xref: /petsc/src/ksp/pc/impls/telescope/telescope_dmda.c (revision d9acb416d05abeed0a33bde3a81aeb2ea0364f6a) 
1 #include <petsc/private/matimpl.h>
2 #include <petsc/private/pcimpl.h>
3 #include <petsc/private/dmimpl.h>
4 #include <petscksp.h> /*I "petscksp.h" I*/
5 #include <petscdm.h>
6 #include <petscdmda.h>
7 
8 #include "../src/ksp/pc/impls/telescope/telescope.h"
9 
10 static PetscBool  cited      = PETSC_FALSE;
11 static const char citation[] = "@inproceedings{MaySananRuppKnepleySmith2016,\n"
12                                "  title     = {Extreme-Scale Multigrid Components within PETSc},\n"
13                                "  author    = {Dave A. May and Patrick Sanan and Karl Rupp and Matthew G. Knepley and Barry F. Smith},\n"
14                                "  booktitle = {Proceedings of the Platform for Advanced Scientific Computing Conference},\n"
15                                "  series    = {PASC '16},\n"
16                                "  isbn      = {978-1-4503-4126-4},\n"
17                                "  location  = {Lausanne, Switzerland},\n"
18                                "  pages     = {5:1--5:12},\n"
19                                "  articleno = {5},\n"
20                                "  numpages  = {12},\n"
21                                "  url       = {https://doi.acm.org/10.1145/2929908.2929913},\n"
22                                "  doi       = {10.1145/2929908.2929913},\n"
23                                "  acmid     = {2929913},\n"
24                                "  publisher = {ACM},\n"
25                                "  address   = {New York, NY, USA},\n"
26                                "  keywords  = {GPU, HPC, agglomeration, coarse-level solver, multigrid, parallel computing, preconditioning},\n"
27                                "  year      = {2016}\n"
28                                "}\n";
29 
30 static PetscErrorCode _DMDADetermineRankFromGlobalIJK(PetscInt dim, PetscInt i, PetscInt j, PetscInt k, PetscInt Mp, PetscInt Np, PetscInt Pp, PetscInt start_i[], PetscInt start_j[], PetscInt start_k[], PetscInt span_i[], PetscInt span_j[], PetscInt span_k[], PetscMPIInt *_pi, PetscMPIInt *_pj, PetscMPIInt *_pk, PetscMPIInt *rank_re)
31 {
32   PetscInt pi, pj, pk, n;
33 
34   PetscFunctionBegin;
35   *rank_re = -1;
36   if (_pi) *_pi = -1;
37   if (_pj) *_pj = -1;
38   if (_pk) *_pk = -1;
39   pi = pj = pk = -1;
40   if (_pi) {
41     for (n = 0; n < Mp; n++) {
42       if ((i >= start_i[n]) && (i < start_i[n] + span_i[n])) {
43         pi = n;
44         break;
45       }
46     }
47     PetscCheck(pi != -1, PETSC_COMM_SELF, PETSC_ERR_USER, "[dmda-ijk] pi cannot be determined : range %" PetscInt_FMT ", val %" PetscInt_FMT, Mp, i);
48     *_pi = pi;
49   }
50 
51   if (_pj) {
52     for (n = 0; n < Np; n++) {
53       if ((j >= start_j[n]) && (j < start_j[n] + span_j[n])) {
54         pj = n;
55         break;
56       }
57     }
58     PetscCheck(pj != -1, PETSC_COMM_SELF, PETSC_ERR_USER, "[dmda-ijk] pj cannot be determined : range %" PetscInt_FMT ", val %" PetscInt_FMT, Np, j);
59     *_pj = pj;
60   }
61 
62   if (_pk) {
63     for (n = 0; n < Pp; n++) {
64       if ((k >= start_k[n]) && (k < start_k[n] + span_k[n])) {
65         pk = n;
66         break;
67       }
68     }
69     PetscCheck(pk != -1, PETSC_COMM_SELF, PETSC_ERR_USER, "[dmda-ijk] pk cannot be determined : range %" PetscInt_FMT ", val %" PetscInt_FMT, Pp, k);
70     *_pk = pk;
71   }
72 
73   switch (dim) {
74   case 1:
75     *rank_re = pi;
76     break;
77   case 2:
78     *rank_re = pi + pj * Mp;
79     break;
80   case 3:
81     *rank_re = pi + pj * Mp + pk * (Mp * Np);
82     break;
83   }
84   PetscFunctionReturn(PETSC_SUCCESS);
85 }
86 
87 static PetscErrorCode _DMDADetermineGlobalS0(PetscInt dim, PetscMPIInt rank_re, PetscInt Mp_re, PetscInt Np_re, PetscInt Pp_re, PetscInt range_i_re[], PetscInt range_j_re[], PetscInt range_k_re[], PetscInt *s0)
88 {
89   PetscInt i, j, k, start_IJK = 0;
90   PetscInt rank_ijk;
91 
92   PetscFunctionBegin;
93   switch (dim) {
94   case 1:
95     for (i = 0; i < Mp_re; i++) {
96       rank_ijk = i;
97       if (rank_ijk < rank_re) start_IJK += range_i_re[i];
98     }
99     break;
100   case 2:
101     for (j = 0; j < Np_re; j++) {
102       for (i = 0; i < Mp_re; i++) {
103         rank_ijk = i + j * Mp_re;
104         if (rank_ijk < rank_re) start_IJK += range_i_re[i] * range_j_re[j];
105       }
106     }
107     break;
108   case 3:
109     for (k = 0; k < Pp_re; k++) {
110       for (j = 0; j < Np_re; j++) {
111         for (i = 0; i < Mp_re; i++) {
112           rank_ijk = i + j * Mp_re + k * Mp_re * Np_re;
113           if (rank_ijk < rank_re) start_IJK += range_i_re[i] * range_j_re[j] * range_k_re[k];
114         }
115       }
116     }
117     break;
118   }
119   *s0 = start_IJK;
120   PetscFunctionReturn(PETSC_SUCCESS);
121 }
122 
123 static PetscErrorCode PCTelescopeSetUp_dmda_repart_coors2d(PC_Telescope sred, DM dm, DM subdm)
124 {
125   DM         cdm;
126   Vec        coor, coor_natural, perm_coors;
127   PetscInt   i, j, si, sj, ni, nj, M, N, Ml, Nl, c, nidx;
128   PetscInt  *fine_indices;
129   IS         is_fine, is_local;
130   VecScatter sctx;
131 
132   PetscFunctionBegin;
133   PetscCall(DMGetCoordinates(dm, &coor));
134   if (!coor) PetscFunctionReturn(PETSC_SUCCESS);
135   if (PCTelescope_isActiveRank(sred)) PetscCall(DMDASetUniformCoordinates(subdm, 0.0, 1.0, 0.0, 1.0, 0.0, 1.0));
