Actual source code: fgmres.c


  2: /*
  3:     This file implements FGMRES (a Generalized Minimal Residual) method.
  4:     Reference:  Saad, 1993.

  6:     Preconditioning:  If the preconditioner is constant then this fgmres
  7:     code is equivalent to RIGHT-PRECONDITIONED GMRES.
  8:     FGMRES is a modification of gmres that allows the preconditioner to change
  9:     at each iteration.

 11:     Restarts:  Restarts are basically solves with x0 not equal to zero.

 13:        Contributed by Allison Baker

 15: */

 17: #include <../src/ksp/ksp/impls/gmres/fgmres/fgmresimpl.h>
 18: #define FGMRES_DELTA_DIRECTIONS 10
 19: #define FGMRES_DEFAULT_MAXK     30
 20: static PetscErrorCode KSPFGMRESGetNewVectors(KSP,PetscInt);
 21: static PetscErrorCode KSPFGMRESUpdateHessenberg(KSP,PetscInt,PetscBool,PetscReal*);
 22: static PetscErrorCode KSPFGMRESBuildSoln(PetscScalar*,Vec,Vec,KSP,PetscInt);

 24: /*

 26:     KSPSetUp_FGMRES - Sets up the workspace needed by fgmres.

 28:     This is called once, usually automatically by KSPSolve() or KSPSetUp(),
 29:     but can be called directly by KSPSetUp().

 31: */
 32: PetscErrorCode    KSPSetUp_FGMRES(KSP ksp)
 33: {
 35:   PetscInt       max_k,k;
 36:   KSP_FGMRES     *fgmres = (KSP_FGMRES*)ksp->data;

 39:   max_k = fgmres->max_k;

 41:   KSPSetUp_GMRES(ksp);

 43:   PetscMalloc1(max_k+2,&fgmres->prevecs);
 44:   PetscMalloc1(max_k+2,&fgmres->prevecs_user_work);
 45:   PetscLogObjectMemory((PetscObject)ksp,(max_k+2)*(2*sizeof(void*)));

 47:   /* fgmres->vv_allocated includes extra work vectors, which are not used in the additional
 48:      block of vectors used to store the preconditioned directions, hence  the -VEC_OFFSET
 49:      term for this first allocation of vectors holding preconditioned directions */
 50:   KSPCreateVecs(ksp,fgmres->vv_allocated-VEC_OFFSET,&fgmres->prevecs_user_work[0],0,NULL);
 51:   PetscLogObjectParents(ksp,fgmres->vv_allocated-VEC_OFFSET,fgmres->prevecs_user_work[0]);
 52:   for (k=0; k < fgmres->vv_allocated - VEC_OFFSET ; k++) {
 53:     fgmres->prevecs[k] = fgmres->prevecs_user_work[0][k];
 54:   }
 55:   return(0);
 56: }

 58: /*
 59:     KSPFGMRESResidual - This routine computes the initial residual (NOT PRECONDITIONED)
 60: */
 61: static PetscErrorCode KSPFGMRESResidual(KSP ksp)
 62: {
 63:   KSP_FGMRES     *fgmres = (KSP_FGMRES*)(ksp->data);
 64:   Mat            Amat,Pmat;

 68:   PCGetOperators(ksp->pc,&Amat,&Pmat);

 70:   /* put A*x into VEC_TEMP */
 71:   KSP_MatMult(ksp,Amat,ksp->vec_sol,VEC_TEMP);
 72:   /* now put residual (-A*x + f) into vec_vv(0) */
 73:   VecWAXPY(VEC_VV(0),-1.0,VEC_TEMP,ksp->vec_rhs);
 74:   return(0);
 75: }

 77: /*

 79:     KSPFGMRESCycle - Run fgmres, possibly with restart.  Return residual
 80:                   history if requested.

 82:     input parameters:
 83: .        fgmres  - structure containing parameters and work areas

 85:     output parameters:
 86: .        itcount - number of iterations used.  If null, ignored.
 87: .        converged - 0 if not converged

 89:     Notes:
 90:     On entry, the value in vector VEC_VV(0) should be
 91:     the initial residual.

