Actual source code: itfunc.c
petsc-3.15.0 2021-03-30
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      1: /*
      2:       Interface KSP routines that the user calls.
      3: */

      5: #include <petsc/private/kspimpl.h>
      6: #include <petsc/private/matimpl.h>
      7: #include <petscdm.h>

      9: PETSC_STATIC_INLINE PetscErrorCode ObjectView(PetscObject obj, PetscViewer viewer, PetscViewerFormat format)
     10: {

     13:   PetscViewerPushFormat(viewer, format);
     14:   PetscObjectView(obj, viewer);
     15:   PetscViewerPopFormat(viewer);
     16:   return(0);
     17: }

     19: /*@
     20:    KSPComputeExtremeSingularValues - Computes the extreme singular values
     21:    for the preconditioned operator. Called after or during KSPSolve().

     23:    Not Collective

     25:    Input Parameter:
     26: .  ksp - iterative context obtained from KSPCreate()

     28:    Output Parameters:
     29: .  emin, emax - extreme singular values

     31:    Options Database Keys:
     32: .  -ksp_view_singularvalues - compute extreme singular values and print when KSPSolve completes.

     34:    Notes:
     35:    One must call KSPSetComputeSingularValues() before calling KSPSetUp()
     36:    (or use the option -ksp_view_eigenvalues) in order for this routine to work correctly.

     38:    Many users may just want to use the monitoring routine
     39:    KSPMonitorSingularValue() (which can be set with option -ksp_monitor_singular_value)
     40:    to print the extreme singular values at each iteration of the linear solve.

     42:    Estimates of the smallest singular value may be very inaccurate, especially if the Krylov method has not converged.
     43:    The largest singular value is usually accurate to within a few percent if the method has converged, but is still not
     44:    intended for eigenanalysis.

     46:    Disable restarts if using KSPGMRES, otherwise this estimate will only be using those iterations after the last
     47:    restart. See KSPGMRESSetRestart() for more details.

     49:    Level: advanced

     51: .seealso: KSPSetComputeSingularValues(), KSPMonitorSingularValue(), KSPComputeEigenvalues(), KSP
     52: @*/
     53: PetscErrorCode  KSPComputeExtremeSingularValues(KSP ksp,PetscReal *emax,PetscReal *emin)
     54: {

     61:   if (!ksp->calc_sings) SETERRQ(PetscObjectComm((PetscObject)ksp),4,"Singular values not requested before KSPSetUp()");

     63:   if (ksp->ops->computeextremesingularvalues) {
     64:     (*ksp->ops->computeextremesingularvalues)(ksp,emax,emin);
     65:   } else {
     66:     *emin = -1.0;
     67:     *emax = -1.0;
     68:   }
     69:   return(0);
     70: }

     72: /*@
     73:    KSPComputeEigenvalues - Computes the extreme eigenvalues for the
     74:    preconditioned operator. Called after or during KSPSolve().

     76:    Not Collective

     78:    Input Parameters:
     79: +  ksp - iterative context obtained from KSPCreate()
     80: -  n - size of arrays r and c. The number of eigenvalues computed (neig) will, in
     81:        general, be less than this.

     83:    Output Parameters:
     84: +  r - real part of computed eigenvalues, provided by user with a dimension of at least n
     85: .  c - complex part of computed eigenvalues, provided by user with a dimension of at least n
     86: -  neig - actual number of eigenvalues computed (will be less than or equal to n)

     88:    Options Database Keys:
     89: .  -ksp_view_eigenvalues - Prints eigenvalues to stdout

     91:    Notes:
     92:    The number of eigenvalues estimated depends on the size of the Krylov space
     93:    generated during the KSPSolve() ; for example, with
     94:    CG it corresponds to the number of CG iterations, for GMRES it is the number
     95:    of GMRES iterations SINCE the last restart. Any extra space in r[] and c[]
     96:    will be ignored.

     98:    KSPComputeEigenvalues() does not usually provide accurate estimates; it is
     99:    intended only for assistance in understanding the convergence of iterative
    100:    methods, not for eigenanalysis. For accurate computation of eigenvalues we recommend using
    101:    the excellent package SLEPc.

    103:    One must call KSPSetComputeEigenvalues() before calling KSPSetUp()
    104:    in order for this routine to work correctly.

    106:    Many users may just want to use the monitoring routine
    107:    KSPMonitorSingularValue() (which can be set with option -ksp_monitor_singular_value)
    108:    to print the singular values at each iteration of the linear solve.

    110:    Level: advanced

    112: .seealso: KSPSetComputeSingularValues(), KSPMonitorSingularValue(), KSPComputeExtremeSingularValues(), KSP
    113: @*/
    114: PetscErrorCode  KSPComputeEigenvalues(KSP ksp,PetscInt n,PetscReal r[],PetscReal c[],PetscInt *neig)
    115: {

    122:   if (n<0) SETERRQ(PetscObjectComm((PetscObject)ksp),PETSC_ERR_ARG_OUTOFRANGE,"Requested < 0 Eigenvalues");
    124:   if (!ksp->calc_sings) SETERRQ(PetscObjectComm((PetscObject)ksp),4,"Eigenvalues not requested before KSPSetUp()");

    126:   if (n && ksp->ops->computeeigenvalues) {
    127:     (*ksp->ops->computeeigenvalues)(ksp,n,r,c,neig);
    128:   } else {
    129:     *neig = 0;
    130:   }
    131:   return(0);
    132: }

    134: /*@
    135:    KSPComputeRitz - Computes the Ritz or harmonic Ritz pairs associated to the
    136:    smallest or largest in modulus, for the preconditioned operator.
    137:    Called after KSPSolve().