136   /* Get the coordinate vector from the distributed array */
137   PetscCall(DMGetCoordinateDM(dm, &cdm));
138   PetscCall(DMDACreateNaturalVector(cdm, &coor_natural));
139 
140   PetscCall(DMDAGlobalToNaturalBegin(cdm, coor, INSERT_VALUES, coor_natural));
141   PetscCall(DMDAGlobalToNaturalEnd(cdm, coor, INSERT_VALUES, coor_natural));
142 
143   /* get indices of the guys I want to grab */
144   PetscCall(DMDAGetInfo(dm, NULL, &M, &N, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL));
145   if (PCTelescope_isActiveRank(sred)) {
146     PetscCall(DMDAGetCorners(subdm, &si, &sj, NULL, &ni, &nj, NULL));
147     Ml = ni;
148     Nl = nj;
149   } else {
150     si = sj = 0;
151     ni = nj = 0;
152     Ml = Nl = 0;
153   }
154 
155   PetscCall(PetscMalloc1(Ml * Nl * 2, &fine_indices));
156   c = 0;
157   if (PCTelescope_isActiveRank(sred)) {
158     for (j = sj; j < sj + nj; j++) {
159       for (i = si; i < si + ni; i++) {
160         nidx                = (i) + (j)*M;
161         fine_indices[c]     = 2 * nidx;
162         fine_indices[c + 1] = 2 * nidx + 1;
163         c                   = c + 2;
164       }
165     }
166     PetscCheck(c == Ml * Nl * 2, PETSC_COMM_SELF, PETSC_ERR_PLIB, "c %" PetscInt_FMT " should equal 2 * Ml %" PetscInt_FMT " * Nl %" PetscInt_FMT, c, Ml, Nl);
167   }
168 
169   /* generate scatter */
170   PetscCall(ISCreateGeneral(PetscObjectComm((PetscObject)dm), Ml * Nl * 2, fine_indices, PETSC_USE_POINTER, &is_fine));
171   PetscCall(ISCreateStride(PETSC_COMM_SELF, Ml * Nl * 2, 0, 1, &is_local));
172 
173   /* scatter */
174   PetscCall(VecCreate(PETSC_COMM_SELF, &perm_coors));
175   PetscCall(VecSetSizes(perm_coors, PETSC_DECIDE, Ml * Nl * 2));
176   PetscCall(VecSetType(perm_coors, VECSEQ));
177 
178   PetscCall(VecScatterCreate(coor_natural, is_fine, perm_coors, is_local, &sctx));
179   PetscCall(VecScatterBegin(sctx, coor_natural, perm_coors, INSERT_VALUES, SCATTER_FORWARD));
180   PetscCall(VecScatterEnd(sctx, coor_natural, perm_coors, INSERT_VALUES, SCATTER_FORWARD));
181   /* access */
182   if (PCTelescope_isActiveRank(sred)) {
183     Vec                _coors;
184     const PetscScalar *LA_perm;
185     PetscScalar       *LA_coors;
186 
187     PetscCall(DMGetCoordinates(subdm, &_coors));
188     PetscCall(VecGetArrayRead(perm_coors, &LA_perm));
189     PetscCall(VecGetArray(_coors, &LA_coors));
190     for (i = 0; i < Ml * Nl * 2; i++) LA_coors[i] = LA_perm[i];
191     PetscCall(VecRestoreArray(_coors, &LA_coors));
192     PetscCall(VecRestoreArrayRead(perm_coors, &LA_perm));
193   }
194 
195   /* update local coords */
196   if (PCTelescope_isActiveRank(sred)) {
197     DM  _dmc;
198     Vec _coors, _coors_local;
199     PetscCall(DMGetCoordinateDM(subdm, &_dmc));
200     PetscCall(DMGetCoordinates(subdm, &_coors));
201     PetscCall(DMGetCoordinatesLocal(subdm, &_coors_local));
202     PetscCall(DMGlobalToLocalBegin(_dmc, _coors, INSERT_VALUES, _coors_local));
203     PetscCall(DMGlobalToLocalEnd(_dmc, _coors, INSERT_VALUES, _coors_local));
204   }
205   PetscCall(VecScatterDestroy(&sctx));
206   PetscCall(ISDestroy(&is_fine));
207   PetscCall(PetscFree(fine_indices));
208   PetscCall(ISDestroy(&is_local));
209   PetscCall(VecDestroy(&perm_coors));
210   PetscCall(VecDestroy(&coor_natural));
211   PetscFunctionReturn(PETSC_SUCCESS);
212 }
213 
214 static PetscErrorCode PCTelescopeSetUp_dmda_repart_coors3d(PC_Telescope sred, DM dm, DM subdm)
215 {
216   DM         cdm;
217   Vec        coor, coor_natural, perm_coors;
218   PetscInt   i, j, k, si, sj, sk, ni, nj, nk, M, N, P, Ml, Nl, Pl, c, nidx;
219   PetscInt  *fine_indices;
220   IS         is_fine, is_local;
221   VecScatter sctx;
222 
223   PetscFunctionBegin;
224   PetscCall(DMGetCoordinates(dm, &coor));
225   if (!coor) PetscFunctionReturn(PETSC_SUCCESS);
226 
227   if (PCTelescope_isActiveRank(sred)) PetscCall(DMDASetUniformCoordinates(subdm, 0.0, 1.0, 0.0, 1.0, 0.0, 1.0));
228 
229   /* Get the coordinate vector from the distributed array */
230   PetscCall(DMGetCoordinateDM(dm, &cdm));
231   PetscCall(DMDACreateNaturalVector(cdm, &coor_natural));
232   PetscCall(DMDAGlobalToNaturalBegin(cdm, coor, INSERT_VALUES, coor_natural));
233   PetscCall(DMDAGlobalToNaturalEnd(cdm, coor, INSERT_VALUES, coor_natural));
234 
235   /* get indices of the guys I want to grab */
236   PetscCall(DMDAGetInfo(dm, NULL, &M, &N, &P, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL));
237 
238   if (PCTelescope_isActiveRank(sred)) {
239     PetscCall(DMDAGetCorners(subdm, &si, &sj, &sk, &ni, &nj, &nk));
240     Ml = ni;
241     Nl = nj;
242     Pl = nk;
243   } else {
244     si = sj = sk = 0;
245     ni = nj = nk = 0;
246     Ml = Nl = Pl = 0;
247   }
248 
249   PetscCall(PetscMalloc1(Ml * Nl * Pl * 3, &fine_indices));
250 
251   c = 0;
252   if (PCTelescope_isActiveRank(sred)) {
253     for (k = sk; k < sk + nk; k++) {
254       for (j = sj; j < sj + nj; j++) {
255         for (i = si; i < si + ni; i++) {
256           nidx                = (i) + (j)*M + (k)*M * N;
257           fine_indices[c]     = 3 * nidx;
258           fine_indices[c + 1] = 3 * nidx + 1;
259           fine_indices[c + 2] = 3 * nidx + 2;
260           c                   = c + 3;
261         }
262       }
263     }
264   }
265 
266   /* generate scatter */
