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);
175:     KSPCheckNorm(ksp,tt);

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

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

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

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

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

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

215:     /* Catch error in happy breakdown and signal convergence and break from loop */
216:     if (hapend) {
217:       if (!ksp->reason) {
218:         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);
219:         else {
220:           ksp->reason = KSP_DIVERGED_BREAKDOWN;
221:           break;
222:         }
223:       }
224:     }
225:   }
226:   /* END OF ITERATION LOOP */
227:   KSPLogResidualHistory(ksp,res_norm);

229:   /*
230:      Monitor if we know that we will not return for a restart */
231:   if (loc_it && (ksp->reason || ksp->its >= ksp->max_it)) {
232:     KSPMonitor(ksp,ksp->its,res_norm);
233:   }

235:   if (itcount) *itcount = loc_it;

237:   /*
238:     Down here we have to solve for the "best" coefficients of the Krylov
239:     columns, add the solution values together, and possibly unwind the
240:     preconditioning from the solution
241:    */

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

247:   KSPFGMRESBuildSoln(RS(0),ksp->vec_sol,ksp->vec_sol,ksp,loc_it-1);
248:   return(0);
249: }

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

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

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

260: */

262: PetscErrorCode KSPSolve_FGMRES(KSP ksp)
263: {
265:   PetscInt       cycle_its = 0; /* iterations done in a call to KSPFGMRESCycle */
266:   KSP_FGMRES     *fgmres   = (KSP_FGMRES*)ksp->data;
267:   PetscBool      diagonalscale;

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

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

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

286:   KSPFGMRESCycle(&cycle_its,ksp);
287:   while (!ksp->reason) {
288:     KSPFGMRESResidual(ksp);
289:     if (ksp->its >= ksp->max_it) break;
290:     KSPFGMRESCycle(&cycle_its,ksp);
291:   }
292:   /* mark lack of convergence */
293:   if (ksp->its >= ksp->max_it && !ksp->reason) ksp->reason = KSP_DIVERGED_ITS;
294:   return(0);
295: }

297: extern PetscErrorCode KSPReset_FGMRES(KSP);
298: /*

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

302: */
303: PetscErrorCode KSPDestroy_FGMRES(KSP ksp)
304: {

308:   KSPReset_FGMRES(ksp);
309:   PetscObjectComposeFunction((PetscObject)ksp,"KSPFGMRESSetModifyPC_C",NULL);
310:   KSPDestroy_GMRES(ksp);
311:   return(0);
312: }

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

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

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

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

337:   /* If it is < 0, no fgmres steps have been performed */
338:   if (it < 0) {
339:     VecCopy(vguess,vdest); /* VecCopy() is smart, exists immediately if vguess == vdest */
340:     return(0);
341:   }

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

345:   /* solve the upper triangular system - RS is the right side and HH is
346:      the upper triangular matrix  - put soln in nrs */
347:   if (*HH(it,it) != 0.0) {
348:     nrs[it] = *RS(it) / *HH(it,it);
349:   } else {
350:     nrs[it] = 0.0;
351:   }
352:   for (ii=1; ii<=it; ii++) {
353:     k  = it - ii;
354:     tt = *RS(k);
355:     for (j=k+1; j<=it; j++) tt = tt - *HH(k,j) * nrs[j];
356:     nrs[k] = tt / *HH(k,k);
357:   }

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

364:   /* put updated solution into vdest.*/
365:   if (vdest != vguess) {
366:     VecCopy(VEC_TEMP,vdest);
367:     VecAXPY(vdest,1.0,vguess);
368:   } else { /* replace guess with solution */
369:     VecAXPY(vdest,1.0,VEC_TEMP);
370:   }
371:   return(0);
372: }

374: /*

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

379:     input parameters:

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

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

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

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

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

407:   for (j=1; j<=it; j++) {
408:     tt  = *hh;
409:     *hh = PetscConj(*cc) * tt + *ss * *(hh+1);
410:     hh++;
411:     *hh = *cc++ * *hh - (*ss++ * tt);
412:     /* hh, cc, and ss have all been incremented one by end of loop */
413:   }

415:   /*
416:     compute the new plane rotation, and apply it to:
417:      1) the right-hand-side of the Hessenberg system (RS)
418:         note: it affects RS(it) and RS(it+1)
419:      2) the new column of the Hessenberg matrix
420:         note: it affects HH(it,it) which is currently pointed to
421:         by hh and HH(it+1, it) (*(hh+1))
422:     thus obtaining the updated value of the residual...
423:   */

425:   /* compute new plane rotation */

427:   if (!hapend) {
428:     tt = PetscSqrtScalar(PetscConj(*hh) * *hh + PetscConj(*(hh+1)) * *(hh+1));
429:     if (tt == 0.0) {
430:       ksp->reason = KSP_DIVERGED_NULL;
431:       return(0);
432:     }

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

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

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

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

452:     *res = 0.0;
453:   }
454:   return(0);
455: }

457: /*

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

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

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

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

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

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

494:   /* preconditioned vectors */
495:   KSPCreateVecs(ksp,nalloc,&fgmres->prevecs_user_work[nwork],0,NULL);
496:   PetscLogObjectParents(ksp,nalloc,fgmres->prevecs_user_work[nwork]);
497:   for (k=0; k < nalloc; k++) {
498:     fgmres->prevecs[it+k] = fgmres->prevecs_user_work[nwork][k];
499:   }