    139:    Not Collective

    141:    Input Parameters:
    142: +  ksp   - iterative context obtained from KSPCreate()
    143: .  ritz  - PETSC_TRUE or PETSC_FALSE for ritz pairs or harmonic Ritz pairs, respectively
    144: .  small - PETSC_TRUE or PETSC_FALSE for smallest or largest (harmonic) Ritz values, respectively
    145: -  nrit  - number of (harmonic) Ritz pairs to compute

    147:    Output Parameters:
    148: +  nrit  - actual number of computed (harmonic) Ritz pairs
    149: .  S     - multidimensional vector with Ritz vectors
    150: .  tetar - real part of the Ritz values
    151: -  tetai - imaginary part of the Ritz values

    153:    Notes:
    154:    -For GMRES, the (harmonic) Ritz pairs are computed from the Hessenberg matrix obtained during
    155:    the last complete cycle, or obtained at the end of the solution if the method is stopped before
    156:    a restart. Then, the number of actual (harmonic) Ritz pairs computed is less or equal to the restart
    157:    parameter for GMRES if a complete cycle has been performed or less or equal to the number of GMRES
    158:    iterations.
    159:    -Moreover, for real matrices, the (harmonic) Ritz pairs are possibly complex-valued. In such a case,
    160:    the routine selects the complex (harmonic) Ritz value and its conjugate, and two successive columns of S
    161:    are equal to the real and the imaginary parts of the associated vectors.
    162:    -the (harmonic) Ritz pairs are given in order of increasing (harmonic) Ritz values in modulus
    163:    -this is currently not implemented when PETSc is built with complex numbers

    165:    One must call KSPSetComputeRitz() before calling KSPSetUp()
    166:    in order for this routine to work correctly.

    168:    Level: advanced

    170: .seealso: KSPSetComputeRitz(), KSP
    171: @*/
    172: PetscErrorCode  KSPComputeRitz(KSP ksp,PetscBool ritz,PetscBool small,PetscInt *nrit,Vec S[],PetscReal tetar[],PetscReal tetai[])
    173: {

    178:   if (!ksp->calc_ritz) SETERRQ(PetscObjectComm((PetscObject)ksp),4,"Ritz pairs not requested before KSPSetUp()");
    179:   if (ksp->ops->computeritz) {(*ksp->ops->computeritz)(ksp,ritz,small,nrit,S,tetar,tetai);}
    180:   return(0);
    181: }
    182: /*@
    183:    KSPSetUpOnBlocks - Sets up the preconditioner for each block in
    184:    the block Jacobi, block Gauss-Seidel, and overlapping Schwarz
    185:    methods.

    187:    Collective on ksp

    189:    Input Parameter:
    190: .  ksp - the KSP context

    192:    Notes:
    193:    KSPSetUpOnBlocks() is a routine that the user can optinally call for
    194:    more precise profiling (via -log_view) of the setup phase for these
    195:    block preconditioners.  If the user does not call KSPSetUpOnBlocks(),
    196:    it will automatically be called from within KSPSolve().

    198:    Calling KSPSetUpOnBlocks() is the same as calling PCSetUpOnBlocks()
    199:    on the PC context within the KSP context.

    201:    Level: advanced

    203: .seealso: PCSetUpOnBlocks(), KSPSetUp(), PCSetUp(), KSP
    204: @*/
    205: PetscErrorCode  KSPSetUpOnBlocks(KSP ksp)
    206: {
    207:   PC             pc;
    209:   PCFailedReason pcreason;

    213:   KSPGetPC(ksp,&pc);
    214:   PCSetUpOnBlocks(pc);
    215:   PCGetFailedReasonRank(pc,&pcreason);
    216:   /* TODO: this code was wrong and is still wrong, there is no way to propogate the failure to all processes; their is no code to handle a ksp->reason on only some ranks */
    217:   if (pcreason) {
    218:     ksp->reason = KSP_DIVERGED_PC_FAILED;
    219:   }
    220:   return(0);
    221: }

    223: /*@
    224:    KSPSetReusePreconditioner - reuse the current preconditioner, do not construct a new one even if the operator changes

    226:    Collective on ksp

    228:    Input Parameters:
    229: +  ksp   - iterative context obtained from KSPCreate()
    230: -  flag - PETSC_TRUE to reuse the current preconditioner

    232:    Level: intermediate

    234: .seealso: KSPCreate(), KSPSolve(), KSPDestroy(), PCSetReusePreconditioner(), KSP
    235: @*/
    236: PetscErrorCode  KSPSetReusePreconditioner(KSP ksp,PetscBool flag)
    237: {
    238:   PC             pc;

    243:   KSPGetPC(ksp,&pc);
    244:   PCSetReusePreconditioner(pc,flag);
    245:   return(0);
    246: }

    248: /*@
    249:    KSPGetReusePreconditioner - Determines if the KSP reuses the current preconditioner even if the operator in the preconditioner has changed.

