Actual source code: fgmres.c
1: /*
2: This file implements FGMRES (a Generalized Minimal Residual) method.
3: Reference: Saad, 1993.
5: Preconditioning: If the preconditioner is constant then this fgmres
6: code is equivalent to RIGHT-PRECONDITIONED GMRES.
7: FGMRES is a modification of gmres that allows the preconditioner to change
8: at each iteration.
10: Restarts: Restarts are basically solves with x0 not equal to zero.
11: */
13: #include <../src/ksp/ksp/impls/gmres/fgmres/fgmresimpl.h>
14: #define FGMRES_DELTA_DIRECTIONS 10
15: #define FGMRES_DEFAULT_MAXK 30
16: static PetscErrorCode KSPFGMRESGetNewVectors(KSP, PetscInt);
17: static PetscErrorCode KSPFGMRESUpdateHessenberg(KSP, PetscInt, PetscBool, PetscReal *);
18: static PetscErrorCode KSPFGMRESBuildSoln(PetscScalar *, Vec, Vec, KSP, PetscInt);
20: static PetscErrorCode KSPSetUp_FGMRES(KSP ksp)
21: {
22: PetscInt max_k;
23: KSP_FGMRES *fgmres = (KSP_FGMRES *)ksp->data;
25: PetscFunctionBegin;
26: max_k = fgmres->max_k;
28: PetscCall(KSPSetUp_GMRES(ksp));
30: PetscCall(PetscMalloc1(max_k + 2, &fgmres->prevecs));
31: PetscCall(PetscMalloc1(max_k + 2, &fgmres->prevecs_user_work));
33: /* fgmres->vv_allocated includes extra work vectors, which are not used in the additional
34: block of vectors used to store the preconditioned directions, hence the -VEC_OFFSET
35: term for this first allocation of vectors holding preconditioned directions */
36: PetscCall(KSPCreateVecs(ksp, fgmres->vv_allocated - VEC_OFFSET, &fgmres->prevecs_user_work[0], 0, NULL));
37: for (PetscInt k = 0; k < fgmres->vv_allocated - VEC_OFFSET; k++) fgmres->prevecs[k] = fgmres->prevecs_user_work[0][k];
38: PetscFunctionReturn(PETSC_SUCCESS);
39: }
41: static PetscErrorCode KSPFGMRESResidual(KSP ksp)
42: {
43: KSP_FGMRES *fgmres = (KSP_FGMRES *)ksp->data;
44: Mat Amat, Pmat;
46: PetscFunctionBegin;
47: PetscCall(PCGetOperators(ksp->pc, &Amat, &Pmat));
49: /* put A*x into VEC_TEMP */
50: PetscCall(KSP_MatMult(ksp, Amat, ksp->vec_sol, VEC_TEMP));
51: /* now put residual (-A*x + f) into vec_vv(0) */
52: PetscCall(VecWAXPY(VEC_VV(0), -1.0, VEC_TEMP, ksp->vec_rhs));
53: PetscFunctionReturn(PETSC_SUCCESS);
54: }
56: static PetscErrorCode KSPFGMRESCycle(PetscInt *itcount, KSP ksp)
57: {
58: KSP_FGMRES *fgmres = (KSP_FGMRES *)ksp->data;
59: PetscReal res_norm;
60: PetscReal hapbnd, tt;
61: PetscBool hapend = PETSC_FALSE; /* indicates happy breakdown ending */
62: PetscInt loc_it; /* local count of # of dir. in Krylov space */
63: PetscInt max_k = fgmres->max_k; /* max # of directions Krylov space */
64: Mat Amat, Pmat;
66: PetscFunctionBegin;
67: /* Number of pseudo iterations since last restart is the number
68: of prestart directions */
69: loc_it = 0;
71: /* note: (fgmres->it) is always set one less than (loc_it) It is used in
72: KSPBUILDSolution_FGMRES, where it is passed to KSPFGMRESBuildSoln.
