, subcommtype));
1215:   PetscFunctionReturn(PETSC_SUCCESS);
1216: }

1218: /*MC
1219:    PCTELESCOPE - Runs a `KSP` solver on a sub-communicator {cite}`maysananruppknepleysmith2016` of the communicator used by the original `KSP`.
1220:                  MPI processes not in the sub-communicator are idle during the solve. Usually used to solve the smaller coarser grid problems in multigrid
1221:                  (`PCMG`) that could not be efficiently solved on the entire communication

1223:    Options Database Keys:
1224: +  -pc_telescope_reduction_factor <r>                 - factor to reduce the communicator size by. e.g. with 64 MPI ranks and r=4, the new sub-communicator will have 64/4 = 16 ranks.
1225: .  -pc_telescope_ignore_dm                            - flag to indicate whether an attached `DM` should be ignored in constructing the new `PC`
1226: .  -pc_telescope_subcomm_type <interlaced,contiguous> - defines the selection of MPI processes on the sub-communicator. see `PetscSubcomm` for more information.
1227: .  -pc_telescope_ignore_kspcomputeoperators           - flag to indicate whether `KSPSetComputeOperators()` should be used on the sub-`KSP`.
1228: -  -pc_telescope_use_coarse_dm                        - flag to indicate whether the coarse `DM` should be used to define the sub-communicator.

1230:    Level: advanced

1232:    Notes:
1233:    Assuming that the parent preconditioner `PC` is defined on a communicator c, this implementation
1234:    creates a child sub-communicator (c') containing fewer MPI processes than the original parent preconditioner `PC`.
1235:    The preconditioner is deemed telescopic as it only calls `KSPSolve()` on a single
1236:    sub-communicator, in contrast with `PCREDUNDANT` which calls `KSPSolve()` on N sub-communicators.
1237:    This means there will be MPI processes which will be idle during the application of this preconditioner.
1238:    Additionally, in comparison with `PCREDUNDANT`, `PCTELESCOPE` can utilize an attached `DM` to construct `DM` dependent preconditioner, such as `PCMG`

1240:    The default type `KSPType` of the sub `KSP` (the `KSP` defined on c') is `KSPPREONLY`.

1242:    There are three setup mechanisms for `PCTELESCOPE`. Features support by each type are described below.
1243:    In the following, we will refer to the operators B and B', these are the `Bmat` provided to the `KSP` on the
1244:    communicators c and c' respectively.

1246:    [1] Default setup
1247:    The sub-communicator c' is created via `PetscSubcommCreate()`.
1248:    Any explicitly defined nullspace and near nullspace vectors attached to B with `MatSetNullSpace()` and `MatSetNearNullSpace()` are transferred to B'.
1249:    Currently there is no support for nullspaces provided with `MatNullSpaceSetFunction()`).
1250:    No support is provided for `KSPSetComputeOperators()`.
1251:    Currently there is no support for the flag `-pc_use_amat`.

1253:    [2] `DM` aware setup
1254:    The sub-communicator c' is created via `PetscSubcommCreate()`.
1255:    If a `DM` is attached to the `PC`, it is re-partitioned on the sub-communicator c'.
1256:    Both the `Bmat` operator and the right-hand side vector are permuted into the new DOF ordering defined by the re-partitioned `DM`.
1257:    Currently only support for re-partitioning a `DMDA` is provided.
1258:    Any explicitly defined nullspace or near nullspace vectors attached to the original B with `MatSetNullSpace()`
1259:    and `MatSetNearNullSpace()` are extracted, re-partitioned and set on B'
1260:    (currently there is no support for nullspaces provided with `MatNullSpaceSetFunction()`).
1261:    Support is provided for `KSPSetComputeOperators()`. The user provided function and context is propagated to the sub `KSP`.
1262:    This is fragile since the user must ensure that their user context is valid for use on c'.
1263:    Currently there is no support for the flag `-pc_use_amat`.

1265:    [3] Coarse `DM` setup
1266:    If a `DM` (dmfine) is attached to the `PC`, dmfine is queried for a "coarse" `DM` (call this dmcoarse) via `DMGetCoarseDM()`.
1267:    `PCTELESCOPE` will interpret the coarse `DM` as being defined on a sub-communicator of c.
1268:    The communicator associated with dmcoarse will define the c' to be used within `PCTELESCOPE`.
1269:    `PCTELESCOPE` will check that c' is in fact a sub-communicator of c. If it is not, an error will be reported.
1270:    The intention of this setup type is that `PCTELESCOPE` will use an existing (e.g. user defined) communicator hierarchy, say as would be
1271:    available with using multi-grid on unstructured meshes.
1272:    This setup will not use the command line options `-pc_telescope_reduction_factor` or `-pc_telescope_subcomm_type`.
1273:    Any explicitly defined nullspace or near nullspace vectors attached to the B are extracted, scattered into the correct ordering consistent
1274:    with dmcoarse and set on B'
1275:    (currently there is no support for nullspaces provided with `MatNullSpaceSetFunction()`).
1276:    There is no general method to permute field orderings, hence only `KSPSetComputeOperators()` is supported.
1277:    The user must use `PetscObjectComposeFunction()` with dmfine to define the method to scatter fields from dmfine to dmcoarse.
1278:    Propagation of the user context for `KSPSetComputeOperators()` on the sub `KSP` is attempted by querying the `DM` contexts associated with
1279:    dmfine and dmcoarse. Alternatively, the user may use `PetscObjectComposeFunction()` with dmcoarse to define a method which will return the appropriate user context for `KSPSetComputeOperators()`.
1280:    Currently there is no support for the flag `-pc_use_amat`.
1281:    This setup can be invoked by the option `-pc_telescope_use_coarse_dm` or by calling `PCTelescopeSetUseCoarseDM`(pc,`PETSC_TRUE`);
1282:    Further information about the user-provided methods required by this setup type are described here `PCTelescopeSetUseCoarseDM()`.

