Actual source code: fgmres.c

petsc-master 2014-12-24
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  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>       /*I  "petscksp.h"  I*/
 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: */
 34: PetscErrorCode    KSPSetUp_FGMRES(KSP ksp)
 35: {
 37:   PetscInt       max_k,k;
 38:   KSP_FGMRES     *fgmres = (KSP_FGMRES*)ksp->data;

 41:   max_k = fgmres->max_k;

 43:   KSPSetUp_GMRES(ksp);

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

 49:   KSPCreateVecs(ksp,fgmres->vv_allocated,&fgmres->prevecs_user_work[0],0,NULL);
 50:   PetscLogObjectParents(ksp,fgmres->vv_allocated,fgmres->prevecs_user_work[0]);
 51:   for (k=0; k < fgmres->vv_allocated; k++) {
 52:     fgmres->prevecs[k] = fgmres->prevecs_user_work[0][k];
 53:   }
 54:   return(0);
 55: }

 57: /*
 58:     KSPFGMRESResidual - This routine computes the initial residual (NOT PRECONDITIONED)
 59: */
 62: static PetscErrorCode KSPFGMRESResidual(KSP ksp)
 63: {
 64:   KSP_FGMRES     *fgmres = (KSP_FGMRES*)(ksp->data);
 65:   Mat            Amat,Pmat;

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

 71:   /* put A*x into VEC_TEMP */
 72:   MatMult(Amat,ksp->vec_sol,VEC_TEMP);
 73:   /* now put residual (-A*x + f) into vec_vv(0) */
 74:   VecWAXPY(VEC_VV(0),-1.0,VEC_TEMP,ksp->vec_rhs);
 75:   return(0);
 76: }

 78: /*

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

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

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


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


 96:  */
 99: PetscErrorCode KSPFGMRESCycle(PetscInt *itcount,KSP ksp)
100: {

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

112:   /* Number of pseudo iterations since last restart is the number
113:      of prestart directions */
114:   loc_it = 0;

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

122:   /* initial residual is in VEC_VV(0)  - compute its norm*/
123:   VecNorm(VEC_VV(0),NORM_2,&res_norm);

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

129:   ksp->rnorm = res_norm;
130:   KSPLogResidualHistory(ksp,res_norm);
131:   KSPMonitor(ksp,ksp->its,res_norm);

133:   /* check for the convergence - maybe the current guess is good enough */
134:   (*ksp->converged)(ksp,ksp->its,res_norm,&ksp->reason,ksp->cnvP);
135:   if (ksp->reason) {
136:     if (itcount) *itcount = 0;
137:     return(0);
138:   }

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

143:   /* MAIN ITERATION LOOP BEGINNING*/
144:   /* keep iterating until we have converged OR generated the max number
145:      of directions OR reached the max number of iterations for the method */
146:   while (!ksp->reason && loc_it < max_k && ksp->its < ksp->max_it) {
147:     if (loc_it) {
148:       KSPLogResidualHistory(ksp,res_norm);
149:       KSPMonitor(ksp,ksp->its,res_norm);
150:     }
151:     fgmres->it = (loc_it - 1);

153:     /* see if more space is needed for work vectors */
154:     if (fgmres->vv_allocated <= loc_it + VEC_OFFSET + 1) {
155:       KSPFGMRESGetNewVectors(ksp,loc_it+1);
156:       /* (loc_it+1) is passed in as number of the first vector that should
157:          be allocated */
158:     }

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


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

170:     PCGetOperators(ksp->pc,&Amat,&Pmat);
171:     /* Multiply preconditioned vector by operator - put in VEC_VV(loc_it+1) */
172:     MatMult(Amat,PREVEC(loc_it),VEC_VV(1+loc_it));


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

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

182:     *HH(loc_it+1,loc_it)  = tt;
183:     *HES(loc_it+1,loc_it) = tt;

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


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

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

214:     PetscObjectSAWsTakeAccess((PetscObject)ksp);
215:     ksp->its++;
216:     ksp->rnorm = res_norm;
217:     PetscObjectSAWsGrantAccess((PetscObject)ksp);