    251:    Collective on ksp

    253:    Input Parameters:
    254: .  ksp   - iterative context obtained from KSPCreate()

    256:    Output Parameters:
    257: .  flag - the boolean flag

    259:    Level: intermediate

    261: .seealso: KSPCreate(), KSPSolve(), KSPDestroy(), KSPSetReusePreconditioner(), KSP
    262: @*/
    263: PetscErrorCode  KSPGetReusePreconditioner(KSP ksp,PetscBool *flag)
    264: {

    270:   *flag = PETSC_FALSE;
    271:   if (ksp->pc) {
    272:     PCGetReusePreconditioner(ksp->pc,flag);
    273:   }
    274:   return(0);
    275: }

    277: /*@
    278:    KSPSetSkipPCSetFromOptions - prevents KSPSetFromOptions() from call PCSetFromOptions(). This is used if the same PC is shared by more than one KSP so its options are not resetable for each KSP

    280:    Collective on ksp

    282:    Input Parameters:
    283: +  ksp   - iterative context obtained from KSPCreate()
    284: -  flag - PETSC_TRUE to skip calling the PCSetFromOptions()

    286:    Level: intermediate

    288: .seealso: KSPCreate(), KSPSolve(), KSPDestroy(), PCSetReusePreconditioner(), KSP
    289: @*/
    290: PetscErrorCode  KSPSetSkipPCSetFromOptions(KSP ksp,PetscBool flag)
    291: {
    294:   ksp->skippcsetfromoptions = flag;
    295:   return(0);
    296: }

    298: /*@
    299:    KSPSetUp - Sets up the internal data structures for the
    300:    later use of an iterative solver.

    302:    Collective on ksp

    304:    Input Parameter:
    305: .  ksp   - iterative context obtained from KSPCreate()

    307:    Level: developer

    309: .seealso: KSPCreate(), KSPSolve(), KSPDestroy(), KSP
    310: @*/
    311: PetscErrorCode KSPSetUp(KSP ksp)
    312: {
    314:   Mat            A,B;
    315:   Mat            mat,pmat;
    316:   MatNullSpace   nullsp;
    317:   PCFailedReason pcreason;

    322:   /* reset the convergence flag from the previous solves */
    323:   ksp->reason = KSP_CONVERGED_ITERATING;

    325:   if (!((PetscObject)ksp)->type_name) {
    326:     KSPSetType(ksp,KSPGMRES);
    327:   }
    328:   KSPSetUpNorms_Private(ksp,PETSC_TRUE,&ksp->normtype,&ksp->pc_side);

    330:   if (ksp->dmActive && !ksp->setupstage) {
    331:     /* first time in so build matrix and vector data structures using DM */
    332:     if (!ksp->vec_rhs) {DMCreateGlobalVector(ksp->dm,&ksp->vec_rhs);}
    333:     if (!ksp->vec_sol) {DMCreateGlobalVector(ksp->dm,&ksp->vec_sol);}
    334:     DMCreateMatrix(ksp->dm,&A);
    335:     KSPSetOperators(ksp,A,A);
    336:     PetscObjectDereference((PetscObject)A);
    337:   }

    339:   if (ksp->dmActive) {
    340:     DMKSP kdm;
    341:     DMGetDMKSP(ksp->dm,&kdm);

    343:     if (kdm->ops->computeinitialguess && ksp->setupstage != KSP_SETUP_NEWRHS) {
    344:       /* only computes initial guess the first time through */
    345:       (*kdm->ops->computeinitialguess)(ksp,ksp->vec_sol,kdm->initialguessctx);
    346:       KSPSetInitialGuessNonzero(ksp,PETSC_TRUE);
    347:     }
    348:     if (kdm->ops->computerhs) {
    349:       (*kdm->ops->computerhs)(ksp,ksp->vec_rhs,kdm->rhsctx);
    350:     }

    352:     if (ksp->setupstage != KSP_SETUP_NEWRHS) {
    353:       if (kdm->ops->computeoperators) {
    354:         KSPGetOperators(ksp,&A,&B);
    355:         (*kdm->ops->computeoperators)(ksp,A,B,kdm->operatorsctx);
    356:       } else SETERRQ(PetscObjectComm((PetscObject)ksp),PETSC_ERR_ARG_WRONGSTATE,"You called KSPSetDM() but did not use DMKSPSetComputeOperators() or KSPSetDMActive(ksp,PETSC_FALSE);");
    357:     }
    358:   }

    360:   if (ksp->setupstage == KSP_SETUP_NEWRHS) return(0);
    361:   PetscLogEventBegin(KSP_SetUp,ksp,ksp->vec_rhs,ksp->vec_sol,0);

    363:   switch (ksp->setupstage) {
    364:   case KSP_SETUP_NEW:
    365:     (*ksp->ops->setup)(ksp);
    366:     break;
    367:   case KSP_SETUP_NEWMATRIX: {   /* This should be replaced with a more general mechanism */
    368:     if (ksp->setupnewmatrix) {
    369:       (*ksp->ops->setup)(ksp);
    370:     }
    371:   } break;
    372:   default: break;
    373:   }