267   PetscCall(ISCreateGeneral(PetscObjectComm((PetscObject)dm), Ml * Nl * Pl * 3, fine_indices, PETSC_USE_POINTER, &is_fine));
268   PetscCall(ISCreateStride(PETSC_COMM_SELF, Ml * Nl * Pl * 3, 0, 1, &is_local));
269 
270   /* scatter */
271   PetscCall(VecCreate(PETSC_COMM_SELF, &perm_coors));
272   PetscCall(VecSetSizes(perm_coors, PETSC_DECIDE, Ml * Nl * Pl * 3));
273   PetscCall(VecSetType(perm_coors, VECSEQ));
274   PetscCall(VecScatterCreate(coor_natural, is_fine, perm_coors, is_local, &sctx));
275   PetscCall(VecScatterBegin(sctx, coor_natural, perm_coors, INSERT_VALUES, SCATTER_FORWARD));
276   PetscCall(VecScatterEnd(sctx, coor_natural, perm_coors, INSERT_VALUES, SCATTER_FORWARD));
277 
278   /* access */
279   if (PCTelescope_isActiveRank(sred)) {
280     Vec                _coors;
281     const PetscScalar *LA_perm;
282     PetscScalar       *LA_coors;
283 
284     PetscCall(DMGetCoordinates(subdm, &_coors));
285     PetscCall(VecGetArrayRead(perm_coors, &LA_perm));
286     PetscCall(VecGetArray(_coors, &LA_coors));
287     for (i = 0; i < Ml * Nl * Pl * 3; i++) LA_coors[i] = LA_perm[i];
288     PetscCall(VecRestoreArray(_coors, &LA_coors));
289     PetscCall(VecRestoreArrayRead(perm_coors, &LA_perm));
290   }
291 
292   /* update local coords */
293   if (PCTelescope_isActiveRank(sred)) {
294     DM  _dmc;
295     Vec _coors, _coors_local;
296 
297     PetscCall(DMGetCoordinateDM(subdm, &_dmc));
298     PetscCall(DMGetCoordinates(subdm, &_coors));
299     PetscCall(DMGetCoordinatesLocal(subdm, &_coors_local));
300     PetscCall(DMGlobalToLocalBegin(_dmc, _coors, INSERT_VALUES, _coors_local));
301     PetscCall(DMGlobalToLocalEnd(_dmc, _coors, INSERT_VALUES, _coors_local));
302   }
303 
304   PetscCall(VecScatterDestroy(&sctx));
305   PetscCall(ISDestroy(&is_fine));
306   PetscCall(PetscFree(fine_indices));
307   PetscCall(ISDestroy(&is_local));
308   PetscCall(VecDestroy(&perm_coors));
309   PetscCall(VecDestroy(&coor_natural));
310   PetscFunctionReturn(PETSC_SUCCESS);
311 }
312 
313 static PetscErrorCode PCTelescopeSetUp_dmda_repart_coors(PC pc, PC_Telescope sred, PC_Telescope_DMDACtx *ctx)
314 {
315   PetscInt     dim;
316   DM           dm, subdm;
317   PetscSubcomm psubcomm;
318   MPI_Comm     comm;
319   Vec          coor;
320 
321   PetscFunctionBegin;
322   PetscCall(PCGetDM(pc, &dm));
323   PetscCall(DMGetCoordinates(dm, &coor));
324   if (!coor) PetscFunctionReturn(PETSC_SUCCESS);
325   psubcomm = sred->psubcomm;
326   comm     = PetscSubcommParent(psubcomm);
327   subdm    = ctx->dmrepart;
328 
329   PetscCall(PetscInfo(pc, "PCTelescope: setting up the coordinates (DMDA)\n"));
330   PetscCall(DMDAGetInfo(dm, &dim, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL));
331   switch (dim) {
332   case 1:
333     SETERRQ(comm, PETSC_ERR_SUP, "Telescope: DMDA (1D) repartitioning not provided");
334   case 2:
335     PetscCall(PCTelescopeSetUp_dmda_repart_coors2d(sred, dm, subdm));
336     break;
337   case 3:
338     PetscCall(PCTelescopeSetUp_dmda_repart_coors3d(sred, dm, subdm));
339     break;
340   }
341   PetscFunctionReturn(PETSC_SUCCESS);
342 }
343 
344 /* setup repartitioned dm */
345 static PetscErrorCode PCTelescopeSetUp_dmda_repart(PC pc, PC_Telescope sred, PC_Telescope_DMDACtx *ctx)
346 {
347   DM                    dm;
348   PetscInt              dim, nx, ny, nz, ndof, nsw, sum, k;
349   DMBoundaryType        bx, by, bz;
350   DMDAStencilType       stencil;
351   const PetscInt       *_range_i_re;
352   const PetscInt       *_range_j_re;
353   const PetscInt       *_range_k_re;
354   DMDAInterpolationType itype;
355   PetscInt              refine_x, refine_y, refine_z;
356   MPI_Comm              comm, subcomm;
357   const char           *prefix;
358 
359   PetscFunctionBegin;
360   comm    = PetscSubcommParent(sred->psubcomm);
361   subcomm = PetscSubcommChild(sred->psubcomm);
362   PetscCall(PCGetDM(pc, &dm));
363 
364   PetscCall(DMDAGetInfo(dm, &dim, &nx, &ny, &nz, NULL, NULL, NULL, &ndof, &nsw, &bx, &by, &bz, &stencil));
365   PetscCall(DMDAGetInterpolationType(dm, &itype));
366   PetscCall(DMDAGetRefinementFactor(dm, &refine_x, &refine_y, &refine_z));
367 
368   ctx->dmrepart = NULL;
369   _range_i_re = _range_j_re = _range_k_re = NULL;
370   /* Create DMDA on the child communicator */
371   if (PCTelescope_isActiveRank(sred)) {
372     switch (dim) {
373     case 1:
374       PetscCall(PetscInfo(pc, "PCTelescope: setting up the DMDA on comm subset (1D)\n"));
375       /* PetscCall(DMDACreate1d(subcomm,bx,nx,ndof,nsw,NULL,&ctx->dmrepart)); */
376       ny = nz = 1;
377       by = bz = DM_BOUNDARY_NONE;
378       break;
379     case 2:
380       PetscCall(PetscInfo(pc, "PCTelescope: setting up the DMDA on comm subset (2D)\n"));
381       /* PetscCall(DMDACreate2d(subcomm,bx,by,stencil,nx,ny, PETSC_DECIDE,PETSC_DECIDE,
382          ndof,nsw, NULL,NULL,&ctx->dmrepart)); */
383       nz = 1;
384       bz = DM_BOUNDARY_NONE;
385       break;
386     case 3:
387       PetscCall(PetscInfo(pc, "PCTelescope: setting up the DMDA on comm subset (3D)\n"));
388       /* PetscCall(DMDACreate3d(subcomm,bx,by,bz,stencil,nx,ny,nz,
389          PETSC_DECIDE,PETSC_DECIDE,PETSC_DECIDE, ndof,nsw, NULL,NULL,NULL,&ctx->dmrepart)); */
390       break;
391     }
392     /*
393      The API DMDACreate1d(), DMDACreate2d(), DMDACreate3d() does not allow us to set/append
394      a unique option prefix for the DM, thus I prefer to expose the contents of these API's here.