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

221:     /* Catch error in happy breakdown and signal convergence and break from loop */
222:     if (hapend) {
223:       if (!ksp->reason) {
224:         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);
225:         else {
226:           ksp->reason = KSP_DIVERGED_BREAKDOWN;
227:           break;
228:         }
229:       }
230:     }
231:   }
232:   /* END OF ITERATION LOOP */
233:   KSPLogResidualHistory(ksp,res_norm);

235:   /*
236:      Monitor if we know that we will not return for a restart */
237:   if (loc_it && (ksp->reason || ksp->its >= ksp->max_it)) {
238:     KSPMonitor(ksp,ksp->its,res_norm);
239:   }

241:   if (itcount) *itcount = loc_it;

243:   /*
244:     Down here we have to solve for the "best" coefficients of the Krylov
245:     columns, add the solution values together, and possibly unwind the
246:     preconditioning from the solution
247:    */

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

253:   KSPFGMRESBuildSoln(RS(0),ksp->vec_sol,ksp->vec_sol,ksp,loc_it-1);
254:   return(0);
255: }

257: /*
258:     KSPSolve_FGMRES - This routine applies the FGMRES method.


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

264:    Output Parameter:
265: .     outits - number of iterations used

267: */

271: PetscErrorCode KSPSolve_FGMRES(KSP ksp)
272: {
274:   PetscInt       cycle_its = 0; /* iterations done in a call to KSPFGMRESCycle */
275:   KSP_FGMRES     *fgmres   = (KSP_FGMRES*)ksp->data;
276:   PetscBool      diagonalscale;

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

282:   PetscObjectSAWsTakeAccess((PetscObject)ksp);
283:   ksp->its = 0;
284:   PetscObjectSAWsGrantAccess((PetscObject)ksp);

286:   /* Compute the initial (NOT preconditioned) residual */
287:   if (!ksp->guess_zero) {
288:     KSPFGMRESResidual(ksp);
289:   } else { /* guess is 0 so residual is F (which is in ksp->vec_rhs) */
290:     VecCopy(ksp->vec_rhs,VEC_VV(0));
291:   }
292:   /* now the residual is in VEC_VV(0) - which is what
293:      KSPFGMRESCycle expects... */

295:   KSPFGMRESCycle(&cycle_its,ksp);
296:   while (!ksp->reason) {
297:     KSPFGMRESResidual(ksp);
298:     if (ksp->its >= ksp->max_it) break;
299:     KSPFGMRESCycle(&cycle_its,ksp);
300:   }
301:   /* mark lack of convergence */
302:   if (ksp->its >= ksp->max_it && !ksp->reason) ksp->reason = KSP_DIVERGED_ITS;
303:   return(0);
304: }

306: extern PetscErrorCode KSPReset_FGMRES(KSP);
307: /*

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

311: */
314: PetscErrorCode KSPDestroy_FGMRES(KSP ksp)
315: {

319:   KSPReset_FGMRES(ksp);
320:   PetscObjectComposeFunction((PetscObject)ksp,"KSPFGMRESSetModifyPC_C",NULL);
321:   KSPDestroy_GMRES(ksp);
322:   return(0);
323: }

325: /*
326:     KSPFGMRESBuildSoln - create the solution from the starting vector and the
327:                       current iterates.