    375:   if (!ksp->pc) {KSPGetPC(ksp,&ksp->pc);}
    376:   PCGetOperators(ksp->pc,&mat,&pmat);
    377:   /* scale the matrix if requested */
    378:   if (ksp->dscale) {
    379:     PetscScalar *xx;
    380:     PetscInt    i,n;
    381:     PetscBool   zeroflag = PETSC_FALSE;
    382:     if (!ksp->pc) {KSPGetPC(ksp,&ksp->pc);}
    383:     if (!ksp->diagonal) { /* allocate vector to hold diagonal */
    384:       MatCreateVecs(pmat,&ksp->diagonal,NULL);
    385:     }
    386:     MatGetDiagonal(pmat,ksp->diagonal);
    387:     VecGetLocalSize(ksp->diagonal,&n);
    388:     VecGetArray(ksp->diagonal,&xx);
    389:     for (i=0; i<n; i++) {
    390:       if (xx[i] != 0.0) xx[i] = 1.0/PetscSqrtReal(PetscAbsScalar(xx[i]));
    391:       else {
    392:         xx[i]    = 1.0;
    393:         zeroflag = PETSC_TRUE;
    394:       }
    395:     }
    396:     VecRestoreArray(ksp->diagonal,&xx);
    397:     if (zeroflag) {
    398:       PetscInfo(ksp,"Zero detected in diagonal of matrix, using 1 at those locations\n");
    399:     }
    400:     MatDiagonalScale(pmat,ksp->diagonal,ksp->diagonal);
    401:     if (mat != pmat) {MatDiagonalScale(mat,ksp->diagonal,ksp->diagonal);}
    402:     ksp->dscalefix2 = PETSC_FALSE;
    403:   }
    404:   PetscLogEventEnd(KSP_SetUp,ksp,ksp->vec_rhs,ksp->vec_sol,0);
    405:   PCSetErrorIfFailure(ksp->pc,ksp->errorifnotconverged);
    406:   PCSetUp(ksp->pc);
    407:   PCGetFailedReasonRank(ksp->pc,&pcreason);
    408:   /* TODO: this code was wrong and is still wrong, there is no way to propogate the failure to all processes; their is no code to handle a ksp->reason on only some ranks */
    409:   if (pcreason) {
    410:     ksp->reason = KSP_DIVERGED_PC_FAILED;
    411:   }

    413:   MatGetNullSpace(mat,&nullsp);
    414:   if (nullsp) {
    415:     PetscBool test = PETSC_FALSE;
    416:     PetscOptionsGetBool(((PetscObject)ksp)->options,((PetscObject)ksp)->prefix,"-ksp_test_null_space",&test,NULL);
    417:     if (test) {
    418:       MatNullSpaceTest(nullsp,mat,NULL);
    419:     }
    420:   }
    421:   ksp->setupstage = KSP_SETUP_NEWRHS;
    422:   return(0);
    423: }

    425: /*@C
    426:    KSPConvergedReasonView - Displays the reason a KSP solve converged or diverged to a viewer

    428:    Collective on ksp

    430:    Parameter:
    431: +  ksp - iterative context obtained from KSPCreate()
    432: -  viewer - the viewer to display the reason

    434:    Options Database Keys:
    435: +  -ksp_converged_reason - print reason for converged or diverged, also prints number of iterations
    436: -  -ksp_converged_reason ::failed - only print reason and number of iterations when diverged

    438:    Notes:
    439:      To change the format of the output call PetscViewerPushFormat(viewer,format) before this call. Use PETSC_VIEWER_DEFAULT for the default,
    440:      use PETSC_VIEWER_FAILED to only display a reason if it fails.

    442:    Level: beginner

    444: .seealso: KSPCreate(), KSPSetUp(), KSPDestroy(), KSPSetTolerances(), KSPConvergedDefault(),
    445:           KSPSolveTranspose(), KSPGetIterationNumber(), KSP, KSPGetConvergedReason(), PetscViewerPushFormat(), PetscViewerPopFormat()
    446: @*/
    447: PetscErrorCode KSPConvergedReasonView(KSP ksp, PetscViewer viewer)
    448: {
    449:   PetscErrorCode    ierr;
    450:   PetscBool         isAscii;
    451:   PetscViewerFormat format;