1284:    Developer Notes:
1285:    During `PCSetUp()`, the B operator is scattered onto c'.
1286:    Within `PCApply()`, the RHS vector (x) is scattered into a redundant vector, xred (defined on c').
1287:    Then, `KSPSolve()` is executed on the c' communicator.

1289:    The communicator used within the telescoping preconditioner is defined by a `PetscSubcomm` using the INTERLACED
1290:    creation routine by default (this can be changed with `-pc_telescope_subcomm_type`). We run the sub `KSP` on only
1291:    the ranks within the communicator which have a color equal to zero.

1293:    The telescoping preconditioner is aware of nullspaces and near nullspaces which are attached to the B operator.
1294:    In the case where B has a (near) nullspace attached, the (near) nullspace vectors are extracted from B and mapped into
1295:    a new (near) nullspace, defined on the sub-communicator, which is attached to B' (the B operator which was scattered to c')

1297:    The telescoping preconditioner can re-partition an attached `DM` if it is a `DMDA` (2D or 3D -
1298:    support for 1D `DMDA`s is not provided). If a `DMDA` is found, a topologically equivalent `DMDA` is created on c'
1299:    and this new `DM` is attached the sub `KSP`. The design of telescope is such that it should be possible to extend support
1300:    for re-partitioning other to `DM`'s (e.g. `DMPLEX`). The user can supply a flag to ignore attached DMs.
1301:    Alternatively, user-provided re-partitioned `DM`s can be used via `-pc_telescope_use_coarse_dm`.

1303:    With the default setup mode, B' is defined by fusing rows (in order) associated with MPI processes common to c and c'.

1305:    When a `DMDA` is attached to the parent preconditioner, B' is defined by: (i) performing a symmetric permutation of B
1306:    into the ordering defined by the `DMDA` on c', (ii) extracting the local chunks via `MatCreateSubMatrices()`, (iii) fusing the
1307:    locally (sequential) matrices defined on the ranks common to c and c' into B' using `MatCreateMPIMatConcatenateSeqMat()`

1309:    Limitations/improvements include the following.
1310:    `VecPlaceArray()` could be used within `PCApply()` to improve efficiency and reduce memory usage.
1311:    A unified mechanism to query for user contexts as required by `KSPSetComputeOperators()` and `MatNullSpaceSetFunction()`.

1313:    The symmetric permutation used when a `DMDA` is encountered is performed via explicitly assembling a permutation matrix P,
1314:    and performing P^T.A.P. Possibly it might be more efficient to use `MatPermute()`. We opted to use P^T.A.P as it appears
1315:    `VecPermute()` does not support the use case required here. By computing P, one can permute both the operator and RHS in a
1316:    consistent manner.

1318:    Mapping of vectors (default setup mode) is performed in the following way.
1319:    Suppose the parent communicator size was 4, and we set a reduction factor of 2; this would give a comm size on c' of 2.
1320:    Using the interlaced creation routine, the ranks in c with color = 0 will be rank 0 and 2.
1321:    We perform the scatter to the sub-communicator in the following way.
1322:    [1] Given a vector x defined on communicator c

1324: .vb
1325:    rank(c)  local values of x
1326:    ------- ----------------------------------------
1327:         0   [  0.0,  1.0,  2.0,  3.0,  4.0,  5.0 ]
1328:         1   [  6.0,  7.0,  8.0,  9.0, 10.0, 11.0 ]
1329:         2   [ 12.0, 13.0, 14.0, 15.0, 16.0, 17.0 ]
1330:         3   [ 18.0, 19.0, 20.0, 21.0, 22.0, 23.0 ]
1331: .ve

1333:    scatter into xtmp defined also on comm c, so that we have the following values

1335: .vb
1336:    rank(c)  local values of xtmp
1337:    ------- ----------------------------------------------------------------------------
1338:         0   [  0.0,  1.0,  2.0,  3.0,  4.0,  5.0,  6.0,  7.0,  8.0,  9.0, 10.0, 11.0 ]
1339:         1   [ ]
1340:         2   [ 12.0, 13.0, 14.0, 15.0, 16.0, 17.0, 18.0, 19.0, 20.0, 21.0, 22.0, 23.0 ]
1341:         3   [ ]
1342: .ve

1344:    The entries on rank 1 and 3 (ranks which do not have a color = 0 in c') have no values

1346:    [2] Copy the values from ranks 0, 2 (indices with respect to comm c) into the vector xred which is defined on communicator c'.
1347:    Ranks 0 and 2 are the only ranks in the subcomm which have a color = 0.