395      This allows users to control the partitioning of the subDM.
396     */
397     PetscCall(DMDACreate(subcomm, &ctx->dmrepart));
398     /* Set unique option prefix name */
399     PetscCall(KSPGetOptionsPrefix(sred->ksp, &prefix));
400     PetscCall(DMSetOptionsPrefix(ctx->dmrepart, prefix));
401     PetscCall(DMAppendOptionsPrefix(ctx->dmrepart, "repart_"));
402     /* standard setup from DMDACreate{1,2,3}d() */
403     PetscCall(DMSetDimension(ctx->dmrepart, dim));
404     PetscCall(DMDASetSizes(ctx->dmrepart, nx, ny, nz));
405     PetscCall(DMDASetNumProcs(ctx->dmrepart, PETSC_DECIDE, PETSC_DECIDE, PETSC_DECIDE));
406     PetscCall(DMDASetBoundaryType(ctx->dmrepart, bx, by, bz));
407     PetscCall(DMDASetDof(ctx->dmrepart, ndof));
408     PetscCall(DMDASetStencilType(ctx->dmrepart, stencil));
409     PetscCall(DMDASetStencilWidth(ctx->dmrepart, nsw));
410     PetscCall(DMDASetOwnershipRanges(ctx->dmrepart, NULL, NULL, NULL));
411     PetscCall(DMSetFromOptions(ctx->dmrepart));
412     PetscCall(DMSetUp(ctx->dmrepart));
413     /* Set refinement factors and interpolation type from the partent */
414     PetscCall(DMDASetRefinementFactor(ctx->dmrepart, refine_x, refine_y, refine_z));
415     PetscCall(DMDASetInterpolationType(ctx->dmrepart, itype));
416 
417     PetscCall(DMDAGetInfo(ctx->dmrepart, NULL, NULL, NULL, NULL, &ctx->Mp_re, &ctx->Np_re, &ctx->Pp_re, NULL, NULL, NULL, NULL, NULL, NULL));
418     PetscCall(DMDAGetOwnershipRanges(ctx->dmrepart, &_range_i_re, &_range_j_re, &_range_k_re));
419 
420     ctx->dmrepart->ops->creatematrix              = dm->ops->creatematrix;
421     ctx->dmrepart->ops->createdomaindecomposition = dm->ops->createdomaindecomposition;
422   }
423 
424   /* generate ranges for repartitioned dm */
425   /* note - assume rank 0 always participates */
426   /* TODO: use a single MPI call */
427   PetscCallMPI(MPI_Bcast(&ctx->Mp_re, 1, MPIU_INT, 0, comm));
428   PetscCallMPI(MPI_Bcast(&ctx->Np_re, 1, MPIU_INT, 0, comm));
429   PetscCallMPI(MPI_Bcast(&ctx->Pp_re, 1, MPIU_INT, 0, comm));
430 
431   PetscCall(PetscCalloc3(ctx->Mp_re, &ctx->range_i_re, ctx->Np_re, &ctx->range_j_re, ctx->Pp_re, &ctx->range_k_re));
432 
433   if (_range_i_re) PetscCall(PetscArraycpy(ctx->range_i_re, _range_i_re, ctx->Mp_re));
434   if (_range_j_re) PetscCall(PetscArraycpy(ctx->range_j_re, _range_j_re, ctx->Np_re));
435   if (_range_k_re) PetscCall(PetscArraycpy(ctx->range_k_re, _range_k_re, ctx->Pp_re));
436 
437   /* TODO: use a single MPI call */
438   PetscCallMPI(MPI_Bcast(ctx->range_i_re, ctx->Mp_re, MPIU_INT, 0, comm));
439   PetscCallMPI(MPI_Bcast(ctx->range_j_re, ctx->Np_re, MPIU_INT, 0, comm));
440   PetscCallMPI(MPI_Bcast(ctx->range_k_re, ctx->Pp_re, MPIU_INT, 0, comm));
441 
442   PetscCall(PetscMalloc3(ctx->Mp_re, &ctx->start_i_re, ctx->Np_re, &ctx->start_j_re, ctx->Pp_re, &ctx->start_k_re));
443 
444   sum = 0;
445   for (k = 0; k < ctx->Mp_re; k++) {
446     ctx->start_i_re[k] = sum;
447     sum += ctx->range_i_re[k];
448   }
449 
450   sum = 0;
451   for (k = 0; k < ctx->Np_re; k++) {
452     ctx->start_j_re[k] = sum;
453     sum += ctx->range_j_re[k];
454   }
455 
456   sum = 0;
457   for (k = 0; k < ctx->Pp_re; k++) {
458     ctx->start_k_re[k] = sum;
459     sum += ctx->range_k_re[k];
460   }
461 
462   /* attach repartitioned dm to child ksp */
463   {
464     PetscErrorCode (*dmksp_func)(KSP, Mat, Mat, void *);
465     void *dmksp_ctx;
466 
467     PetscCall(DMKSPGetComputeOperators(dm, &dmksp_func, &dmksp_ctx));
468 
469     /* attach dm to ksp on sub communicator */
470     if (PCTelescope_isActiveRank(sred)) {
471       PetscCall(KSPSetDM(sred->ksp, ctx->dmrepart));
472 
473       if (!dmksp_func || sred->ignore_kspcomputeoperators) {
474         PetscCall(KSPSetDMActive(sred->ksp, PETSC_FALSE));
475       } else {
476         /* sub ksp inherits dmksp_func and context provided by user */
477         PetscCall(KSPSetComputeOperators(sred->ksp, dmksp_func, dmksp_ctx));
478         PetscCall(KSPSetDMActive(sred->ksp, PETSC_TRUE));
479       }
480     }
481   }
482   PetscFunctionReturn(PETSC_SUCCESS);
483 }
484 
485 static PetscErrorCode PCTelescopeSetUp_dmda_permutation_3d(PC pc, PC_Telescope sred, PC_Telescope_DMDACtx *ctx)
486 {
487   DM       dm;
488   MPI_Comm comm;
489   Mat      Pscalar, P;
490   PetscInt ndof;
491   PetscInt i, j, k, location, startI[3], endI[3], lenI[3], nx, ny, nz;
492   PetscInt sr, er, Mr;
493   Vec      V;
494 
495   PetscFunctionBegin;
496   PetscCall(PetscInfo(pc, "PCTelescope: setting up the permutation matrix (DMDA-3D)\n"));
497   PetscCall(PetscObjectGetComm((PetscObject)pc, &comm));
498 
499   PetscCall(PCGetDM(pc, &dm));
500   PetscCall(DMDAGetInfo(dm, NULL, &nx, &ny, &nz, NULL, NULL, NULL, &ndof, NULL, NULL, NULL, NULL, NULL));
501 
502   PetscCall(DMGetGlobalVector(dm, &V));
503   PetscCall(VecGetSize(V, &Mr));
504   PetscCall(VecGetOwnershipRange(V, &sr, &er));
505   PetscCall(DMRestoreGlobalVector(dm, &V));
506   sr = sr / ndof;
507   er = er / ndof;
508   Mr = Mr / ndof;
509 
510   PetscCall(MatCreate(comm, &Pscalar));
511   PetscCall(MatSetSizes(Pscalar, (er - sr), (er - sr), Mr, Mr));
512   PetscCall(MatSetType(Pscalar, MATAIJ));
513   PetscCall(MatSeqAIJSetPreallocation(Pscalar, 1, NULL));
514   PetscCall(MatMPIAIJSetPreallocation(Pscalar, 1, NULL, 1, NULL));
515 
516   PetscCall(DMDAGetCorners(dm, NULL, NULL, NULL, &lenI[0], &lenI[1], &lenI[2]));
517   PetscCall(DMDAGetCorners(dm, &startI[0], &startI[1], &startI[2], &endI[0], &endI[1], &endI[2]));
518   endI[0] += startI[0];
519   endI[1] += startI[1];
520   endI[2] += startI[2];
521 