    454:   if (!viewer) viewer = PETSC_VIEWER_STDOUT_(PetscObjectComm((PetscObject)ksp));
    455:   PetscObjectTypeCompare((PetscObject)viewer,PETSCVIEWERASCII,&isAscii);
    456:   if (isAscii) {
    457:     PetscViewerGetFormat(viewer, &format);
    458:     PetscViewerASCIIAddTab(viewer,((PetscObject)ksp)->tablevel);
    459:     if (ksp->reason > 0 && format != PETSC_VIEWER_FAILED) {
    460:       if (((PetscObject) ksp)->prefix) {
    461:         PetscViewerASCIIPrintf(viewer,"Linear %s solve converged due to %s iterations %D\n",((PetscObject) ksp)->prefix,KSPConvergedReasons[ksp->reason],ksp->its);
    462:       } else {
    463:         PetscViewerASCIIPrintf(viewer,"Linear solve converged due to %s iterations %D\n",KSPConvergedReasons[ksp->reason],ksp->its);
    464:       }
    465:     } else if (ksp->reason <= 0) {
    466:       if (((PetscObject) ksp)->prefix) {
    467:         PetscViewerASCIIPrintf(viewer,"Linear %s solve did not converge due to %s iterations %D\n",((PetscObject) ksp)->prefix,KSPConvergedReasons[ksp->reason],ksp->its);
    468:       } else {
    469:         PetscViewerASCIIPrintf(viewer,"Linear solve did not converge due to %s iterations %D\n",KSPConvergedReasons[ksp->reason],ksp->its);
    470:       }
    471:       if (ksp->reason == KSP_DIVERGED_PC_FAILED) {
    472:         PCFailedReason reason;
    473:         PCGetFailedReason(ksp->pc,&reason);
    474:         PetscViewerASCIIPrintf(viewer,"               PC failed due to %s \n",PCFailedReasons[reason]);
    475:       }
    476:     }
    477:     PetscViewerASCIISubtractTab(viewer,((PetscObject)ksp)->tablevel);
    478:   }
    479:   return(0);
    480: }

    482: /*@C
    483:    KSPConvergedReasonViewSet - Sets an ADDITIONAL function that is to be used at the
    484:     end of the linear solver to display the convergence reason of the linear solver.

    486:    Logically Collective on KSP

    488:    Input Parameters:
    489: +  ksp - the KSP context
    490: .  f - the ksp converged reason view function
    491: .  vctx - [optional] user-defined context for private data for the
    492:           ksp converged reason view routine (use NULL if no context is desired)
    493: -  reasonviewdestroy - [optional] routine that frees reasonview context
    494:           (may be NULL)

    496:    Options Database Keys:
    497: +    -ksp_converged_reason        - sets a default KSPConvergedReasonView()
    498: -    -ksp_converged_reason_view_cancel - cancels all converged reason viewers that have
    499:                             been hardwired into a code by
    500:                             calls to KSPConvergedReasonViewSet(), but
    501:                             does not cancel those set via
    502:                             the options database.

    504:    Notes:
    505:    Several different converged reason view routines may be set by calling
    506:    KSPConvergedReasonViewSet() multiple times; all will be called in the
    507:    order in which they were set.

    509:    Level: intermediate

    511: .seealso: KSPConvergedReasonView(), KSPConvergedReasonViewCancel()
    512: @*/
    513: PetscErrorCode  KSPConvergedReasonViewSet(KSP ksp,PetscErrorCode (*f)(KSP,void*),void *vctx,PetscErrorCode (*reasonviewdestroy)(void**))
    514: {
    515:   PetscInt       i;
    517:   PetscBool      identical;

    521:   for (i=0; i<ksp->numberreasonviews;i++) {
    522:     PetscMonitorCompare((PetscErrorCode (*)(void))f,vctx,reasonviewdestroy,(PetscErrorCode (*)(void))ksp->reasonview[i],ksp->reasonviewcontext[i],ksp->reasonviewdestroy[i],&identical);
    523:     if (identical) return(0);
    524:   }
    525:   if (ksp->numberreasonviews >= MAXKSPREASONVIEWS) SETERRQ(PETSC_COMM_SELF,PETSC_ERR_ARG_OUTOFRANGE,"Too many KSP reasonview set");
    526:   ksp->reasonview[ksp->numberreasonviews]          = f;
    527:   ksp->reasonviewdestroy[ksp->numberreasonviews]   = reasonviewdestroy;
    528:   ksp->reasonviewcontext[ksp->numberreasonviews++] = (void*)vctx;
    529:   return(0);
    530: }

    532: /*@
    533:    KSPConvergedReasonViewCancel - Clears all the reasonview functions for a KSP object.

    535:    Collective on KSP

    537:    Input Parameter:
    538: .  ksp - iterative context obtained from KSPCreate()

    540:    Level: intermediate

    542: .seealso: KSPCreate(), KSPDestroy(), KSPReset()
    543: @*/
    544: PetscErrorCode  KSPConvergedReasonViewCancel(KSP ksp)
    545: {
    547:   PetscInt       i;

    551:   for (i=0; i<ksp->numberreasonviews; i++) {
    552:     if (ksp->reasonviewdestroy[i]) {
    553:       (*ksp->reasonviewdestroy[i])(&ksp->reasonviewcontext[i]);
    554:     }
    555:   }
    556:   ksp->numberreasonviews = 0;
    557:   return(0);
    558: }

    560: /*@
    561:   KSPConvergedReasonViewFromOptions - Processes command line options to determine if/how a KSPReason is to be viewed.