329:     Input parameters:
330:         nrs - work area of size it + 1.
331:         vguess  - index of initial guess
332:         vdest - index of result.  Note that vguess may == vdest (replace
333:                 guess with the solution).
334:         it - HH upper triangular part is a block of size (it+1) x (it+1)

336:      This is an internal routine that knows about the FGMRES internals.
337:  */
340: static PetscErrorCode KSPFGMRESBuildSoln(PetscScalar *nrs,Vec vguess,Vec vdest,KSP ksp,PetscInt it)
341: {
342:   PetscScalar    tt;
344:   PetscInt       ii,k,j;
345:   KSP_FGMRES     *fgmres = (KSP_FGMRES*)(ksp->data);

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

350:   /* If it is < 0, no fgmres steps have been performed */
351:   if (it < 0) {
352:     VecCopy(vguess,vdest); /* VecCopy() is smart, exists immediately if vguess == vdest */
353:     return(0);
354:   }

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

358:   /* solve the upper triangular system - RS is the right side and HH is
359:      the upper triangular matrix  - put soln in nrs */
360:   if (*HH(it,it) != 0.0) {
361:     nrs[it] = *RS(it) / *HH(it,it);
362:   } else {
363:     nrs[it] = 0.0;
364:   }
365:   for (ii=1; ii<=it; ii++) {
366:     k  = it - ii;
367:     tt = *RS(k);
368:     for (j=k+1; j<=it; j++) tt = tt - *HH(k,j) * nrs[j];
369:     nrs[k] = tt / *HH(k,k);
370:   }

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

377:   /* put updated solution into vdest.*/
378:   if (vdest != vguess) {
379:     VecCopy(VEC_TEMP,vdest);
380:     VecAXPY(vdest,1.0,vguess);
381:   } else { /* replace guess with solution */
382:     VecAXPY(vdest,1.0,VEC_TEMP);
383:   }
384:   return(0);
385: }

387: /*

389:     KSPFGMRESUpdateHessenberg - Do the scalar work for the orthogonalization.
390:                             Return new residual.

392:     input parameters:

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

399:     output parameters:
400: .        res - the new residual

402:  */
405: static PetscErrorCode KSPFGMRESUpdateHessenberg(KSP ksp,PetscInt it,PetscBool hapend,PetscReal *res)
406: {
407:   PetscScalar *hh,*cc,*ss,tt;
408:   PetscInt    j;
409:   KSP_FGMRES  *fgmres = (KSP_FGMRES*)(ksp->data);

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

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

422:   for (j=1; j<=it; j++) {
423:     tt  = *hh;
424:     *hh = PetscConj(*cc) * tt + *ss * *(hh+1);
425:     hh++;
426:     *hh = *cc++ * *hh - (*ss++ * tt);
427:     /* hh, cc, and ss have all been incremented one by end of loop */
428:   }

430:   /*
431:     compute the new plane rotation, and apply it to:
432:      1) the right-hand-side of the Hessenberg system (RS)
433:         note: it affects RS(it) and RS(it+1)
434:      2) the new column of the Hessenberg matrix
435:         note: it affects HH(it,it) which is currently pointed to
436:         by hh and HH(it+1, it) (*(hh+1))
437:     thus obtaining the updated value of the residual...
438:   */

440:   /* compute new plane rotation */

442:   if (!hapend) {
443:     tt = PetscSqrtScalar(PetscConj(*hh) * *hh + PetscConj(*(hh+1)) * *(hh+1));
444:     if (tt == 0.0) {
445:       ksp->reason = KSP_DIVERGED_NULL;
446:       return(0);
447:     }

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

452:     /* apply to 1) and 2) */
453:     *RS(it+1) = -(*ss * *RS(it));
454:     *RS(it)   = PetscConj(*cc) * *RS(it);
455:     *hh       = PetscConj(*cc) * *hh + *ss * *(hh+1);

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

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

467:     *res = 0.0;
468:   }
469:   return(0);
470: }

472: /*

474:    KSPFGMRESGetNewVectors - This routine allocates more work vectors, starting from
475:                          VEC_VV(it), and more preconditioned work vectors, starting
476:                          from PREVEC(i).