522   for (k = startI[2]; k < endI[2]; k++) {
523     for (j = startI[1]; j < endI[1]; j++) {
524       for (i = startI[0]; i < endI[0]; i++) {
525         PetscMPIInt rank_ijk_re, rank_reI[3];
526         PetscInt    s0_re;
527         PetscInt    ii, jj, kk, local_ijk_re, mapped_ijk;
528         PetscInt    lenI_re[3];
529 
530         location = (i - startI[0]) + (j - startI[1]) * lenI[0] + (k - startI[2]) * lenI[0] * lenI[1];
531         PetscCall(_DMDADetermineRankFromGlobalIJK(3, i, j, k, ctx->Mp_re, ctx->Np_re, ctx->Pp_re, ctx->start_i_re, ctx->start_j_re, ctx->start_k_re, ctx->range_i_re, ctx->range_j_re, ctx->range_k_re, &rank_reI[0], &rank_reI[1], &rank_reI[2], &rank_ijk_re));
532         PetscCall(_DMDADetermineGlobalS0(3, rank_ijk_re, ctx->Mp_re, ctx->Np_re, ctx->Pp_re, ctx->range_i_re, ctx->range_j_re, ctx->range_k_re, &s0_re));
533         ii = i - ctx->start_i_re[rank_reI[0]];
534         PetscCheck(ii >= 0, PETSC_COMM_SELF, PETSC_ERR_USER, "[dmdarepart-perm3d] index error ii");
535         jj = j - ctx->start_j_re[rank_reI[1]];
536         PetscCheck(jj >= 0, PETSC_COMM_SELF, PETSC_ERR_USER, "[dmdarepart-perm3d] index error jj");
537         kk = k - ctx->start_k_re[rank_reI[2]];
538         PetscCheck(kk >= 0, PETSC_COMM_SELF, PETSC_ERR_USER, "[dmdarepart-perm3d] index error kk");
539         lenI_re[0]   = ctx->range_i_re[rank_reI[0]];
540         lenI_re[1]   = ctx->range_j_re[rank_reI[1]];
541         lenI_re[2]   = ctx->range_k_re[rank_reI[2]];
542         local_ijk_re = ii + jj * lenI_re[0] + kk * lenI_re[0] * lenI_re[1];
543         mapped_ijk   = s0_re + local_ijk_re;
544         PetscCall(MatSetValue(Pscalar, sr + location, mapped_ijk, 1.0, INSERT_VALUES));
545       }
546     }
547   }
548   PetscCall(MatAssemblyBegin(Pscalar, MAT_FINAL_ASSEMBLY));
549   PetscCall(MatAssemblyEnd(Pscalar, MAT_FINAL_ASSEMBLY));
550   PetscCall(MatCreateMAIJ(Pscalar, ndof, &P));
551   PetscCall(MatDestroy(&Pscalar));
552   ctx->permutation = P;
553   PetscFunctionReturn(PETSC_SUCCESS);
554 }
555 
556 static PetscErrorCode PCTelescopeSetUp_dmda_permutation_2d(PC pc, PC_Telescope sred, PC_Telescope_DMDACtx *ctx)
557 {
558   DM       dm;
559   MPI_Comm comm;
560   Mat      Pscalar, P;
561   PetscInt ndof;
562   PetscInt i, j, location, startI[2], endI[2], lenI[2], nx, ny, nz;
563   PetscInt sr, er, Mr;
564   Vec      V;
565 
566   PetscFunctionBegin;
567   PetscCall(PetscInfo(pc, "PCTelescope: setting up the permutation matrix (DMDA-2D)\n"));
568   PetscCall(PetscObjectGetComm((PetscObject)pc, &comm));
569   PetscCall(PCGetDM(pc, &dm));
570   PetscCall(DMDAGetInfo(dm, NULL, &nx, &ny, &nz, NULL, NULL, NULL, &ndof, NULL, NULL, NULL, NULL, NULL));
571   PetscCall(DMGetGlobalVector(dm, &V));
572   PetscCall(VecGetSize(V, &Mr));
573   PetscCall(VecGetOwnershipRange(V, &sr, &er));
574   PetscCall(DMRestoreGlobalVector(dm, &V));
575   sr = sr / ndof;
576   er = er / ndof;
577   Mr = Mr / ndof;
578 
579   PetscCall(MatCreate(comm, &Pscalar));
580   PetscCall(MatSetSizes(Pscalar, (er - sr), (er - sr), Mr, Mr));
581   PetscCall(MatSetType(Pscalar, MATAIJ));
582   PetscCall(MatSeqAIJSetPreallocation(Pscalar, 1, NULL));
583   PetscCall(MatMPIAIJSetPreallocation(Pscalar, 1, NULL, 1, NULL));
584 
585   PetscCall(DMDAGetCorners(dm, NULL, NULL, NULL, &lenI[0], &lenI[1], NULL));
586   PetscCall(DMDAGetCorners(dm, &startI[0], &startI[1], NULL, &endI[0], &endI[1], NULL));
587   endI[0] += startI[0];
588   endI[1] += startI[1];
589 
590   for (j = startI[1]; j < endI[1]; j++) {
591     for (i = startI[0]; i < endI[0]; i++) {
592       PetscMPIInt rank_ijk_re, rank_reI[3];
593       PetscInt    s0_re;
594       PetscInt    ii, jj, local_ijk_re, mapped_ijk;
595       PetscInt    lenI_re[3];
596 
597       location = (i - startI[0]) + (j - startI[1]) * lenI[0];
598       PetscCall(_DMDADetermineRankFromGlobalIJK(2, i, j, 0, ctx->Mp_re, ctx->Np_re, ctx->Pp_re, ctx->start_i_re, ctx->start_j_re, ctx->start_k_re, ctx->range_i_re, ctx->range_j_re, ctx->range_k_re, &rank_reI[0], &rank_reI[1], NULL, &rank_ijk_re));
599 
600       PetscCall(_DMDADetermineGlobalS0(2, rank_ijk_re, ctx->Mp_re, ctx->Np_re, ctx->Pp_re, ctx->range_i_re, ctx->range_j_re, ctx->range_k_re, &s0_re));
601 
602       ii = i - ctx->start_i_re[rank_reI[0]];
603       PetscCheck(ii >= 0, PETSC_COMM_SELF, PETSC_ERR_USER, "[dmdarepart-perm2d] index error ii");
604       jj = j - ctx->start_j_re[rank_reI[1]];
605       PetscCheck(jj >= 0, PETSC_COMM_SELF, PETSC_ERR_USER, "[dmdarepart-perm2d] index error jj");
606 
607       lenI_re[0]   = ctx->range_i_re[rank_reI[0]];
608       lenI_re[1]   = ctx->range_j_re[rank_reI[1]];
609       local_ijk_re = ii + jj * lenI_re[0];
610       mapped_ijk   = s0_re + local_ijk_re;
611       PetscCall(MatSetValue(Pscalar, sr + location, mapped_ijk, 1.0, INSERT_VALUES));
612     }
613   }
614   PetscCall(MatAssemblyBegin(Pscalar, MAT_FINAL_ASSEMBLY));
615   PetscCall(MatAssemblyEnd(Pscalar, MAT_FINAL_ASSEMBLY));
616   PetscCall(MatCreateMAIJ(Pscalar, ndof, &P));
617   PetscCall(MatDestroy(&Pscalar));
618   ctx->permutation = P;
619   PetscFunctionReturn(PETSC_SUCCESS);
620 }
621 
622 static PetscErrorCode PCTelescopeSetUp_dmda_scatters(PC pc, PC_Telescope sred, PC_Telescope_DMDACtx *ctx)
623 {
624   Vec        xred, yred, xtmp, x, xp;
625   VecScatter scatter;
626   IS         isin;
627   Mat        B;
628   PetscInt   m, bs, st, ed;
629   MPI_Comm   comm;
630 
631   PetscFunctionBegin;
632   PetscCall(PetscObjectGetComm((PetscObject)pc, &comm));
633   PetscCall(PCGetOperators(pc, NULL, &B));
634   PetscCall(MatCreateVecs(B, &x, NULL));