73: Note that when KSPFGMRESBuildSoln is called from this function,
74: (loc_it -1) is passed, so the two are equivalent */
75: fgmres->it = (loc_it - 1);
77: /* initial residual is in VEC_VV(0) - compute its norm*/
78: PetscCall(VecNorm(VEC_VV(0), NORM_2, &res_norm));
79: KSPCheckNorm(ksp, res_norm);
81: /* The first entry in the right-hand side of the Hessenberg system is just
82: the initial residual norm */
83: *RS(0) = res_norm;
85: ksp->rnorm = res_norm;
86: PetscCall(KSPLogResidualHistory(ksp, res_norm));
87: PetscCall(KSPMonitor(ksp, ksp->its, res_norm));
89: /* check for the convergence - maybe the current guess is good enough */
90: PetscCall((*ksp->converged)(ksp, ksp->its, res_norm, &ksp->reason, ksp->cnvP));
91: if (ksp->reason) {
92: if (itcount) *itcount = 0;
93: PetscFunctionReturn(PETSC_SUCCESS);
94: }
96: /* scale VEC_VV (the initial residual) */
97: PetscCall(VecScale(VEC_VV(0), 1.0 / res_norm));
99: /* MAIN ITERATION LOOP BEGINNING*/
100: /* keep iterating until we have converged OR generated the max number
101: of directions OR reached the max number of iterations for the method */
102: while (!ksp->reason && loc_it < max_k && ksp->its < ksp->max_it) {
103: if (loc_it) {
104: PetscCall(KSPLogResidualHistory(ksp, res_norm));
105: PetscCall(KSPMonitor(ksp, ksp->its, res_norm));
106: }
107: fgmres->it = (loc_it - 1);
109: /* see if more space is needed for work vectors */
110: if (fgmres->vv_allocated <= loc_it + VEC_OFFSET + 1) {
111: PetscCall(KSPFGMRESGetNewVectors(ksp, loc_it + 1));
112: /* (loc_it+1) is passed in as number of the first vector that should
113: be allocated */
114: }
116: /* CHANGE THE PRECONDITIONER? */
117: /* ModifyPC is the callback function that can be used to
118: change the PC or its attributes before its applied */
119: PetscCall((*fgmres->modifypc)(ksp, ksp->its, loc_it, res_norm, fgmres->modifyctx));
121: /* apply PRECONDITIONER to direction vector and store with
122: preconditioned vectors in prevec */
123: PetscCall(KSP_PCApply(ksp, VEC_VV(loc_it), PREVEC(loc_it)));
125: PetscCall(PCGetOperators(ksp->pc, &Amat, &Pmat));
126: /* Multiply preconditioned vector by operator - put in VEC_VV(loc_it+1) */
127: PetscCall(KSP_MatMult(ksp, Amat, PREVEC(loc_it), VEC_VV(1 + loc_it)));
129: /* update Hessenberg matrix and do Gram-Schmidt - new direction is in
130: VEC_VV(1+loc_it)*/
131: PetscCall((*ksp->orthog)(ksp, &VEC_VV(0), loc_it + 1, NULL, HH(0, loc_it)));
132: PetscCall(PetscArraycpy(HES(0, loc_it), HH(0, loc_it), loc_it + 1));
134: /* new entry in Hessenberg is the 2-norm of our new direction */
135: PetscCall(VecNorm(VEC_VV(loc_it + 1), NORM_2, &tt));
136: KSPCheckNorm(ksp, tt);
138: *HH(loc_it + 1, loc_it) = tt;
139: *HES(loc_it + 1, loc_it) = tt;
141: /* Happy Breakdown Check */
142: hapbnd = PetscAbsScalar((tt) / *RS(loc_it));
143: /* RS(loc_it) contains the res_norm from the last iteration */
144: hapbnd = PetscMin(fgmres->haptol, hapbnd);