478: */
481: static PetscErrorCode KSPFGMRESGetNewVectors(KSP ksp,PetscInt it)
482: {
483:   KSP_FGMRES     *fgmres = (KSP_FGMRES*)ksp->data;
484:   PetscInt       nwork   = fgmres->nwork_alloc; /* number of work vector chunks allocated */
485:   PetscInt       nalloc;                      /* number to allocate */
487:   PetscInt       k;

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

493:   /* Adjust the number to allocate to make sure that we don't exceed the
494:      number of available slots (fgmres->vecs_allocated)*/
495:   if (it + VEC_OFFSET + nalloc >= fgmres->vecs_allocated) {
496:     nalloc = fgmres->vecs_allocated - it - VEC_OFFSET;
497:   }
498:   if (!nalloc) return(0);

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

502:   /* work vectors */
503:   KSPCreateVecs(ksp,nalloc,&fgmres->user_work[nwork],0,NULL);
504:   PetscLogObjectParents(ksp,nalloc,fgmres->user_work[nwork]);
505:   for (k=0; k < nalloc; k++) {
506:     fgmres->vecs[it+VEC_OFFSET+k] = fgmres->user_work[nwork][k];
507:   }
508:   /* specify size of chunk allocated */
509:   fgmres->mwork_alloc[nwork] = nalloc;

511:   /* preconditioned vectors */
512:   KSPCreateVecs(ksp,nalloc,&fgmres->prevecs_user_work[nwork],0,NULL);
513:   PetscLogObjectParents(ksp,nalloc,fgmres->prevecs_user_work[nwork]);
514:   for (k=0; k < nalloc; k++) {
515:     fgmres->prevecs[it+VEC_OFFSET+k] = fgmres->prevecs_user_work[nwork][k];
516:   }

518:   /* increment the number of work vector chunks */
519:   fgmres->nwork_alloc++;
520:   return(0);
521: }

523: /*

525:    KSPBuildSolution_FGMRES

527:      Input Parameter:
528: .     ksp - the Krylov space object
529: .     ptr-

531:    Output Parameter:
532: .     result - the solution

534:    Note: this calls KSPFGMRESBuildSoln - the same function that KSPFGMRESCycle
535:    calls directly.

537: */
540: PetscErrorCode KSPBuildSolution_FGMRES(KSP ksp,Vec ptr,Vec *result)
541: {
542:   KSP_FGMRES     *fgmres = (KSP_FGMRES*)ksp->data;

546:   if (!ptr) {
547:     if (!fgmres->sol_temp) {
548:       VecDuplicate(ksp->vec_sol,&fgmres->sol_temp);
549:       PetscLogObjectParent((PetscObject)ksp,(PetscObject)fgmres->sol_temp);
550:     }
551:     ptr = fgmres->sol_temp;
552:   }
553:   if (!fgmres->nrs) {
554:     /* allocate the work area */
555:     PetscMalloc1(fgmres->max_k,&fgmres->nrs);
556:     PetscLogObjectMemory((PetscObject)ksp,fgmres->max_k*sizeof(PetscScalar));
557:   }

559:   KSPFGMRESBuildSoln(fgmres->nrs,ksp->vec_sol,ptr,ksp,fgmres->it);
560:   if (result) *result = ptr;
561:   return(0);
562: }

566: PetscErrorCode KSPSetFromOptions_FGMRES(KSP ksp)
567: {
569:   PetscBool      flg;

572:   KSPSetFromOptions_GMRES(ksp);
573:   PetscOptionsHead("KSP flexible GMRES Options");
574:   PetscOptionsBoolGroupBegin("-ksp_fgmres_modifypcnochange","do not vary the preconditioner","KSPFGMRESSetModifyPC",&flg);
575:   if (flg) {KSPFGMRESSetModifyPC(ksp,KSPFGMRESModifyPCNoChange,0,0);}
576:   PetscOptionsBoolGroupEnd("-ksp_fgmres_modifypcksp","vary the KSP based preconditioner","KSPFGMRESSetModifyPC",&flg);
577:   if (flg) {KSPFGMRESSetModifyPC(ksp,KSPFGMRESModifyPCKSP,0,0);}
578:   PetscOptionsTail();
579:   return(0);
580: }