635   PetscCall(MatGetBlockSize(B, &bs));
636   PetscCall(VecDuplicate(x, &xp));
637   m    = 0;
638   xred = NULL;
639   yred = NULL;
640   if (PCTelescope_isActiveRank(sred)) {
641     PetscCall(DMCreateGlobalVector(ctx->dmrepart, &xred));
642     PetscCall(VecDuplicate(xred, &yred));
643     PetscCall(VecGetOwnershipRange(xred, &st, &ed));
644     PetscCall(ISCreateStride(comm, ed - st, st, 1, &isin));
645     PetscCall(VecGetLocalSize(xred, &m));
646   } else {
647     PetscCall(VecGetOwnershipRange(x, &st, &ed));
648     PetscCall(ISCreateStride(comm, 0, st, 1, &isin));
649   }
650   PetscCall(ISSetBlockSize(isin, bs));
651   PetscCall(VecCreate(comm, &xtmp));
652   PetscCall(VecSetSizes(xtmp, m, PETSC_DECIDE));
653   PetscCall(VecSetBlockSize(xtmp, bs));
654   PetscCall(VecSetType(xtmp, ((PetscObject)x)->type_name));
655   PetscCall(VecScatterCreate(x, isin, xtmp, NULL, &scatter));
656   sred->xred    = xred;
657   sred->yred    = yred;
658   sred->isin    = isin;
659   sred->scatter = scatter;
660   sred->xtmp    = xtmp;
661 
662   ctx->xp = xp;
663   PetscCall(VecDestroy(&x));
664   PetscFunctionReturn(PETSC_SUCCESS);
665 }
666 
667 PetscErrorCode PCTelescopeSetUp_dmda(PC pc, PC_Telescope sred)
668 {
669   PC_Telescope_DMDACtx *ctx;
670   PetscInt              dim;
671   DM                    dm;
672   MPI_Comm              comm;
673 
674   PetscFunctionBegin;
675   PetscCall(PetscInfo(pc, "PCTelescope: setup (DMDA)\n"));
676   PetscCall(PetscNew(&ctx));
677   sred->dm_ctx = (void *)ctx;
678 
679   PetscCall(PetscObjectGetComm((PetscObject)pc, &comm));
680   PetscCall(PCGetDM(pc, &dm));
681   PetscCall(DMDAGetInfo(dm, &dim, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL));
682 
683   PetscCall(PCTelescopeSetUp_dmda_repart(pc, sred, ctx));
684   PetscCall(PCTelescopeSetUp_dmda_repart_coors(pc, sred, ctx));
685   switch (dim) {
686   case 1:
687     SETERRQ(comm, PETSC_ERR_SUP, "Telescope: DMDA (1D) repartitioning not provided");
688   case 2:
689     PetscCall(PCTelescopeSetUp_dmda_permutation_2d(pc, sred, ctx));
690     break;
691   case 3:
692     PetscCall(PCTelescopeSetUp_dmda_permutation_3d(pc, sred, ctx));
693     break;
694   }
695   PetscCall(PCTelescopeSetUp_dmda_scatters(pc, sred, ctx));
696   PetscFunctionReturn(PETSC_SUCCESS);
697 }
698 
699 static PetscErrorCode PCTelescopeMatCreate_dmda_dmactivefalse(PC pc, PC_Telescope sred, MatReuse reuse, Mat *A)
700 {
701   PC_Telescope_DMDACtx *ctx;
702   MPI_Comm              comm, subcomm;
703   Mat                   Bperm, Bred, B, P;
704   PetscInt              nr, nc;
705   IS                    isrow, iscol;
706   Mat                   Blocal, *_Blocal;
707 
708   PetscFunctionBegin;
709   PetscCall(PetscInfo(pc, "PCTelescope: updating the redundant preconditioned operator (DMDA)\n"));
710   PetscCall(PetscObjectGetComm((PetscObject)pc, &comm));
711   subcomm = PetscSubcommChild(sred->psubcomm);
712   ctx     = (PC_Telescope_DMDACtx *)sred->dm_ctx;
713 
714   PetscCall(PCGetOperators(pc, NULL, &B));
715   PetscCall(MatGetSize(B, &nr, &nc));
716 
717   P = ctx->permutation;
718   PetscCall(MatPtAP(B, P, MAT_INITIAL_MATRIX, 1.1, &Bperm));
719 
720   /* Get submatrices */
721   isrow = sred->isin;
722   PetscCall(ISCreateStride(comm, nc, 0, 1, &iscol));
723 
724   PetscCall(MatCreateSubMatrices(Bperm, 1, &isrow, &iscol, MAT_INITIAL_MATRIX, &_Blocal));
725   Blocal = *_Blocal;
726   Bred   = NULL;
727   if (PCTelescope_isActiveRank(sred)) {
728     PetscInt mm;
729 
730     if (reuse != MAT_INITIAL_MATRIX) Bred = *A;
731     PetscCall(MatGetSize(Blocal, &mm, NULL));
732     /* PetscCall(MatCreateMPIMatConcatenateSeqMat(subcomm,Blocal,PETSC_DECIDE,reuse,&Bred)); */
733     PetscCall(MatCreateMPIMatConcatenateSeqMat(subcomm, Blocal, mm, reuse, &Bred));
734   }
735   *A = Bred;
736 
737   PetscCall(ISDestroy(&iscol));
738   PetscCall(MatDestroy(&Bperm));
739   PetscCall(MatDestroyMatrices(1, &_Blocal));
740   PetscFunctionReturn(PETSC_SUCCESS);
741 }
742 
743 PetscErrorCode PCTelescopeMatCreate_dmda(PC pc, PC_Telescope sred, MatReuse reuse, Mat *A)
744 {
745   DM dm;
746   PetscErrorCode (*dmksp_func)(KSP, Mat, Mat, void *);
747   void *dmksp_ctx;
748 
749   PetscFunctionBegin;
750   PetscCall(PCGetDM(pc, &dm));
751   PetscCall(DMKSPGetComputeOperators(dm, &dmksp_func, &dmksp_ctx));
752   /* We assume that dmksp_func = NULL, is equivalent to dmActive = PETSC_FALSE */
753   if (dmksp_func && !sred->ignore_kspcomputeoperators) {
754     DM  dmrepart;
755     Mat Ak;
756 
757     *A = NULL;
758     if (PCTelescope_isActiveRank(sred)) {
759       PetscCall(KSPGetDM(sred->ksp, &dmrepart));
760       if (reuse == MAT_INITIAL_MATRIX) {
761         PetscCall(DMCreateMatrix(dmrepart, &Ak));
762         *A = Ak;
763       } else if (reuse == MAT_REUSE_MATRIX) {
764         Ak = *A;
765       }
766       /*
767        There is no need to explicitly assemble the operator now,
768        the sub-KSP will call the method provided to KSPSetComputeOperators() during KSPSetUp()
769       */
770     }
771   } else {
772     PetscCall(PCTelescopeMatCreate_dmda_dmactivefalse(pc, sred, reuse, A));
773   }
774   PetscFunctionReturn(PETSC_SUCCESS);
775 }
776 
777 static PetscErrorCode PCTelescopeSubNullSpaceCreate_dmda_Telescope(PC pc, PC_Telescope sred, MatNullSpace nullspace, MatNullSpace *sub_nullspace)
778 {
779   PetscBool             has_const;
780   PetscInt              i, k, n = 0;
781   const Vec            *vecs;
782   Vec                  *sub_vecs = NULL;
783   MPI_Comm              subcomm;
784   PC_Telescope_DMDACtx *ctx;
785 
786   PetscFunctionBegin;