145: if (tt > hapbnd) {
146: /* scale new direction by its norm */
147: PetscCall(VecScale(VEC_VV(loc_it + 1), 1.0 / tt));
148: } else {
149: /* This happens when the solution is exactly reached. */
150: /* So there is no new direction... */
151: PetscCall(VecSet(VEC_TEMP, 0.0)); /* set VEC_TEMP to 0 */
152: hapend = PETSC_TRUE;
153: }
154: /* note that for FGMRES we could get HES(loc_it+1, loc_it) = 0 and the
155: current solution would not be exact if HES was singular. Note that
156: HH non-singular implies that HES is no singular, and HES is guaranteed
157: to be nonsingular when PREVECS are linearly independent and A is
158: nonsingular (in GMRES, the nonsingularity of A implies the nonsingularity
159: of HES). So we should really add a check to verify that HES is nonsingular.*/
161: /* Now apply rotations to the new column of Hessenberg (and the right-hand side of the system),
162: calculate new rotation, and get new residual norm at the same time*/
163: PetscCall(KSPFGMRESUpdateHessenberg(ksp, loc_it, hapend, &res_norm));
164: if (ksp->reason) break;
166: loc_it++;
167: fgmres->it = (loc_it - 1); /* Add this here in case it has converged */
169: PetscCall(PetscObjectSAWsTakeAccess((PetscObject)ksp));
170: ksp->its++;
171: ksp->rnorm = res_norm;
172: PetscCall(PetscObjectSAWsGrantAccess((PetscObject)ksp));
174: PetscCall((*ksp->converged)(ksp, ksp->its, res_norm, &ksp->reason, ksp->cnvP));
176: /* Catch error in happy breakdown and signal convergence and break from loop */
177: if (hapend) {
178: if (!ksp->reason) {
179: PetscCheck(!ksp->errorifnotconverged, PetscObjectComm((PetscObject)ksp), PETSC_ERR_NOT_CONVERGED, "Reached happy break down, but convergence was not indicated. Residual norm = %g", (double)res_norm);
180: ksp->reason = KSP_DIVERGED_BREAKDOWN;
181: break;
182: }
183: }
184: }
185: /* END OF ITERATION LOOP */
187: if (itcount) *itcount = loc_it;
189: /*
190: Down here we have to solve for the "best" coefficients of the Krylov
191: columns, add the solution values together, and possibly unwind the
192: preconditioning from the solution
193: */
195: /* Form the solution (or the solution so far) */
196: /* Note: must pass in (loc_it-1) for iteration count so that KSPFGMRESBuildSoln
197: properly navigates */
199: PetscCall(KSPFGMRESBuildSoln(RS(0), ksp->vec_sol, ksp->vec_sol, ksp, loc_it - 1));
201: /* Monitor if we know that we will not return for a restart */
202: if (ksp->reason == KSP_CONVERGED_ITERATING && ksp->its >= ksp->max_it) ksp->reason = KSP_DIVERGED_ITS;
203: if (loc_it && ksp->reason) {
204: PetscCall(KSPMonitor(ksp, ksp->its, res_norm));
205: PetscCall(KSPLogResidualHistory(ksp, res_norm));
206: }
207: PetscFunctionReturn(PETSC_SUCCESS);
208: }
210: static PetscErrorCode KSPSolve_FGMRES(KSP ksp)
211: {
212: PetscInt cycle_its = 0; /* iterations done in a call to KSPFGMRESCycle */
213: KSP_FGMRES *fgmres = (KSP_FGMRES *)ksp->data;
215: PetscFunctionBegin;