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

587: static PetscErrorCode  KSPFGMRESSetModifyPC_FGMRES(KSP ksp,FCN1 fcn,void *ctx,FCN2 d)
588: {
591:   ((KSP_FGMRES*)ksp->data)->modifypc      = fcn;
592:   ((KSP_FGMRES*)ksp->data)->modifydestroy = d;
593:   ((KSP_FGMRES*)ksp->data)->modifyctx     = ctx;
594:   return(0);
595: }


600: PetscErrorCode KSPReset_FGMRES(KSP ksp)
601: {
602:   KSP_FGMRES     *fgmres = (KSP_FGMRES*)ksp->data;
604:   PetscInt       i;

607:   PetscFree (fgmres->prevecs);
608:   for (i=0; i<fgmres->nwork_alloc; i++) {
609:     VecDestroyVecs(fgmres->mwork_alloc[i],&fgmres->prevecs_user_work[i]);
610:   }
611:   PetscFree(fgmres->prevecs_user_work);
612:   if (fgmres->modifydestroy) {
613:     (*fgmres->modifydestroy)(fgmres->modifyctx);
614:   }
615:   KSPReset_GMRES(ksp);
616:   return(0);
617: }

621: PetscErrorCode  KSPGMRESSetRestart_FGMRES(KSP ksp,PetscInt max_k)
622: {
623:   KSP_FGMRES     *gmres = (KSP_FGMRES*)ksp->data;

627:   if (max_k < 1) SETERRQ(PetscObjectComm((PetscObject)ksp),PETSC_ERR_ARG_OUTOFRANGE,"Restart must be positive");
628:   if (!ksp->setupstage) {
629:     gmres->max_k = max_k;
630:   } else if (gmres->max_k != max_k) {
631:     gmres->max_k    = max_k;
632:     ksp->setupstage = KSP_SETUP_NEW;
633:     /* free the data structures, then create them again */
634:     KSPReset_FGMRES(ksp);
635:   }
636:   return(0);
637: }

641: PetscErrorCode  KSPGMRESGetRestart_FGMRES(KSP ksp,PetscInt *max_k)
642: {
643:   KSP_FGMRES *gmres = (KSP_FGMRES*)ksp->data;

646:   *max_k = gmres->max_k;
647:   return(0);
648: }

650: /*MC
651:      KSPFGMRES - Implements the Flexible Generalized Minimal Residual method.
652:                 developed by Saad with restart


655:    Options Database Keys:
656: +   -ksp_gmres_restart <restart> - the number of Krylov directions to orthogonalize against
657: .   -ksp_gmres_haptol <tol> - sets the tolerance for "happy ending" (exact convergence)
658: .   -ksp_gmres_preallocate - preallocate all the Krylov search directions initially (otherwise groups of
659:                              vectors are allocated as needed)
660: .   -ksp_gmres_classicalgramschmidt - use classical (unmodified) Gram-Schmidt to orthogonalize against the Krylov space (fast) (the default)
661: .   -ksp_gmres_modifiedgramschmidt - use modified Gram-Schmidt in the orthogonalization (more stable, but slower)
662: .   -ksp_gmres_cgs_refinement_type <never,ifneeded,always> - determine if iterative refinement is used to increase the
663:                                    stability of the classical Gram-Schmidt  orthogonalization.
664: .   -ksp_gmres_krylov_monitor - plot the Krylov space generated
665: .   -ksp_fgmres_modifypcnochange - do not change the preconditioner between iterations
666: -   -ksp_fgmres_modifypcksp - modify the preconditioner using KSPFGMRESModifyPCKSP()

668:    Level: beginner

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

673:     Notes: 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)
674:            be bi-CG-stab with a preconditioner of Jacobi.