787   ctx     = (PC_Telescope_DMDACtx *)sred->dm_ctx;
788   subcomm = PetscSubcommChild(sred->psubcomm);
789   PetscCall(MatNullSpaceGetVecs(nullspace, &has_const, &n, &vecs));
790 
791   if (PCTelescope_isActiveRank(sred)) {
792     /* create new vectors */
793     if (n) PetscCall(VecDuplicateVecs(sred->xred, n, &sub_vecs));
794   }
795 
796   /* copy entries */
797   for (k = 0; k < n; k++) {
798     const PetscScalar *x_array;
799     PetscScalar       *LA_sub_vec;
800     PetscInt           st, ed;
801 
802     /* permute vector into ordering associated with re-partitioned dmda */
803     PetscCall(MatMultTranspose(ctx->permutation, vecs[k], ctx->xp));
804 
805     /* pull in vector x->xtmp */
806     PetscCall(VecScatterBegin(sred->scatter, ctx->xp, sred->xtmp, INSERT_VALUES, SCATTER_FORWARD));
807     PetscCall(VecScatterEnd(sred->scatter, ctx->xp, sred->xtmp, INSERT_VALUES, SCATTER_FORWARD));
808 
809     /* copy vector entries into xred */
810     PetscCall(VecGetArrayRead(sred->xtmp, &x_array));
811     if (sub_vecs) {
812       if (sub_vecs[k]) {
813         PetscCall(VecGetOwnershipRange(sub_vecs[k], &st, &ed));
814         PetscCall(VecGetArray(sub_vecs[k], &LA_sub_vec));
815         for (i = 0; i < ed - st; i++) LA_sub_vec[i] = x_array[i];
816         PetscCall(VecRestoreArray(sub_vecs[k], &LA_sub_vec));
817       }
818     }
819     PetscCall(VecRestoreArrayRead(sred->xtmp, &x_array));
820   }
821 
822   if (PCTelescope_isActiveRank(sred)) {
823     /* create new (near) nullspace for redundant object */
824     PetscCall(MatNullSpaceCreate(subcomm, has_const, n, sub_vecs, sub_nullspace));
825     PetscCall(VecDestroyVecs(n, &sub_vecs));
826     PetscCheck(!nullspace->remove, PetscObjectComm((PetscObject)pc), PETSC_ERR_SUP, "Propagation of custom remove callbacks not supported when propagating (near) nullspaces with PCTelescope");
827     PetscCheck(!nullspace->rmctx, PetscObjectComm((PetscObject)pc), PETSC_ERR_SUP, "Propagation of custom remove callback context not supported when propagating (near) nullspaces with PCTelescope");
828   }
829   PetscFunctionReturn(PETSC_SUCCESS);
830 }
831 
832 PetscErrorCode PCTelescopeMatNullSpaceCreate_dmda(PC pc, PC_Telescope sred, Mat sub_mat)
833 {
834   Mat B;
835 
836   PetscFunctionBegin;
837   PetscCall(PCGetOperators(pc, NULL, &B));
838   {
839     MatNullSpace nullspace, sub_nullspace;
840     PetscCall(MatGetNullSpace(B, &nullspace));
841     if (nullspace) {
842       PetscCall(PetscInfo(pc, "PCTelescope: generating nullspace (DMDA)\n"));
843       PetscCall(PCTelescopeSubNullSpaceCreate_dmda_Telescope(pc, sred, nullspace, &sub_nullspace));
844       if (PCTelescope_isActiveRank(sred)) {
845         PetscCall(MatSetNullSpace(sub_mat, sub_nullspace));
846         PetscCall(MatNullSpaceDestroy(&sub_nullspace));
847       }
848     }
849   }
850   {
851     MatNullSpace nearnullspace, sub_nearnullspace;
852     PetscCall(MatGetNearNullSpace(B, &nearnullspace));
853     if (nearnullspace) {
854       PetscCall(PetscInfo(pc, "PCTelescope: generating near nullspace (DMDA)\n"));
855       PetscCall(PCTelescopeSubNullSpaceCreate_dmda_Telescope(pc, sred, nearnullspace, &sub_nearnullspace));
856       if (PCTelescope_isActiveRank(sred)) {
857         PetscCall(MatSetNearNullSpace(sub_mat, sub_nearnullspace));
858         PetscCall(MatNullSpaceDestroy(&sub_nearnullspace));
859       }
860     }
861   }
862   PetscFunctionReturn(PETSC_SUCCESS);
863 }
864 
865 PetscErrorCode PCApply_Telescope_dmda(PC pc, Vec x, Vec y)
866 {
867   PC_Telescope          sred = (PC_Telescope)pc->data;
868   Mat                   perm;
869   Vec                   xtmp, xp, xred, yred;
870   PetscInt              i, st, ed;
871   VecScatter            scatter;
872   PetscScalar          *array;
873   const PetscScalar    *x_array;
874   PC_Telescope_DMDACtx *ctx;
875 
876   ctx     = (PC_Telescope_DMDACtx *)sred->dm_ctx;
877   xtmp    = sred->xtmp;
878   scatter = sred->scatter;
879   xred    = sred->xred;
880   yred    = sred->yred;
881   perm    = ctx->permutation;
882   xp      = ctx->xp;
883 
884   PetscFunctionBegin;
885   PetscCall(PetscCitationsRegister(citation, &cited));
886 
887   /* permute vector into ordering associated with re-partitioned dmda */
888   PetscCall(MatMultTranspose(perm, x, xp));
889 
890   /* pull in vector x->xtmp */
891   PetscCall(VecScatterBegin(scatter, xp, xtmp, INSERT_VALUES, SCATTER_FORWARD));
892   PetscCall(VecScatterEnd(scatter, xp, xtmp, INSERT_VALUES, SCATTER_FORWARD));
893 
894   /* copy vector entries into xred */
895   PetscCall(VecGetArrayRead(xtmp, &x_array));
896   if (xred) {
897     PetscScalar *LA_xred;
898     PetscCall(VecGetOwnershipRange(xred, &st, &ed));
899 
900     PetscCall(VecGetArray(xred, &LA_xred));
901     for (i = 0; i < ed - st; i++) LA_xred[i] = x_array[i];
902     PetscCall(VecRestoreArray(xred, &LA_xred));
903   }
904   PetscCall(VecRestoreArrayRead(xtmp, &x_array));
905 
906   /* solve */
907   if (PCTelescope_isActiveRank(sred)) {
908     PetscCall(KSPSolve(sred->ksp, xred, yred));
909     PetscCall(KSPCheckSolve(sred->ksp, pc, yred));
910   }
911 
912   /* return vector */
913   PetscCall(VecGetArray(xtmp, &array));
914   if (yred) {
915     const PetscScalar *LA_yred;
916     PetscCall(VecGetOwnershipRange(yred, &st, &ed));
917     PetscCall(VecGetArrayRead(yred, &LA_yred));
918     for (i = 0; i < ed - st; i++) array[i] = LA_yred[i];
919     PetscCall(VecRestoreArrayRead(yred, &LA_yred));
920   }
921   PetscCall(VecRestoreArray(xtmp, &array));
922   PetscCall(VecScatterBegin(scatter, xtmp, xp, INSERT_VALUES, SCATTER_REVERSE));