216: PetscCall(PetscObjectSAWsTakeAccess((PetscObject)ksp));
217: ksp->its = 0;
218: PetscCall(PetscObjectSAWsGrantAccess((PetscObject)ksp));
220: /* Compute the initial (NOT preconditioned) residual */
221: if (!ksp->guess_zero) {
222: PetscCall(KSPFGMRESResidual(ksp));
223: } else { /* guess is 0 so residual is F (which is in ksp->vec_rhs) */
224: PetscCall(VecCopy(ksp->vec_rhs, VEC_VV(0)));
225: }
226: /* This may be true only on a subset of MPI ranks; setting it here so it will be detected by the first norm computation in the Krylov method */
227: PetscCall(VecFlag(VEC_VV(0), ksp->reason == KSP_DIVERGED_PC_FAILED));
229: /* now the residual is in VEC_VV(0) - which is what
230: KSPFGMRESCycle expects... */
232: PetscCall(KSPFGMRESCycle(&cycle_its, ksp));
233: while (!ksp->reason) {
234: PetscCall(KSPFGMRESResidual(ksp));
235: if (ksp->its >= ksp->max_it) break;
236: PetscCall(KSPFGMRESCycle(&cycle_its, ksp));
237: }
238: /* mark lack of convergence */
239: if (ksp->its >= ksp->max_it && !ksp->reason) ksp->reason = KSP_DIVERGED_ITS;
240: PetscFunctionReturn(PETSC_SUCCESS);
241: }
243: extern PetscErrorCode KSPReset_FGMRES(KSP);
245: static PetscErrorCode KSPDestroy_FGMRES(KSP ksp)
246: {
247: PetscFunctionBegin;
248: PetscCall(KSPReset_FGMRES(ksp));
249: PetscCall(PetscObjectComposeFunction((PetscObject)ksp, "KSPFlexibleSetModifyPC_C", NULL));
250: PetscCall(KSPDestroy_GMRES(ksp));
251: PetscFunctionReturn(PETSC_SUCCESS);
252: }
254: static PetscErrorCode KSPFGMRESBuildSoln(PetscScalar *nrs, Vec vguess, Vec vdest, KSP ksp, PetscInt it)
255: {
256: PetscScalar tt;
257: PetscInt ii, k, j;
258: KSP_FGMRES *fgmres = (KSP_FGMRES *)ksp->data;
260: PetscFunctionBegin;
261: /* Solve for solution vector that minimizes the residual */
263: /* If it is < 0, no fgmres steps have been performed */
264: if (it < 0) {
265: PetscCall(VecCopy(vguess, vdest)); /* VecCopy() is smart, exists immediately if vguess == vdest */
266: PetscFunctionReturn(PETSC_SUCCESS);
267: }
269: /* so fgmres steps HAVE been performed */
271: /* solve the upper triangular system - RS is the right side and HH is
272: the upper triangular matrix - put soln in nrs */
273: if (*HH(it, it) != 0.0) {
274: nrs[it] = *RS(it) / *HH(it, it);
275: } else {
276: nrs[it] = 0.0;
277: }
278: for (ii = 1; ii <= it; ii++) {
279: k = it - ii;
280: tt = *RS(k);
281: for (j = k + 1; j <= it; j++) tt = tt - *HH(k, j) * nrs[j];
282: nrs[k] = tt / *HH(k, k);
283: }
285: /* Accumulate the correction to the soln of the preconditioned prob. in
286: VEC_TEMP - note that we use the preconditioned vectors */
287: PetscCall(VecMAXPBY(VEC_TEMP, it + 1, nrs, 0, &PREVEC(0)));
289: /* put updated solution into vdest.*/
290: if (vdest != vguess) {
291: PetscCall(VecCopy(VEC_TEMP, vdest));
292: PetscCall(VecAXPY(vdest, 1.0, vguess));
293: } else { /* replace guess with solution */
294: PetscCall(VecAXPY(vdest, 1.0, VEC_TEMP));
295: }
296: PetscFunctionReturn(PETSC_SUCCESS);