 93:  */
 94: PetscErrorCode KSPFGMRESCycle(PetscInt *itcount,KSP ksp)
 95: {

 97:   KSP_FGMRES     *fgmres = (KSP_FGMRES*)(ksp->data);
 98:   PetscReal      res_norm;
 99:   PetscReal      hapbnd,tt;
100:   PetscBool      hapend = PETSC_FALSE;  /* indicates happy breakdown ending */
102:   PetscInt       loc_it;                /* local count of # of dir. in Krylov space */
103:   PetscInt       max_k = fgmres->max_k; /* max # of directions Krylov space */
104:   Mat            Amat,Pmat;

107:   /* Number of pseudo iterations since last restart is the number
108:      of prestart directions */
109:   loc_it = 0;

111:   /* note: (fgmres->it) is always set one less than (loc_it) It is used in
112:      KSPBUILDSolution_FGMRES, where it is passed to KSPFGMRESBuildSoln.
113:      Note that when KSPFGMRESBuildSoln is called from this function,
114:      (loc_it -1) is passed, so the two are equivalent */
115:   fgmres->it = (loc_it - 1);

117:   /* initial residual is in VEC_VV(0)  - compute its norm*/
118:   VecNorm(VEC_VV(0),NORM_2,&res_norm);
119:   KSPCheckNorm(ksp,res_norm);

121:   /* first entry in right-hand-side of hessenberg system is just
122:      the initial residual norm */
123:   *RS(0) = res_norm;

125:   ksp->rnorm = res_norm;
126:   KSPLogResidualHistory(ksp,res_norm);
127:   KSPMonitor(ksp,ksp->its,res_norm);

129:   /* check for the convergence - maybe the current guess is good enough */
130:   (*ksp->converged)(ksp,ksp->its,res_norm,&ksp->reason,ksp->cnvP);
131:   if (ksp->reason) {
132:     if (itcount) *itcount = 0;
133:     return(0);
134:   }

136:   /* scale VEC_VV (the initial residual) */
137:   VecScale(VEC_VV(0),1.0/res_norm);

139:   /* MAIN ITERATION LOOP BEGINNING*/
140:   /* keep iterating until we have converged OR generated the max number
141:      of directions OR reached the max number of iterations for the method */
142:   while (!ksp->reason && loc_it < max_k && ksp->its < ksp->max_it) {
143:     if (loc_it) {
144:       KSPLogResidualHistory(ksp,res_norm);
145:       KSPMonitor(ksp,ksp->its,res_norm);
146:     }
147:     fgmres->it = (loc_it - 1);

149:     /* see if more space is needed for work vectors */
150:     if (fgmres->vv_allocated <= loc_it + VEC_OFFSET + 1) {
151:       KSPFGMRESGetNewVectors(ksp,loc_it+1);
152:       /* (loc_it+1) is passed in as number of the first vector that should
153:          be allocated */
154:     }

156:     /* CHANGE THE PRECONDITIONER? */
157:     /* ModifyPC is the callback function that can be used to
158:        change the PC or its attributes before its applied */
159:     (*fgmres->modifypc)(ksp,ksp->its,loc_it,res_norm,fgmres->modifyctx);

161:     /* apply PRECONDITIONER to direction vector and store with
162:        preconditioned vectors in prevec */
163:     KSP_PCApply(ksp,VEC_VV(loc_it),PREVEC(loc_it));

165:     PCGetOperators(ksp->pc,&Amat,&Pmat);
166:     /* Multiply preconditioned vector by operator - put in VEC_VV(loc_it+1) */
167:     KSP_MatMult(ksp,Amat,PREVEC(loc_it),VEC_VV(1+loc_it));

169:     /* update hessenberg matrix and do Gram-Schmidt - new direction is in
170:        VEC_VV(1+loc_it)*/
171:     (*fgmres->orthog)(ksp,loc_it);

173:     /* new entry in hessenburg is the 2-norm of our new direction */
174:     VecNorm(VEC_VV(loc_it+1),NORM_2,&tt);

176:     *HH(loc_it+1,loc_it)  = tt;
177:     *HES(loc_it+1,loc_it) = tt;