923   PetscCall(VecScatterEnd(scatter, xtmp, xp, INSERT_VALUES, SCATTER_REVERSE));
924   PetscCall(MatMult(perm, xp, y));
925   PetscFunctionReturn(PETSC_SUCCESS);
926 }
927 
928 PetscErrorCode PCApplyRichardson_Telescope_dmda(PC pc, Vec x, Vec y, Vec w, PetscReal rtol, PetscReal abstol, PetscReal dtol, PetscInt its, PetscBool zeroguess, PetscInt *outits, PCRichardsonConvergedReason *reason)
929 {
930   PC_Telescope          sred = (PC_Telescope)pc->data;
931   Mat                   perm;
932   Vec                   xtmp, xp, yred;
933   PetscInt              i, st, ed;
934   VecScatter            scatter;
935   const PetscScalar    *x_array;
936   PetscBool             default_init_guess_value = PETSC_FALSE;
937   PC_Telescope_DMDACtx *ctx;
938 
939   PetscFunctionBegin;
940   ctx     = (PC_Telescope_DMDACtx *)sred->dm_ctx;
941   xtmp    = sred->xtmp;
942   scatter = sred->scatter;
943   yred    = sred->yred;
944   perm    = ctx->permutation;
945   xp      = ctx->xp;
946 
947   PetscCheck(its <= 1, PetscObjectComm((PetscObject)pc), PETSC_ERR_SUP, "PCApplyRichardson_Telescope_dmda only supports max_it = 1");
948   *reason = (PCRichardsonConvergedReason)0;
949 
950   if (!zeroguess) {
951     PetscCall(PetscInfo(pc, "PCTelescopeDMDA: Scattering y for non-zero-initial guess\n"));
952     /* permute vector into ordering associated with re-partitioned dmda */
953     PetscCall(MatMultTranspose(perm, y, xp));
954 
955     /* pull in vector x->xtmp */
956     PetscCall(VecScatterBegin(scatter, xp, xtmp, INSERT_VALUES, SCATTER_FORWARD));
957     PetscCall(VecScatterEnd(scatter, xp, xtmp, INSERT_VALUES, SCATTER_FORWARD));
958 
959     /* copy vector entries into xred */
960     PetscCall(VecGetArrayRead(xtmp, &x_array));
961     if (yred) {
962       PetscScalar *LA_yred;
963       PetscCall(VecGetOwnershipRange(yred, &st, &ed));
964       PetscCall(VecGetArray(yred, &LA_yred));
965       for (i = 0; i < ed - st; i++) LA_yred[i] = x_array[i];
966       PetscCall(VecRestoreArray(yred, &LA_yred));
967     }
968     PetscCall(VecRestoreArrayRead(xtmp, &x_array));
969   }
970 
971   if (PCTelescope_isActiveRank(sred)) {
972     PetscCall(KSPGetInitialGuessNonzero(sred->ksp, &default_init_guess_value));
973     if (!zeroguess) PetscCall(KSPSetInitialGuessNonzero(sred->ksp, PETSC_TRUE));
974   }
975 
976   PetscCall(PCApply_Telescope_dmda(pc, x, y));
977 
978   if (PCTelescope_isActiveRank(sred)) PetscCall(KSPSetInitialGuessNonzero(sred->ksp, default_init_guess_value));
979 
980   if (!*reason) *reason = PCRICHARDSON_CONVERGED_ITS;
981   *outits = 1;
982   PetscFunctionReturn(PETSC_SUCCESS);
983 }
984 
985 PetscErrorCode PCReset_Telescope_dmda(PC pc)
986 {
987   PC_Telescope          sred = (PC_Telescope)pc->data;
988   PC_Telescope_DMDACtx *ctx;
989 
990   PetscFunctionBegin;
991   ctx = (PC_Telescope_DMDACtx *)sred->dm_ctx;
992   PetscCall(VecDestroy(&ctx->xp));
993   PetscCall(MatDestroy(&ctx->permutation));
994   PetscCall(DMDestroy(&ctx->dmrepart));
995   PetscCall(PetscFree3(ctx->range_i_re, ctx->range_j_re, ctx->range_k_re));
996   PetscCall(PetscFree3(ctx->start_i_re, ctx->start_j_re, ctx->start_k_re));
997   PetscFunctionReturn(PETSC_SUCCESS);
998 }
999 
1000 static PetscErrorCode DMView_DA_Short_3d(DM dm, PetscViewer v)
1001 {
1002   PetscInt    M, N, P, m, n, p, ndof, nsw;
1003   MPI_Comm    comm;
1004   PetscMPIInt size;
1005   const char *prefix;
1006 
1007   PetscFunctionBegin;
1008   PetscCall(PetscObjectGetComm((PetscObject)dm, &comm));
1009   PetscCallMPI(MPI_Comm_size(comm, &size));
1010   PetscCall(DMGetOptionsPrefix(dm, &prefix));
1011   PetscCall(DMDAGetInfo(dm, NULL, &M, &N, &P, &m, &n, &p, &ndof, &nsw, NULL, NULL, NULL, NULL));
1012   if (prefix) PetscCall(PetscViewerASCIIPrintf(v, "DMDA Object:    (%s)    %d MPI processes\n", prefix, size));
1013   else PetscCall(PetscViewerASCIIPrintf(v, "DMDA Object:    %d MPI processes\n", size));
1014   PetscCall(PetscViewerASCIIPrintf(v, "  M %" PetscInt_FMT " N %" PetscInt_FMT " P %" PetscInt_FMT " m %" PetscInt_FMT " n %" PetscInt_FMT " p %" PetscInt_FMT " dof %" PetscInt_FMT " overlap %" PetscInt_FMT "\n", M, N, P, m, n, p, ndof, nsw));
1015   PetscFunctionReturn(PETSC_SUCCESS);
1016 }
1017 
1018 static PetscErrorCode DMView_DA_Short_2d(DM dm, PetscViewer v)
1019 {
1020   PetscInt    M, N, m, n, ndof, nsw;
1021   MPI_Comm    comm;
1022   PetscMPIInt size;
1023   const char *prefix;
1024 
1025   PetscFunctionBegin;
1026   PetscCall(PetscObjectGetComm((PetscObject)dm, &comm));
1027   PetscCallMPI(MPI_Comm_size(comm, &size));
1028   PetscCall(DMGetOptionsPrefix(dm, &prefix));
1029   PetscCall(DMDAGetInfo(dm, NULL, &M, &N, NULL, &m, &n, NULL, &ndof, &nsw, NULL, NULL, NULL, NULL));
1030   if (prefix) PetscCall(PetscViewerASCIIPrintf(v, "DMDA Object:    (%s)    %d MPI processes\n", prefix, size));
1031   else PetscCall(PetscViewerASCIIPrintf(v, "DMDA Object:    %d MPI processes\n", size));
1032   PetscCall(PetscViewerASCIIPrintf(v, "  M %" PetscInt_FMT " N %" PetscInt_FMT " m %" PetscInt_FMT " n %" PetscInt_FMT " dof %" PetscInt_FMT " overlap %" PetscInt_FMT "\n", M, N, m, n, ndof, nsw));
1033   PetscFunctionReturn(PETSC_SUCCESS);
1034 }
1035 
1036 PetscErrorCode DMView_DA_Short(DM dm, PetscViewer v)
1037 {
1038   PetscInt dim;
1039 
1040   PetscFunctionBegin;
1041   PetscCall(DMDAGetInfo(dm, &dim, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL));
1042   switch (dim) {
1043   case 2:
1044     PetscCall(DMView_DA_Short_2d(dm, v));
1045     break;
1046   case 3:
1047     PetscCall(DMView_DA_Short_3d(dm, v));
1048     break;
1049   }
1050   PetscFunctionReturn(PETSC_SUCCESS);
1051 }
1052