1349: .vb
1350:    rank(c')  local values of xred
1351:    -------- ----------------------------------------------------------------------------
1352:          0   [  0.0,  1.0,  2.0,  3.0,  4.0,  5.0,  6.0,  7.0,  8.0,  9.0, 10.0, 11.0 ]
1353:          1   [ 12.0, 13.0, 14.0, 15.0, 16.0, 17.0, 18.0, 19.0, 20.0, 21.0, 22.0, 23.0 ]
1354: .ve

1356:   Contributed by:
1357:   Dave May

1359: .seealso: [](ch_ksp), `PCTelescopeGetKSP()`, `PCTelescopeGetDM()`, `PCTelescopeGetReductionFactor()`, `PCTelescopeSetReductionFactor()`, `PCTelescopeGetIgnoreDM()`, `PCTelescopeSetIgnoreDM()`, `PCREDUNDANT`
1360: M*/
1361: PETSC_EXTERN PetscErrorCode PCCreate_Telescope(PC pc)
1362: {
1363:   struct _PC_Telescope *sred;

1365:   PetscFunctionBegin;
1366:   PetscCall(PetscNew(&sred));
1367:   sred->psubcomm                   = NULL;
1368:   sred->subcommtype                = PETSC_SUBCOMM_INTERLACED;
1369:   sred->subcomm                    = MPI_COMM_NULL;
1370:   sred->redfactor                  = 1;
1371:   sred->ignore_dm                  = PETSC_FALSE;
1372:   sred->ignore_kspcomputeoperators = PETSC_FALSE;
1373:   sred->use_coarse_dm              = PETSC_FALSE;
1374:   pc->data                         = (void *)sred;

1376:   pc->ops->apply           = PCApply_Telescope;
1377:   pc->ops->applytranspose  = NULL;
1378:   pc->ops->applyrichardson = PCApplyRichardson_Telescope;
1379:   pc->ops->setup           = PCSetUp_Telescope;
1380:   pc->ops->destroy         = PCDestroy_Telescope;
1381:   pc->ops->reset           = PCReset_Telescope;
1382:   pc->ops->setfromoptions  = PCSetFromOptions_Telescope;
1383:   pc->ops->view            = PCView_Telescope;

1385:   sred->pctelescope_setup_type              = PCTelescopeSetUp_default;
1386:   sred->pctelescope_matcreate_type          = PCTelescopeMatCreate_default;
1387:   sred->pctelescope_matnullspacecreate_type = PCTelescopeMatNullSpaceCreate_default;
1388:   sred->pctelescope_reset_type              = NULL;

1390:   PetscCall(PetscObjectComposeFunction((PetscObject)pc, "PCTelescopeGetKSP_C", PCTelescopeGetKSP_Telescope));
1391:   PetscCall(PetscObjectComposeFunction((PetscObject)pc, "PCTelescopeGetSubcommType_C", PCTelescopeGetSubcommType_Telescope));
1392:   PetscCall(PetscObjectComposeFunction((PetscObject)pc, "PCTelescopeSetSubcommType_C", PCTelescopeSetSubcommType_Telescope));
1393:   PetscCall(PetscObjectComposeFunction((PetscObject)pc, "PCTelescopeGetReductionFactor_C", PCTelescopeGetReductionFactor_Telescope));
1394:   PetscCall(PetscObjectComposeFunction((PetscObject)pc, "PCTelescopeSetReductionFactor_C", PCTelescopeSetReductionFactor_Telescope));
1395:   PetscCall(PetscObjectComposeFunction((PetscObject)pc, "PCTelescopeGetIgnoreDM_C", PCTelescopeGetIgnoreDM_Telescope));
1396:   PetscCall(PetscObjectComposeFunction((PetscObject)pc, "PCTelescopeSetIgnoreDM_C", PCTelescopeSetIgnoreDM_Telescope));
1397:   PetscCall(PetscObjectComposeFunction((PetscObject)pc, "PCTelescopeGetIgnoreKSPComputeOperators_C", PCTelescopeGetIgnoreKSPComputeOperators_Telescope));
1398:   PetscCall(PetscObjectComposeFunction((PetscObject)pc, "PCTelescopeSetIgnoreKSPComputeOperators_C", PCTelescopeSetIgnoreKSPComputeOperators_Telescope));
1399:   PetscCall(PetscObjectComposeFunction((PetscObject)pc, "PCTelescopeGetDM_C", PCTelescopeGetDM_Telescope));
1400:   PetscCall(PetscObjectComposeFunction((PetscObject)pc, "PCTelescopeGetUseCoarseDM_C", PCTelescopeGetUseCoarseDM_Telescope));
1401:   PetscCall(PetscObjectComposeFunction((PetscObject)pc, "PCTelescopeSetUseCoarseDM_C", PCTelescopeSetUseCoarseDM_Telescope));
1402:   PetscFunctionReturn(PETSC_SUCCESS);
1403: }