179:     /* Happy Breakdown Check */
180:     hapbnd = PetscAbsScalar((tt) / *RS(loc_it));
181:     /* RS(loc_it) contains the res_norm from the last iteration  */
182:     hapbnd = PetscMin(fgmres->haptol,hapbnd);
183:     if (tt > hapbnd) {
184:       /* scale new direction by its norm */
185:       VecScale(VEC_VV(loc_it+1),1.0/tt);
186:     } else {
187:       /* This happens when the solution is exactly reached. */
188:       /* So there is no new direction... */
189:       VecSet(VEC_TEMP,0.0);     /* set VEC_TEMP to 0 */
190:       hapend = PETSC_TRUE;
191:     }
192:     /* note that for FGMRES we could get HES(loc_it+1, loc_it)  = 0 and the
193:        current solution would not be exact if HES was singular.  Note that
194:        HH non-singular implies that HES is no singular, and HES is guaranteed
195:        to be nonsingular when PREVECS are linearly independent and A is
196:        nonsingular (in GMRES, the nonsingularity of A implies the nonsingularity
197:        of HES). So we should really add a check to verify that HES is nonsingular.*/

199:     /* Now apply rotations to new col of hessenberg (and right side of system),
200:        calculate new rotation, and get new residual norm at the same time*/
201:     KSPFGMRESUpdateHessenberg(ksp,loc_it,hapend,&res_norm);
202:     if (ksp->reason) break;

204:     loc_it++;
205:     fgmres->it = (loc_it-1);   /* Add this here in case it has converged */

207:     PetscObjectSAWsTakeAccess((PetscObject)ksp);
208:     ksp->its++;
209:     ksp->rnorm = res_norm;
210:     PetscObjectSAWsGrantAccess((PetscObject)ksp);

212:     (*ksp->converged)(ksp,ksp->its,res_norm,&ksp->reason,ksp->cnvP);

214:     /* Catch error in happy breakdown and signal convergence and break from loop */
215:     if (hapend) {
216:       if (!ksp->reason) {
217:         if (ksp->errorifnotconverged) SETERRQ1(PetscObjectComm((PetscObject)ksp),PETSC_ERR_NOT_CONVERGED,"You reached the happy break down, but convergence was not indicated. Residual norm = %g",(double)res_norm);
218:         else {
219:           ksp->reason = KSP_DIVERGED_BREAKDOWN;
220:           break;
221:         }
222:       }
223:     }
224:   }
225:   /* END OF ITERATION LOOP */
226:   KSPLogResidualHistory(ksp,res_norm);

228:   /*
229:      Monitor if we know that we will not return for a restart */
230:   if (loc_it && (ksp->reason || ksp->its >= ksp->max_it)) {
231:     KSPMonitor(ksp,ksp->its,res_norm);
232:   }

234:   if (itcount) *itcount = loc_it;

236:   /*
237:     Down here we have to solve for the "best" coefficients of the Krylov
238:     columns, add the solution values together, and possibly unwind the
239:     preconditioning from the solution
240:    */

242:   /* Form the solution (or the solution so far) */
243:   /* Note: must pass in (loc_it-1) for iteration count so that KSPFGMRESBuildSoln
244:      properly navigates */

246:   KSPFGMRESBuildSoln(RS(0),ksp->vec_sol,ksp->vec_sol,ksp,loc_it-1);
247:   return(0);
248: }

250: /*
251:     KSPSolve_FGMRES - This routine applies the FGMRES method.

253:    Input Parameter:
254: .     ksp - the Krylov space object that was set to use fgmres

256:    Output Parameter:
257: .     outits - number of iterations used

259: */

261: PetscErrorCode KSPSolve_FGMRES(KSP ksp)
262: {
264:   PetscInt       cycle_its = 0; /* iterations done in a call to KSPFGMRESCycle */
265:   KSP_FGMRES     *fgmres   = (KSP_FGMRES*)ksp->data;
266:   PetscBool      diagonalscale;

269:   PCGetDiagonalScale(ksp->pc,&diagonalscale);
270:   if (diagonalscale) SETERRQ1(PetscObjectComm((PetscObject)ksp),PETSC_ERR_SUP,"Krylov method %s does not support diagonal scaling",((PetscObject)ksp)->type_name);

272:   PetscObjectSAWsTakeAccess((PetscObject)ksp);
273:   ksp->its = 0;
274:   PetscObjectSAWsGrantAccess((PetscObject)ksp);