    563:   Collective on ksp

    565:   Input Parameters:
    566: . ksp   - the KSP object

    568:   Level: intermediate

    570: .seealso: KSPConvergedReasonView()
    571: @*/
    572: PetscErrorCode KSPConvergedReasonViewFromOptions(KSP ksp)
    573: {
    574:   PetscViewer       viewer;
    575:   PetscBool         flg;
    576:   PetscViewerFormat format;
    577:   PetscErrorCode    ierr;
    578:   PetscInt          i;

    582:   /* Call all user-provided reason review routines */
    583:   for (i=0; i<ksp->numberreasonviews; i++) {
    584:     (*ksp->reasonview[i])(ksp,ksp->reasonviewcontext[i]);
    585:   }

    587:   /* Call the default PETSc routine */
    588:   PetscOptionsGetViewer(PetscObjectComm((PetscObject)ksp),((PetscObject)ksp)->options,((PetscObject)ksp)->prefix,"-ksp_converged_reason",&viewer,&format,&flg);
    589:   if (flg) {
    590:     PetscViewerPushFormat(viewer,format);
    591:     KSPConvergedReasonView(ksp, viewer);
    592:     PetscViewerPopFormat(viewer);
    593:     PetscViewerDestroy(&viewer);
    594:   }
    595:   return(0);
    596: }

    598: /*@C
    599:   KSPConvergedRateView - Displays the reason a KSP solve converged or diverged to a viewer

    601:   Collective on ksp

    603:   Input Parameters:
    604: +  ksp    - iterative context obtained from KSPCreate()
    605: -  viewer - the viewer to display the reason

    607:   Options Database Keys:
    608: . -ksp_converged_rate - print reason for convergence or divergence and the convergence rate (or 0.0 for divergence)

    610:   Notes:
    611:   To change the format of the output, call PetscViewerPushFormat(viewer,format) before this call.

    613:   Suppose that the residual is reduced linearly, $r_k = c^k r_0$, which means $log r_k = log r_0 + k log c$. After linear regression,
    614:   the slope is $\log c$. The coefficient of determination is given by $1 - \frac{\sum_i (y_i - f(x_i))^2}{\sum_i (y_i - \bar y)}$,
    615:   see also https://en.wikipedia.org/wiki/Coefficient_of_determination

    617:   Level: intermediate

    619: .seealso: KSPConvergedReasonView(), KSPGetConvergedRate(), KSPSetTolerances(), KSPConvergedDefault()
    620: @*/
    621: PetscErrorCode KSPConvergedRateView(KSP ksp, PetscViewer viewer)
    622: {
    623:   PetscViewerFormat format;
    624:   PetscBool         isAscii;
    625:   PetscReal         rrate, rRsq, erate, eRsq;
    626:   PetscInt          its;
    627:   const char       *prefix, *reason = KSPConvergedReasons[ksp->reason];
    628:   PetscErrorCode    ierr;

    631:   KSPGetOptionsPrefix(ksp, &prefix);
    632:   KSPGetIterationNumber(ksp, &its);
    633:   KSPComputeConvergenceRate(ksp, &rrate, &rRsq, &erate, &eRsq);
    634:   if (!viewer) viewer = PETSC_VIEWER_STDOUT_(PetscObjectComm((PetscObject)ksp));
    635:   PetscObjectTypeCompare((PetscObject)viewer,PETSCVIEWERASCII,&isAscii);
    636:   if (isAscii) {
    637:     PetscViewerGetFormat(viewer, &format);
    638:     PetscViewerASCIIAddTab(viewer,((PetscObject)ksp)->tablevel);
    639:     if (ksp->reason > 0) {
    640:       if (prefix) {PetscViewerASCIIPrintf(viewer, "Linear %s solve converged due to %s iterations %D", prefix, reason, its);}
    641:       else        {PetscViewerASCIIPrintf(viewer, "Linear solve converged due to %s iterations %D", reason, its);}
    642:       PetscViewerASCIIUseTabs(viewer, PETSC_FALSE);
    643:       if (rRsq >= 0.0) {PetscViewerASCIIPrintf(viewer, " res rate %g R^2 %g", rrate, rRsq);}
    644:       if (eRsq >= 0.0) {PetscViewerASCIIPrintf(viewer, " error rate %g R^2 %g", erate, eRsq);}
    645:       PetscViewerASCIIPrintf(viewer, "\n");
    646:       PetscViewerASCIIUseTabs(viewer, PETSC_TRUE);
    647:     } else if (ksp->reason <= 0) {
    648:       if (prefix) {PetscViewerASCIIPrintf(viewer, "Linear %s solve did not converge due to %s iterations %D", prefix, reason, its);}
    649:       else        {PetscViewerASCIIPrintf(viewer, "Linear solve did not converge due to %s iterations %D", reason, its);}
    650:       PetscViewerASCIIUseTabs(viewer, PETSC_FALSE);
    651:       if (rRsq >= 0.0) {PetscViewerASCIIPrintf(viewer, " res rate %g R^2 %g", rrate, rRsq);}
    652:       if (eRsq >= 0.0) {PetscViewerASCIIPrintf(viewer, " error rate %g R^2 %g", erate, eRsq);}
    653:       PetscViewerASCIIPrintf(viewer, "\n");
    654:       PetscViewerASCIIUseTabs(viewer, PETSC_TRUE);
    655:       if (ksp->reason == KSP_DIVERGED_PC_FAILED) {
    656:         PCFailedReason reason;
    657:         PCGetFailedReason(ksp->pc,&reason);
    658:         PetscViewerASCIIPrintf(viewer,"               PC failed due to %s \n",PCFailedReasons[reason]);
    659:       }
    660:     }
    661:     PetscViewerASCIISubtractTab(viewer,((PetscObject)ksp)->tablevel);
    662:   }
    663:   return(0);
    664: }