297: }
299: static PetscErrorCode KSPFGMRESUpdateHessenberg(KSP ksp, PetscInt it, PetscBool hapend, PetscReal *res)
300: {
301: PetscScalar *hh, *cc, *ss, tt;
302: KSP_FGMRES *fgmres = (KSP_FGMRES *)ksp->data;
304: PetscFunctionBegin;
305: hh = HH(0, it); /* pointer to beginning of column to update - so
306: incrementing hh "steps down" the (it+1)th col of HH*/
307: cc = CC(0); /* beginning of cosine rotations */
308: ss = SS(0); /* beginning of sine rotations */
310: /* Apply all the previously computed plane rotations to the new column
311: of the Hessenberg matrix */
312: /* Note: this uses the rotation [conj(c) s ; -s c], c= cos(theta), s= sin(theta),
313: and some refs have [c s ; -conj(s) c] (don't be confused!) */
315: for (PetscInt j = 1; j <= it; j++) {
316: tt = *hh;
317: *hh = PetscConj(*cc) * tt + *ss * *(hh + 1);
318: hh++;
319: *hh = *cc++ * *hh - (*ss++ * tt);
320: /* hh, cc, and ss have all been incremented one by end of loop */
321: }
323: /*
324: compute the new plane rotation, and apply it to:
325: 1) the right-hand side of the Hessenberg system (RS)
326: note: it affects RS(it) and RS(it+1)
327: 2) the new column of the Hessenberg matrix
328: note: it affects HH(it,it) which is currently pointed to
329: by hh and HH(it+1, it) (*(hh+1))
330: thus obtaining the updated value of the residual...
331: */
333: /* compute new plane rotation */
335: if (!hapend) {
336: tt = PetscSqrtScalar(PetscConj(*hh) * *hh + PetscConj(*(hh + 1)) * *(hh + 1));
337: if (tt == 0.0) {
338: ksp->reason = KSP_DIVERGED_NULL;
339: PetscFunctionReturn(PETSC_SUCCESS);
340: }
342: *cc = *hh / tt; /* new cosine value */
343: *ss = *(hh + 1) / tt; /* new sine value */
345: /* apply to 1) and 2) */
346: *RS(it + 1) = -(*ss * *RS(it));
347: *RS(it) = PetscConj(*cc) * *RS(it);
348: *hh = PetscConj(*cc) * *hh + *ss * *(hh + 1);
350: /* residual is the last element (it+1) of right-hand side! */
351: *res = PetscAbsScalar(*RS(it + 1));
353: } else { /* happy breakdown: HH(it+1, it) = 0, therefore we don't need to apply
354: another rotation matrix (so RH doesn't change). The new residual is
355: always the new sine term times the residual from last time (RS(it)),
356: but now the new sine rotation would be zero...so the residual should
357: be zero...so we will multiply "zero" by the last residual. This might
358: not be exactly what we want to do here -could just return "zero". */
360: *res = 0.0;
361: }
362: PetscFunctionReturn(PETSC_SUCCESS);
363: }
365: static PetscErrorCode KSPFGMRESGetNewVectors(KSP ksp, PetscInt it)
366: {
367: KSP_FGMRES *fgmres = (KSP_FGMRES *)ksp->data;
368: PetscInt nwork = fgmres->nwork_alloc; /* number of work vector chunks allocated */
369: PetscInt nalloc; /* number to allocate */
371: PetscFunctionBegin;
372: nalloc = fgmres->delta_allocate; /* number of vectors to allocate
373: in a single chunk */
375: /* Adjust the number to allocate to make sure that we don't exceed the