276:   /* Compute the initial (NOT preconditioned) residual */
277:   if (!ksp->guess_zero) {
278:     KSPFGMRESResidual(ksp);
279:   } else { /* guess is 0 so residual is F (which is in ksp->vec_rhs) */
280:     VecCopy(ksp->vec_rhs,VEC_VV(0));
281:   }
282:   /* now the residual is in VEC_VV(0) - which is what
283:      KSPFGMRESCycle expects... */

285:   KSPFGMRESCycle(&cycle_its,ksp);
286:   while (!ksp->reason) {
287:     KSPFGMRESResidual(ksp);
288:     if (ksp->its >= ksp->max_it) break;
289:     KSPFGMRESCycle(&cycle_its,ksp);
290:   }
291:   /* mark lack of convergence */
292:   if (ksp->its >= ksp->max_it && !ksp->reason) ksp->reason = KSP_DIVERGED_ITS;
293:   return(0);
294: }

296: extern PetscErrorCode KSPReset_FGMRES(KSP);
297: /*

299:    KSPDestroy_FGMRES - Frees all memory space used by the Krylov method.

301: */
302: PetscErrorCode KSPDestroy_FGMRES(KSP ksp)
303: {

307:   KSPReset_FGMRES(ksp);
308:   PetscObjectComposeFunction((PetscObject)ksp,"KSPFGMRESSetModifyPC_C",NULL);
309:   KSPDestroy_GMRES(ksp);
310:   return(0);
311: }

313: /*
314:     KSPFGMRESBuildSoln - create the solution from the starting vector and the
315:                       current iterates.

317:     Input parameters:
318:         nrs - work area of size it + 1.
319:         vguess  - index of initial guess
320:         vdest - index of result.  Note that vguess may == vdest (replace
321:                 guess with the solution).
322:         it - HH upper triangular part is a block of size (it+1) x (it+1)

324:      This is an internal routine that knows about the FGMRES internals.
325:  */
326: static PetscErrorCode KSPFGMRESBuildSoln(PetscScalar *nrs,Vec vguess,Vec vdest,KSP ksp,PetscInt it)
327: {
328:   PetscScalar    tt;
330:   PetscInt       ii,k,j;
331:   KSP_FGMRES     *fgmres = (KSP_FGMRES*)(ksp->data);

334:   /* Solve for solution vector that minimizes the residual */

336:   /* If it is < 0, no fgmres steps have been performed */
337:   if (it < 0) {
338:     VecCopy(vguess,vdest); /* VecCopy() is smart, exists immediately if vguess == vdest */
339:     return(0);
340:   }

342:   /* so fgmres steps HAVE been performed */

344:   /* solve the upper triangular system - RS is the right side and HH is
345:      the upper triangular matrix  - put soln in nrs */
346:   if (*HH(it,it) != 0.0) {
347:     nrs[it] = *RS(it) / *HH(it,it);
348:   } else {
349:     nrs[it] = 0.0;
350:   }
351:   for (ii=1; ii<=it; ii++) {
352:     k  = it - ii;
353:     tt = *RS(k);
354:     for (j=k+1; j<=it; j++) tt = tt - *HH(k,j) * nrs[j];
355:     nrs[k] = tt / *HH(k,k);
356:   }

358:   /* Accumulate the correction to the soln of the preconditioned prob. in
359:      VEC_TEMP - note that we use the preconditioned vectors  */
360:   VecSet(VEC_TEMP,0.0); /* set VEC_TEMP components to 0 */
361:   VecMAXPY(VEC_TEMP,it+1,nrs,&PREVEC(0));

363:   /* put updated solution into vdest.*/
364:   if (vdest != vguess) {
365:     VecCopy(VEC_TEMP,vdest);
366:     VecAXPY(vdest,1.0,vguess);
367:   } else { /* replace guess with solution */
368:     VecAXPY(vdest,1.0,VEC_TEMP);
369:   }
370:   return(0);
371: }

373: /*

375:     KSPFGMRESUpdateHessenberg - Do the scalar work for the orthogonalization.
376:                             Return new residual.