    666: #include <petscdraw.h>

    668: static PetscErrorCode KSPViewEigenvalues_Internal(KSP ksp, PetscBool isExplicit, PetscViewer viewer, PetscViewerFormat format)
    669: {
    670:   PetscReal     *r, *c;
    671:   PetscInt       n, i, neig;
    672:   PetscBool      isascii, isdraw;
    673:   PetscMPIInt    rank;

    677:   MPI_Comm_rank(PetscObjectComm((PetscObject) ksp), &rank);
    678:   PetscObjectTypeCompare((PetscObject) viewer, PETSCVIEWERASCII, &isascii);
    679:   PetscObjectTypeCompare((PetscObject) viewer, PETSCVIEWERDRAW,  &isdraw);
    680:   if (isExplicit) {
    681:     VecGetSize(ksp->vec_sol,&n);
    682:     PetscMalloc2(n, &r, n, &c);
    683:     KSPComputeEigenvaluesExplicitly(ksp, n, r, c);
    684:     neig = n;
    685:   } else {
    686:     PetscInt nits;

    688:     KSPGetIterationNumber(ksp, &nits);
    689:     n    = nits+2;
    690:     if (!nits) {PetscViewerASCIIPrintf(viewer, "Zero iterations in solver, cannot approximate any eigenvalues\n");return(0);}
    691:     PetscMalloc2(n, &r, n, &c);
    692:     KSPComputeEigenvalues(ksp, n, r, c, &neig);
    693:   }
    694:   if (isascii) {
    695:     PetscViewerASCIIPrintf(viewer, "%s computed eigenvalues\n", isExplicit ? "Explicitly" : "Iteratively");
    696:     for (i = 0; i < neig; ++i) {
    697:       if (c[i] >= 0.0) {PetscViewerASCIIPrintf(viewer, "%g + %gi\n", (double) r[i],  (double) c[i]);}
    698:       else             {PetscViewerASCIIPrintf(viewer, "%g - %gi\n", (double) r[i], -(double) c[i]);}
    699:     }
    700:   } else if (isdraw && !rank) {
    701:     PetscDraw   draw;
    702:     PetscDrawSP drawsp;

    704:     if (format == PETSC_VIEWER_DRAW_CONTOUR) {
    705:       KSPPlotEigenContours_Private(ksp,neig,r,c);
    706:     } else {
    707:       if (!ksp->eigviewer) {PetscViewerDrawOpen(PETSC_COMM_SELF,NULL,isExplicit ? "Explicitly Computed Eigenvalues" : "Iteratively Computed Eigenvalues",PETSC_DECIDE,PETSC_DECIDE,400,400,&ksp->eigviewer);}
    708:       PetscViewerDrawGetDraw(ksp->eigviewer,0,&draw);
    709:       PetscDrawSPCreate(draw,1,&drawsp);
    710:       PetscDrawSPReset(drawsp);
    711:       for (i = 0; i < neig; ++i) {PetscDrawSPAddPoint(drawsp,r+i,c+i);}
    712:       PetscDrawSPDraw(drawsp,PETSC_TRUE);
    713:       PetscDrawSPSave(drawsp);
    714:       PetscDrawSPDestroy(&drawsp);
    715:     }
    716:   }
    717:   PetscFree2(r, c);
    718:   return(0);
    719: }

    721: static PetscErrorCode KSPViewSingularvalues_Internal(KSP ksp, PetscViewer viewer, PetscViewerFormat format)
    722: {
    723:   PetscReal      smax, smin;
    724:   PetscInt       nits;
    725:   PetscBool      isascii;

    729:   PetscObjectTypeCompare((PetscObject) viewer, PETSCVIEWERASCII, &isascii);
    730:   KSPGetIterationNumber(ksp, &nits);
    731:   if (!nits) {PetscViewerASCIIPrintf(viewer, "Zero iterations in solver, cannot approximate any singular values\n");return(0);}
    732:   KSPComputeExtremeSingularValues(ksp, &smax, &smin);
    733:   if (isascii) {PetscViewerASCIIPrintf(viewer, "Iteratively computed extreme singular values: max %g min %g max/min %g\n",(double)smax,(double)smin,(double)(smax/smin));}
    734:   return(0);
    735: }

    737: static PetscErrorCode KSPViewFinalResidual_Internal(KSP ksp, PetscViewer viewer, PetscViewerFormat format)
    738: {
    739:   PetscBool      isascii;

    743:   PetscObjectTypeCompare((PetscObject) viewer, PETSCVIEWERASCII, &isascii);
    744:   if (ksp->dscale && !ksp->dscalefix) SETERRQ(PetscObjectComm((PetscObject) ksp), PETSC_ERR_ARG_WRONGSTATE, "Cannot compute final scale with -ksp_diagonal_scale except also with -ksp_diagonal_scale_fix");
    745:   if (isascii) {
    746:     Mat       A;
    747:     Vec       t;
    748:     PetscReal norm;