501:   /* increment the number of work vector chunks */
502:   fgmres->nwork_alloc++;
503:   return(0);
504: }

506: /*

508:    KSPBuildSolution_FGMRES

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

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

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

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

527:   if (!ptr) {
528:     if (!fgmres->sol_temp) {
529:       VecDuplicate(ksp->vec_sol,&fgmres->sol_temp);
530:       PetscLogObjectParent((PetscObject)ksp,(PetscObject)fgmres->sol_temp);
531:     }
532:     ptr = fgmres->sol_temp;
533:   }
534:   if (!fgmres->nrs) {
535:     /* allocate the work area */
536:     PetscMalloc1(fgmres->max_k,&fgmres->nrs);
537:     PetscLogObjectMemory((PetscObject)ksp,fgmres->max_k*sizeof(PetscScalar));
538:   }

540:   KSPFGMRESBuildSoln(fgmres->nrs,ksp->vec_sol,ptr,ksp,fgmres->it);
541:   if (result) *result = ptr;
542:   return(0);
543: }

545: PetscErrorCode KSPSetFromOptions_FGMRES(PetscOptionItems *PetscOptionsObject,KSP ksp)
546: {
548:   PetscBool      flg;

551:   KSPSetFromOptions_GMRES(PetscOptionsObject,ksp);
552:   PetscOptionsHead(PetscOptionsObject,"KSP flexible GMRES Options");
553:   PetscOptionsBoolGroupBegin("-ksp_fgmres_modifypcnochange","do not vary the preconditioner","KSPFGMRESSetModifyPC",&flg);
554:   if (flg) {KSPFGMRESSetModifyPC(ksp,KSPFGMRESModifyPCNoChange,NULL,NULL);}
555:   PetscOptionsBoolGroupEnd("-ksp_fgmres_modifypcksp","vary the KSP based preconditioner","KSPFGMRESSetModifyPC",&flg);
556:   if (flg) {KSPFGMRESSetModifyPC(ksp,KSPFGMRESModifyPCKSP,NULL,NULL);}
557:   PetscOptionsTail();
558:   return(0);
559: }

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

564: static PetscErrorCode  KSPFGMRESSetModifyPC_FGMRES(KSP ksp,FCN1 fcn,void *ctx,FCN2 d)
565: {
568:   ((KSP_FGMRES*)ksp->data)->modifypc      = fcn;
569:   ((KSP_FGMRES*)ksp->data)->modifydestroy = d;
570:   ((KSP_FGMRES*)ksp->data)->modifyctx     = ctx;
571:   return(0);
572: }

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

581:   PetscFree (fgmres->prevecs);
582:   if (fgmres->nwork_alloc>0) {
583:     i=0;
584:     /* In the first allocation we allocated VEC_OFFSET fewer vectors in prevecs */
585:     VecDestroyVecs(fgmres->mwork_alloc[i]-VEC_OFFSET,&fgmres->prevecs_user_work[i]);
586:     for (i=1; i<fgmres->nwork_alloc; i++) {
587:       VecDestroyVecs(fgmres->mwork_alloc[i],&fgmres->prevecs_user_work[i]);
588:     }
589:   }
590:   PetscFree(fgmres->prevecs_user_work);
591:   if (fgmres->modifydestroy) {
592:     (*fgmres->modifydestroy)(fgmres->modifyctx);
593:   }
594:   KSPReset_GMRES(ksp);
595:   return(0);
596: }

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

604:   if (max_k < 1) SETERRQ(PetscObjectComm((PetscObject)ksp),PETSC_ERR_ARG_OUTOFRANGE,"Restart must be positive");
605:   if (!ksp->setupstage) {
606:     gmres->max_k = max_k;
607:   } else if (gmres->max_k != max_k) {
608:     gmres->max_k    = max_k;
609:     ksp->setupstage = KSP_SETUP_NEW;
610:     /* free the data structures, then create them again */
611:     KSPReset_FGMRES(ksp);
612:   }
613:   return(0);
614: }

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

621:   *max_k = gmres->max_k;
622:   return(0);
623: }

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

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

642:    Level: beginner

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

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

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

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

661: M*/

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

669:   PetscNewLog(ksp,&fgmres);

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

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

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

694:   fgmres->haptol         = 1.0e-30;
695:   fgmres->q_preallocate  = 0;
696:   fgmres->delta_allocate = FGMRES_DELTA_DIRECTIONS;
697:   fgmres->orthog         = KSPGMRESClassicalGramSchmidtOrthogonalization;
698:   fgmres->nrs            = NULL;
699:   fgmres->sol_temp       = NULL;
700:   fgmres->max_k          = FGMRES_DEFAULT_MAXK;
701:   fgmres->Rsvd           = NULL;
702:   fgmres->orthogwork     = NULL;
703:   fgmres->modifypc       = KSPFGMRESModifyPCNoChange;
704:   fgmres->modifyctx      = NULL;
705:   fgmres->modifydestroy  = NULL;
706:   fgmres->cgstype        = KSP_GMRES_CGS_REFINE_NEVER;
707:   return(0);
708: }