378:     input parameters:

380: .        ksp -    Krylov space object
381: .        it  -    plane rotations are applied to the (it+1)th column of the
382:                   modified hessenberg (i.e. HH(:,it))
383: .        hapend - PETSC_FALSE not happy breakdown ending.

385:     output parameters:
386: .        res - the new residual

388:  */
389: static PetscErrorCode KSPFGMRESUpdateHessenberg(KSP ksp,PetscInt it,PetscBool hapend,PetscReal *res)
390: {
391:   PetscScalar *hh,*cc,*ss,tt;
392:   PetscInt    j;
393:   KSP_FGMRES  *fgmres = (KSP_FGMRES*)(ksp->data);

396:   hh = HH(0,it);   /* pointer to beginning of column to update - so
397:                       incrementing hh "steps down" the (it+1)th col of HH*/
398:   cc = CC(0);      /* beginning of cosine rotations */
399:   ss = SS(0);      /* beginning of sine rotations */

401:   /* Apply all the previously computed plane rotations to the new column
402:      of the Hessenberg matrix */
403:   /* Note: this uses the rotation [conj(c)  s ; -s   c], c= cos(theta), s= sin(theta),
404:      and some refs have [c   s ; -conj(s)  c] (don't be confused!) */

406:   for (j=1; j<=it; j++) {
407:     tt  = *hh;
408:     *hh = PetscConj(*cc) * tt + *ss * *(hh+1);
409:     hh++;
410:     *hh = *cc++ * *hh - (*ss++ * tt);
411:     /* hh, cc, and ss have all been incremented one by end of loop */
412:   }

414:   /*
415:     compute the new plane rotation, and apply it to:
416:      1) the right-hand-side of the Hessenberg system (RS)
417:         note: it affects RS(it) and RS(it+1)
418:      2) the new column of the Hessenberg matrix
419:         note: it affects HH(it,it) which is currently pointed to
420:         by hh and HH(it+1, it) (*(hh+1))
421:     thus obtaining the updated value of the residual...
422:   */

424:   /* compute new plane rotation */

426:   if (!hapend) {
427:     tt = PetscSqrtScalar(PetscConj(*hh) * *hh + PetscConj(*(hh+1)) * *(hh+1));
428:     if (tt == 0.0) {
429:       ksp->reason = KSP_DIVERGED_NULL;
430:       return(0);
431:     }

433:     *cc = *hh / tt;         /* new cosine value */
434:     *ss = *(hh+1) / tt;        /* new sine value */

436:     /* apply to 1) and 2) */
437:     *RS(it+1) = -(*ss * *RS(it));
438:     *RS(it)   = PetscConj(*cc) * *RS(it);
439:     *hh       = PetscConj(*cc) * *hh + *ss * *(hh+1);

441:     /* residual is the last element (it+1) of right-hand side! */
442:     *res = PetscAbsScalar(*RS(it+1));

444:   } else { /* happy breakdown: HH(it+1, it) = 0, therefore we don't need to apply
445:             another rotation matrix (so RH doesn't change).  The new residual is
446:             always the new sine term times the residual from last time (RS(it)),
447:             but now the new sine rotation would be zero...so the residual should
448:             be zero...so we will multiply "zero" by the last residual.  This might
449:             not be exactly what we want to do here -could just return "zero". */

451:     *res = 0.0;
452:   }
453:   return(0);
454: }

456: /*

458:    KSPFGMRESGetNewVectors - This routine allocates more work vectors, starting from
459:                          VEC_VV(it), and more preconditioned work vectors, starting
460:                          from PREVEC(i).

462: */
463: static PetscErrorCode KSPFGMRESGetNewVectors(KSP ksp,PetscInt it)
464: {
465:   KSP_FGMRES     *fgmres = (KSP_FGMRES*)ksp->data;
466:   PetscInt       nwork   = fgmres->nwork_alloc; /* number of work vector chunks allocated */
467:   PetscInt       nalloc;                      /* number to allocate */
469:   PetscInt       k;

472:   nalloc = fgmres->delta_allocate; /* number of vectors to allocate
473:                                       in a single chunk */

475:   /* Adjust the number to allocate to make sure that we don't exceed the
476:      number of available slots (fgmres->vecs_allocated)*/
477:   if (it + VEC_OFFSET + nalloc >= fgmres->vecs_allocated) {
478:     nalloc = fgmres->vecs_allocated - it - VEC_OFFSET;
479:   }
480:   if (!nalloc) return(0);