676:     Developer Notes: This object is subclassed off of KSPGMRES

678: .seealso:  KSPCreate(), KSPSetType(), KSPType (for list of available types), KSP, KSPGMRES, KSPLGMRES,
679:            KSPGMRESSetRestart(), KSPGMRESSetHapTol(), KSPGMRESSetPreAllocateVectors(), KSPGMRESSetOrthogonalization(), KSPGMRESGetOrthogonalization(),
680:            KSPGMRESClassicalGramSchmidtOrthogonalization(), KSPGMRESModifiedGramSchmidtOrthogonalization(),
681:            KSPGMRESCGSRefinementType, KSPGMRESSetCGSRefinementType(),  KSPGMRESGetCGSRefinementType(), KSPGMRESMonitorKrylov(), KSPFGMRESSetModifyPC(),
682:            KSPFGMRESModifyPCKSP()

684: M*/

688: PETSC_EXTERN PetscErrorCode KSPCreate_FGMRES(KSP ksp)
689: {
690:   KSP_FGMRES     *fgmres;

694:   PetscNewLog(ksp,&fgmres);

696:   ksp->data                              = (void*)fgmres;
697:   ksp->ops->buildsolution                = KSPBuildSolution_FGMRES;
698:   ksp->ops->setup                        = KSPSetUp_FGMRES;
699:   ksp->ops->solve                        = KSPSolve_FGMRES;
700:   ksp->ops->reset                        = KSPReset_FGMRES;
701:   ksp->ops->destroy                      = KSPDestroy_FGMRES;
702:   ksp->ops->view                         = KSPView_GMRES;
703:   ksp->ops->setfromoptions               = KSPSetFromOptions_FGMRES;
704:   ksp->ops->computeextremesingularvalues = KSPComputeExtremeSingularValues_GMRES;
705:   ksp->ops->computeeigenvalues           = KSPComputeEigenvalues_GMRES;

707:   KSPSetSupportedNorm(ksp,KSP_NORM_UNPRECONDITIONED,PC_RIGHT,3);
708:   KSPSetSupportedNorm(ksp,KSP_NORM_NONE,PC_LEFT,0);

710:   PetscObjectComposeFunction((PetscObject)ksp,"KSPGMRESSetPreAllocateVectors_C",KSPGMRESSetPreAllocateVectors_GMRES);
711:   PetscObjectComposeFunction((PetscObject)ksp,"KSPGMRESSetOrthogonalization_C",KSPGMRESSetOrthogonalization_GMRES);
712:   PetscObjectComposeFunction((PetscObject)ksp,"KSPGMRESGetOrthogonalization_C",KSPGMRESGetOrthogonalization_GMRES);
713:   PetscObjectComposeFunction((PetscObject)ksp,"KSPGMRESSetRestart_C",KSPGMRESSetRestart_FGMRES);
714:   PetscObjectComposeFunction((PetscObject)ksp,"KSPGMRESGetRestart_C",KSPGMRESGetRestart_FGMRES);
715:   PetscObjectComposeFunction((PetscObject)ksp,"KSPFGMRESSetModifyPC_C",KSPFGMRESSetModifyPC_FGMRES);
716:   PetscObjectComposeFunction((PetscObject)ksp,"KSPGMRESSetCGSRefinementType_C",KSPGMRESSetCGSRefinementType_GMRES);
717:   PetscObjectComposeFunction((PetscObject)ksp,"KSPGMRESGetCGSRefinementType_C",KSPGMRESGetCGSRefinementType_GMRES);


720:   fgmres->haptol         = 1.0e-30;
721:   fgmres->q_preallocate  = 0;
722:   fgmres->delta_allocate = FGMRES_DELTA_DIRECTIONS;
723:   fgmres->orthog         = KSPGMRESClassicalGramSchmidtOrthogonalization;
724:   fgmres->nrs            = 0;
725:   fgmres->sol_temp       = 0;
726:   fgmres->max_k          = FGMRES_DEFAULT_MAXK;
727:   fgmres->Rsvd           = 0;
728:   fgmres->orthogwork     = 0;
729:   fgmres->modifypc       = KSPFGMRESModifyPCNoChange;
730:   fgmres->modifyctx      = NULL;
731:   fgmres->modifydestroy  = NULL;
732:   fgmres->cgstype        = KSP_GMRES_CGS_REFINE_NEVER;
733:   return(0);
734: }