376: number of available slots (fgmres->vecs_allocated)*/
377: if (it + VEC_OFFSET + nalloc >= fgmres->vecs_allocated) nalloc = fgmres->vecs_allocated - it - VEC_OFFSET;
378: if (!nalloc) PetscFunctionReturn(PETSC_SUCCESS);
380: fgmres->vv_allocated += nalloc; /* vv_allocated is the number of vectors allocated */
382: /* work vectors */
383: PetscCall(KSPCreateVecs(ksp, nalloc, &fgmres->user_work[nwork], 0, NULL));
384: for (PetscInt k = 0; k < nalloc; k++) fgmres->vecs[it + VEC_OFFSET + k] = fgmres->user_work[nwork][k];
385: /* specify size of chunk allocated */
386: fgmres->mwork_alloc[nwork] = nalloc;
388: /* preconditioned vectors */
389: PetscCall(KSPCreateVecs(ksp, nalloc, &fgmres->prevecs_user_work[nwork], 0, NULL));
390: for (PetscInt k = 0; k < nalloc; k++) fgmres->prevecs[it + k] = fgmres->prevecs_user_work[nwork][k];
392: /* increment the number of work vector chunks */
393: fgmres->nwork_alloc++;
394: PetscFunctionReturn(PETSC_SUCCESS);
395: }
397: static PetscErrorCode KSPBuildSolution_FGMRES(KSP ksp, Vec ptr, Vec *result)
398: {
399: KSP_FGMRES *fgmres = (KSP_FGMRES *)ksp->data;
401: PetscFunctionBegin;
402: if (!ptr) {
403: if (!fgmres->sol_temp) PetscCall(VecDuplicate(ksp->vec_sol, &fgmres->sol_temp));
404: ptr = fgmres->sol_temp;
405: }
406: if (!fgmres->nrs) {
407: /* allocate the work area */
408: PetscCall(PetscMalloc1(fgmres->max_k, &fgmres->nrs));
409: }
411: PetscCall(KSPFGMRESBuildSoln(fgmres->nrs, ksp->vec_sol, ptr, ksp, fgmres->it));
412: if (result) *result = ptr;
413: PetscFunctionReturn(PETSC_SUCCESS);
414: }
416: static PetscErrorCode KSPSetFromOptions_FGMRES(KSP ksp, PetscOptionItems PetscOptionsObject)
417: {
418: PetscBool flg;
420: PetscFunctionBegin;
421: PetscCall(KSPSetFromOptions_GMRES(ksp, PetscOptionsObject));
422: PetscOptionsHeadBegin(PetscOptionsObject, "KSP flexible GMRES Options");
423: PetscCall(PetscOptionsBoolGroupBegin("-ksp_fgmres_modifypcnochange", "do not vary the preconditioner", "KSPFlexibleSetModifyPC", &flg));
424: if (flg) PetscCall(KSPFlexibleSetModifyPC(ksp, KSPFlexibleModifyPCNoChange, NULL, NULL));
425: PetscCall(PetscOptionsBoolGroupEnd("-ksp_fgmres_modifypcksp", "vary the KSP based preconditioner", "KSPFlexibleSetModifyPC", &flg));
426: if (flg) PetscCall(KSPFlexibleSetModifyPC(ksp, KSPFlexibleModifyPCKSP, NULL, NULL));
427: PetscOptionsHeadEnd();
428: PetscFunctionReturn(PETSC_SUCCESS);
429: }
431: static PetscErrorCode KSPFlexibleSetModifyPC_FGMRES(KSP ksp, KSPFlexibleModifyPCFn *fcn, PetscCtx ctx, PetscCtxDestroyFn *d)
432: {
433: PetscFunctionBegin;
435: ((KSP_FGMRES *)ksp->data)->modifypc = fcn;
436: ((KSP_FGMRES *)ksp->data)->modifydestroy = d;
437: ((KSP_FGMRES *)ksp->data)->modifyctx = ctx;
438: PetscFunctionReturn(PETSC_SUCCESS);
439: }
441: PetscErrorCode KSPReset_FGMRES(KSP ksp)
442: {
443: KSP_FGMRES *fgmres = (KSP_FGMRES *)ksp->data;
444: PetscInt i;
446: PetscFunctionBegin;
447: PetscCall(PetscFree(fgmres->prevecs));