482:   fgmres->vv_allocated += nalloc; /* vv_allocated is the number of vectors allocated */

484:   /* work vectors */
485:   KSPCreateVecs(ksp,nalloc,&fgmres->user_work[nwork],0,NULL);
486:   PetscLogObjectParents(ksp,nalloc,fgmres->user_work[nwork]);
487:   for (k=0; k < nalloc; k++) {
488:     fgmres->vecs[it+VEC_OFFSET+k] = fgmres->user_work[nwork][k];
489:   }
490:   /* specify size of chunk allocated */
491:   fgmres->mwork_alloc[nwork] = nalloc;

493:   /* preconditioned vectors */
494:   KSPCreateVecs(ksp,nalloc,&fgmres->prevecs_user_work[nwork],0,NULL);
495:   PetscLogObjectParents(ksp,nalloc,fgmres->prevecs_user_work[nwork]);
496:   for (k=0; k < nalloc; k++) {
497:     fgmres->prevecs[it+k] = fgmres->prevecs_user_work[nwork][k];
498:   }

500:   /* increment the number of work vector chunks */
501:   fgmres->nwork_alloc++;
502:   return(0);
503: }

505: /*

507:    KSPBuildSolution_FGMRES

509:      Input Parameter:
510: .     ksp - the Krylov space object
511: .     ptr-

513:    Output Parameter:
514: .     result - the solution

516:    Note: this calls KSPFGMRESBuildSoln - the same function that KSPFGMRESCycle
517:    calls directly.

519: */
520: PetscErrorCode KSPBuildSolution_FGMRES(KSP ksp,Vec ptr,Vec *result)
521: {
522:   KSP_FGMRES     *fgmres = (KSP_FGMRES*)ksp->data;

526:   if (!ptr) {
527:     if (!fgmres->sol_temp) {
528:       VecDuplicate(ksp->vec_sol,&fgmres->sol_temp);
529:       PetscLogObjectParent((PetscObject)ksp,(PetscObject)fgmres->sol_temp);
530:     }
531:     ptr = fgmres->sol_temp;
532:   }
533:   if (!fgmres->nrs) {
534:     /* allocate the work area */
535:     PetscMalloc1(fgmres->max_k,&fgmres->nrs);
536:     PetscLogObjectMemory((PetscObject)ksp,fgmres->max_k*sizeof(PetscScalar));
537:   }

539:   KSPFGMRESBuildSoln(fgmres->nrs,ksp->vec_sol,ptr,ksp,fgmres->it);
540:   if (result) *result = ptr;
541:   return(0);
542: }

544: PetscErrorCode KSPSetFromOptions_FGMRES(PetscOptionItems *PetscOptionsObject,KSP ksp)
545: {
547:   PetscBool      flg;

550:   KSPSetFromOptions_GMRES(PetscOptionsObject,ksp);
551:   PetscOptionsHead(PetscOptionsObject,"KSP flexible GMRES Options");
552:   PetscOptionsBoolGroupBegin("-ksp_fgmres_modifypcnochange","do not vary the preconditioner","KSPFGMRESSetModifyPC",&flg);
553:   if (flg) {KSPFGMRESSetModifyPC(ksp,KSPFGMRESModifyPCNoChange,NULL,NULL);}
554:   PetscOptionsBoolGroupEnd("-ksp_fgmres_modifypcksp","vary the KSP based preconditioner","KSPFGMRESSetModifyPC",&flg);
555:   if (flg) {KSPFGMRESSetModifyPC(ksp,KSPFGMRESModifyPCKSP,NULL,NULL);}
556:   PetscOptionsTail();
557:   return(0);
558: }

560: typedef PetscErrorCode (*FCN1)(KSP,PetscInt,PetscInt,PetscReal,void*); /* force argument to next function to not be extern C*/
561: typedef PetscErrorCode (*FCN2)(void*);