448: if (fgmres->nwork_alloc > 0) {
449: i = 0;
450: /* In the first allocation we allocated VEC_OFFSET fewer vectors in prevecs */
451: PetscCall(VecDestroyVecs(fgmres->mwork_alloc[i] - VEC_OFFSET, &fgmres->prevecs_user_work[i]));
452: for (i = 1; i < fgmres->nwork_alloc; i++) PetscCall(VecDestroyVecs(fgmres->mwork_alloc[i], &fgmres->prevecs_user_work[i]));
453: }
454: PetscCall(PetscFree(fgmres->prevecs_user_work));
455: if (fgmres->modifydestroy) PetscCall((*fgmres->modifydestroy)(&fgmres->modifyctx));
456: PetscCall(KSPReset_GMRES(ksp));
457: PetscFunctionReturn(PETSC_SUCCESS);
458: }
460: static PetscErrorCode KSPGMRESSetRestart_FGMRES(KSP ksp, PetscInt max_k)
461: {
462: KSP_FGMRES *gmres = (KSP_FGMRES *)ksp->data;
464: PetscFunctionBegin;
465: PetscCheck(max_k >= 1, PetscObjectComm((PetscObject)ksp), PETSC_ERR_ARG_OUTOFRANGE, "Restart must be positive");
466: if (!ksp->setupstage) {
467: gmres->max_k = max_k;
468: } else if (gmres->max_k != max_k) {
469: gmres->max_k = max_k;
470: ksp->setupstage = KSP_SETUP_NEW;
471: /* free the data structures, then create them again */
472: PetscCall(KSPReset_FGMRES(ksp));
473: }
474: PetscFunctionReturn(PETSC_SUCCESS);
475: }
477: static PetscErrorCode KSPGMRESGetRestart_FGMRES(KSP ksp, PetscInt *max_k)
478: {
479: KSP_FGMRES *gmres = (KSP_FGMRES *)ksp->data;
481: PetscFunctionBegin;
482: *max_k = gmres->max_k;
483: PetscFunctionReturn(PETSC_SUCCESS);
484: }
486: /*MC
487: KSPFGMRES - Implements the Flexible Generalized Minimal Residual method, flexible GMRES. [](sec_flexibleksp)
489: Options Database Keys:
490: + -ksp_gmres_restart restart - the number of Krylov directions to orthogonalize against
491: . -ksp_gmres_haptol tol - sets the tolerance for "happy breakdown" (exact convergence)
492: . -ksp_gmres_preallocate - preallocate all the Krylov search directions initially (otherwise groups of vectors are allocated as needed)
493: . -ksp_gmres_krylov_monitor - plot the Krylov space generated
494: . -ksp_fgmres_modifypcnochange - do not change the preconditioner between iterations
495: - -ksp_fgmres_modifypcksp - modify the preconditioner using `KSPFlexibleModifyPCKSP()`
497: Level: beginner
499: Notes:
500: See `KSPFlexibleSetModifyPC()` for how to vary the preconditioner between iterations
502: GMRES requires that the preconditioner used is a linear operator. Flexible GMRES allows the preconditioner to be a nonlinear operator. This
503: allows, for example, Flexible GMRES to use GMRES solvers or other Krylov solvers (which are nonlinear operators in general) inside the preconditioner
504: used by `KSPFGMRES`. For example, the options `-ksp_type fgmres -pc_type ksp -ksp_ksp_type bcgs -ksp_view -ksp_pc_type jacobi` make the preconditioner
505: (or inner solver) be bi-CG-stab with a preconditioner of `PCJACOBI`. `KSPFCG` provides a flexible version of the preconditioned conjugate gradient method.
507: Only right preconditioning is supported.
509: The following options `-ksp_type fgmres -pc_type ksp -ksp_ksp_type bcgs -ksp_view -ksp_pc_type jacobi` make the preconditioner (or inner solver)
510: be bi-CG-stab with a preconditioner of `PCJACOBI`
512: Developer Note:
513: This object is subclassed off of `KSPGMRES`, see the source code in src/ksp/ksp/impls/gmres for comments on the structure of the code
515: Contributed by:
516: Allison Baker
518: .seealso: [](ch_ksp), [](sec_flexibleksp), `KSPCreate()`, `KSPSetType()`, `KSPType`, `KSP`, `KSPGMRES`, `KSPLGMRES`, `KSPFCG`,
519: `KSPGMRESSetRestart()`, `KSPGMRESSetHapTol()`, `KSPGMRESSetPreAllocateVectors()`, `KSPOrthogonalizationSet()`, `KSPOrthogonalizationGet()`,
520: `KSPOrthogonalizationClassicalGramSchmidt()`, `KSPOrthogonalizationModifiedGramSchmidt()`,
521: `KSPOrthogonalizationCGSRefinementType`, `KSPOrthogonalizationSetCGSRefinementType()`, `KSPOrthogonalizationGetCGSRefinementType()`, `KSPGMRESMonitorKrylov()`, `KSPFlexibleSetModifyPC()`,
522: `KSPFlexibleModifyPCKSP()`
523: M*/
525: PETSC_EXTERN PetscErrorCode KSPCreate_FGMRES(KSP ksp)
526: {
527: KSP_FGMRES *fgmres;
529: PetscFunctionBegin;
530: PetscCall(PetscNew(&fgmres));
532: ksp->data = (void *)fgmres;
533: ksp->ops->buildsolution = KSPBuildSolution_FGMRES;
534: ksp->ops->setup = KSPSetUp_FGMRES;
535: ksp->ops->solve = KSPSolve_FGMRES;
536: ksp->ops->reset = KSPReset_FGMRES;
537: ksp->ops->destroy = KSPDestroy_FGMRES;
538: ksp->ops->view = KSPView_GMRES;
539: ksp->ops->setfromoptions = KSPSetFromOptions_FGMRES;
540: ksp->ops->computeextremesingularvalues = KSPComputeExtremeSingularValues_GMRES;
541: ksp->ops->computeeigenvalues = KSPComputeEigenvalues_GMRES;
543: PetscCall(KSPSetSupportedNorm(ksp, KSP_NORM_UNPRECONDITIONED, PC_RIGHT, 3));
544: PetscCall(KSPSetSupportedNorm(ksp, KSP_NORM_NONE, PC_RIGHT, 1));
546: PetscCall(PetscObjectComposeFunction((PetscObject)ksp, "KSPGMRESSetPreAllocateVectors_C", KSPGMRESSetPreAllocateVectors_GMRES));
547: PetscCall(PetscObjectComposeFunction((PetscObject)ksp, "KSPGMRESSetRestart_C", KSPGMRESSetRestart_FGMRES));
548: PetscCall(PetscObjectComposeFunction((PetscObject)ksp, "KSPGMRESGetRestart_C", KSPGMRESGetRestart_FGMRES));
549: PetscCall(PetscObjectComposeFunction((PetscObject)ksp, "KSPFlexibleSetModifyPC_C", KSPFlexibleSetModifyPC_FGMRES));
551: fgmres->haptol = 1.0e-30;
552: fgmres->q_preallocate = PETSC_FALSE;
553: fgmres->delta_allocate = FGMRES_DELTA_DIRECTIONS;
554: fgmres->nrs = NULL;
555: fgmres->sol_temp = NULL;
556: fgmres->max_k = FGMRES_DEFAULT_MAXK;
557: fgmres->Rsvd = NULL;
558: fgmres->modifypc = KSPFlexibleModifyPCNoChange;
559: fgmres->modifyctx = NULL;
560: fgmres->modifydestroy = NULL;
561: PetscFunctionReturn(PETSC_SUCCESS);
562: }