563: static PetscErrorCode  KSPFGMRESSetModifyPC_FGMRES(KSP ksp,FCN1 fcn,void *ctx,FCN2 d)
564: {
567:   ((KSP_FGMRES*)ksp->data)->modifypc      = fcn;
568:   ((KSP_FGMRES*)ksp->data)->modifydestroy = d;
569:   ((KSP_FGMRES*)ksp->data)->modifyctx     = ctx;
570:   return(0);
571: }

573: PetscErrorCode KSPReset_FGMRES(KSP ksp)
574: {
575:   KSP_FGMRES     *fgmres = (KSP_FGMRES*)ksp->data;
577:   PetscInt       i;

580:   PetscFree (fgmres->prevecs);
581:   if (fgmres->nwork_alloc>0) {
582:     i=0;
583:     /* In the first allocation we allocated VEC_OFFSET fewer vectors in prevecs */
584:     VecDestroyVecs(fgmres->mwork_alloc[i]-VEC_OFFSET,&fgmres->prevecs_user_work[i]);
585:     for (i=1; i<fgmres->nwork_alloc; i++) {
586:       VecDestroyVecs(fgmres->mwork_alloc[i],&fgmres->prevecs_user_work[i]);
587:     }
588:   }
589:   PetscFree(fgmres->prevecs_user_work);
590:   if (fgmres->modifydestroy) {
591:     (*fgmres->modifydestroy)(fgmres->modifyctx);
592:   }
593:   KSPReset_GMRES(ksp);
594:   return(0);
595: }

597: PetscErrorCode  KSPGMRESSetRestart_FGMRES(KSP ksp,PetscInt max_k)
598: {
599:   KSP_FGMRES     *gmres = (KSP_FGMRES*)ksp->data;

603:   if (max_k < 1) SETERRQ(PetscObjectComm((PetscObject)ksp),PETSC_ERR_ARG_OUTOFRANGE,"Restart must be positive");
604:   if (!ksp->setupstage) {
605:     gmres->max_k = max_k;
606:   } else if (gmres->max_k != max_k) {
607:     gmres->max_k    = max_k;
608:     ksp->setupstage = KSP_SETUP_NEW;
609:     /* free the data structures, then create them again */
610:     KSPReset_FGMRES(ksp);
611:   }
612:   return(0);
613: }

615: PetscErrorCode  KSPGMRESGetRestart_FGMRES(KSP ksp,PetscInt *max_k)
616: {
617:   KSP_FGMRES *gmres = (KSP_FGMRES*)ksp->data;

620:   *max_k = gmres->max_k;
621:   return(0);
622: }

624: /*MC
625:      KSPFGMRES - Implements the Flexible Generalized Minimal Residual method.
626:                 developed by Saad with restart

628:    Options Database Keys:
629: +   -ksp_gmres_restart <restart> - the number of Krylov directions to orthogonalize against
630: .   -ksp_gmres_haptol <tol> - sets the tolerance for "happy ending" (exact convergence)
631: .   -ksp_gmres_preallocate - preallocate all the Krylov search directions initially (otherwise groups of
632:                              vectors are allocated as needed)
633: .   -ksp_gmres_classicalgramschmidt - use classical (unmodified) Gram-Schmidt to orthogonalize against the Krylov space (fast) (the default)
634: .   -ksp_gmres_modifiedgramschmidt - use modified Gram-Schmidt in the orthogonalization (more stable, but slower)
635: .   -ksp_gmres_cgs_refinement_type <refine_never,refine_ifneeded,refine_always> - determine if iterative refinement is used to increase the
636:                                    stability of the classical Gram-Schmidt  orthogonalization.
637: .   -ksp_gmres_krylov_monitor - plot the Krylov space generated
638: .   -ksp_fgmres_modifypcnochange - do not change the preconditioner between iterations
639: -   -ksp_fgmres_modifypcksp - modify the preconditioner using KSPFGMRESModifyPCKSP()

641:    Level: beginner

643:     Notes:
644:     See KSPFGMRESSetModifyPC() for how to vary the preconditioner between iterations
645:            Only right preconditioning is supported.

647:     Notes:
648:     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)
649:            be bi-CG-stab with a preconditioner of Jacobi.

651:     Developer Notes:
652:     This object is subclassed off of KSPGMRES

654: .seealso:  KSPCreate(), KSPSetType(), KSPType (for list of available types), KSP, KSPGMRES, KSPLGMRES,
655:            KSPGMRESSetRestart(), KSPGMRESSetHapTol(), KSPGMRESSetPreAllocateVectors(), KSPGMRESSetOrthogonalization(), KSPGMRESGetOrthogonalization(),
656:            KSPGMRESClassicalGramSchmidtOrthogonalization(), KSPGMRESModifiedGramSchmidtOrthogonalization(),
657:            KSPGMRESCGSRefinementType, KSPGMRESSetCGSRefinementType(),  KSPGMRESGetCGSRefinementType(), KSPGMRESMonitorKrylov(), KSPFGMRESSetModifyPC(),
658:            KSPFGMRESModifyPCKSP()

660: M*/

662: PETSC_EXTERN PetscErrorCode KSPCreate_FGMRES(KSP ksp)
663: {
664:   KSP_FGMRES     *fgmres;

668:   PetscNewLog(ksp,&fgmres);

670:   ksp->data                              = (void*)fgmres;
671:   ksp->ops->buildsolution                = KSPBuildSolution_FGMRES;
672:   ksp->ops->setup                        = KSPSetUp_FGMRES;
673:   ksp->ops->solve                        = KSPSolve_FGMRES;
674:   ksp->ops->reset                        = KSPReset_FGMRES;
675:   ksp->ops->destroy                      = KSPDestroy_FGMRES;
676:   ksp->ops->view                         = KSPView_GMRES;
677:   ksp->ops->setfromoptions               = KSPSetFromOptions_FGMRES;
678:   ksp->ops->computeextremesingularvalues = KSPComputeExtremeSingularValues_GMRES;
679:   ksp->ops->computeeigenvalues           = KSPComputeEigenvalues_GMRES;

681:   KSPSetSupportedNorm(ksp,KSP_NORM_UNPRECONDITIONED,PC_RIGHT,3);
682:   KSPSetSupportedNorm(ksp,KSP_NORM_NONE,PC_RIGHT,1);

684:   PetscObjectComposeFunction((PetscObject)ksp,"KSPGMRESSetPreAllocateVectors_C",KSPGMRESSetPreAllocateVectors_GMRES);
685:   PetscObjectComposeFunction((PetscObject)ksp,"KSPGMRESSetOrthogonalization_C",KSPGMRESSetOrthogonalization_GMRES);
686:   PetscObjectComposeFunction((PetscObject)ksp,"KSPGMRESGetOrthogonalization_C",KSPGMRESGetOrthogonalization_GMRES);
687:   PetscObjectComposeFunction((PetscObject)ksp,"KSPGMRESSetRestart_C",KSPGMRESSetRestart_FGMRES);
688:   PetscObjectComposeFunction((PetscObject)ksp,"KSPGMRESGetRestart_C",KSPGMRESGetRestart_FGMRES);
689:   PetscObjectComposeFunction((PetscObject)ksp,"KSPFGMRESSetModifyPC_C",KSPFGMRESSetModifyPC_FGMRES);
690:   PetscObjectComposeFunction((PetscObject)ksp,"KSPGMRESSetCGSRefinementType_C",KSPGMRESSetCGSRefinementType_GMRES);
691:   PetscObjectComposeFunction((PetscObject)ksp,"KSPGMRESGetCGSRefinementType_C",KSPGMRESGetCGSRefinementType_GMRES);

693:   fgmres->haptol         = 1.0e-30;
694:   fgmres->q_preallocate  = 0;
695:   fgmres->delta_allocate = FGMRES_DELTA_DIRECTIONS;
696:   fgmres->orthog         = KSPGMRESClassicalGramSchmidtOrthogonalization;
697:   fgmres->nrs            = NULL;
698:   fgmres->sol_temp       = NULL;
699:   fgmres->max_k          = FGMRES_DEFAULT_MAXK;
700:   fgmres->Rsvd           = NULL;
701:   fgmres->orthogwork     = NULL;
702:   fgmres->modifypc       = KSPFGMRESModifyPCNoChange;
703:   fgmres->modifyctx      = NULL;
704:   fgmres->modifydestroy  = NULL;
705:   fgmres->cgstype        = KSP_GMRES_CGS_REFINE_NEVER;
706:   return(0);
707: }