    750:     PCGetOperators(ksp->pc, &A, NULL);
    751:     VecDuplicate(ksp->vec_rhs, &t);
    752:     KSP_MatMult(ksp, A, ksp->vec_sol, t);
    753:     VecAYPX(t, -1.0, ksp->vec_rhs);
    754:     VecNorm(t, NORM_2, &norm);
    755:     VecDestroy(&t);
    756:     PetscViewerASCIIPrintf(viewer, "KSP final norm of residual %g\n", (double) norm);
    757:   }
    758:   return(0);
    759: }

    761: static PetscErrorCode KSPMonitorPauseFinal_Internal(KSP ksp)
    762: {
    763:   PetscInt       i;

    767:   if (!ksp->pauseFinal) return(0);
    768:   for (i = 0; i < ksp->numbermonitors; ++i) {
    769:     PetscViewerAndFormat *vf = (PetscViewerAndFormat *) ksp->monitorcontext[i];
    770:     PetscDraw             draw;
    771:     PetscReal             lpause;

    773:     if (!vf) continue;
    774:     if (vf->lg) {
    776:       if (((PetscObject) vf->lg)->classid != PETSC_DRAWLG_CLASSID) continue;
    777:       PetscDrawLGGetDraw(vf->lg, &draw);
    778:       PetscDrawGetPause(draw, &lpause);
    779:       PetscDrawSetPause(draw, -1.0);
    780:       PetscDrawPause(draw);
    781:       PetscDrawSetPause(draw, lpause);
    782:     } else {
    783:       PetscBool isdraw;

    786:       if (((PetscObject) vf->viewer)->classid != PETSC_VIEWER_CLASSID) continue;
    787:       PetscObjectTypeCompare((PetscObject) vf->viewer, PETSCVIEWERDRAW, &isdraw);
    788:       if (!isdraw) continue;
    789:       PetscViewerDrawGetDraw(vf->viewer, 0, &draw);
    790:       PetscDrawGetPause(draw, &lpause);
    791:       PetscDrawSetPause(draw, -1.0);
    792:       PetscDrawPause(draw);
    793:       PetscDrawSetPause(draw, lpause);
    794:     }
    795:   }
    796:   return(0);
    797: }

    799: static PetscErrorCode KSPSolve_Private(KSP ksp,Vec b,Vec x)
    800: {
    802:   PetscBool      flg = PETSC_FALSE,inXisinB=PETSC_FALSE,guess_zero;
    803:   Mat            mat,pmat;
    804:   MPI_Comm       comm;
    805:   MatNullSpace   nullsp;
    806:   Vec            btmp,vec_rhs=NULL;

    809:   comm = PetscObjectComm((PetscObject)ksp);
    810:   if (x && x == b) {
    811:     if (!ksp->guess_zero) SETERRQ(comm,PETSC_ERR_ARG_INCOMP,"Cannot use x == b with nonzero initial guess");
    812:     VecDuplicate(b,&x);
    813:     inXisinB = PETSC_TRUE;
    814:   }
    815:   if (b) {
    816:     PetscObjectReference((PetscObject)b);
    817:     VecDestroy(&ksp->vec_rhs);
    818:     ksp->vec_rhs = b;
    819:   }
    820:   if (x) {
    821:     PetscObjectReference((PetscObject)x);
    822:     VecDestroy(&ksp->vec_sol);
    823:     ksp->vec_sol = x;
    824:   }

    826:   if (ksp->viewPre) {ObjectView((PetscObject) ksp, ksp->viewerPre, ksp->formatPre);}

    828:   if (ksp->presolve) {(*ksp->presolve)(ksp,ksp->vec_rhs,ksp->vec_sol,ksp->prectx);}

    830:   /* reset the residual history list if requested */
    831:   if (ksp->res_hist_reset) ksp->res_hist_len = 0;
    832:   if (ksp->err_hist_reset) ksp->err_hist_len = 0;

    834:   if (ksp->guess) {
    835:     PetscObjectState ostate,state;

    837:     KSPGuessSetUp(ksp->guess);
    838:     PetscObjectStateGet((PetscObject)ksp->vec_sol,&ostate);
    839:     KSPGuessFormGuess(ksp->guess,ksp->vec_rhs,ksp->vec_sol);
    840:     PetscObjectStateGet((PetscObject)ksp->vec_sol,&state);
    841:     if (state != ostate) {
    842:       ksp->guess_zero = PETSC_FALSE;
    843:     } else {
    844:       PetscInfo(ksp,"Using zero initial guess since the KSPGuess object did not change the vector\n");
    845:       ksp->guess_zero = PETSC_TRUE;
    846:     }
    847:   }

    849:   /* KSPSetUp() scales the matrix if needed */
    850:   KSPSetUp(ksp);
    851:   KSPSetUpOnBlocks(ksp);

    853:   VecSetErrorIfLocked(ksp->vec_sol,3);

    855:   PetscLogEventBegin(KSP_Solve,ksp,ksp->vec_rhs,ksp->vec_sol,0);
    856:   PCGetOperators(ksp->pc,&mat,&pmat);
    857:   /* diagonal scale RHS if called for */
    858:   if (ksp->dscale) {
    859:     VecPointwiseMult(ksp->vec_rhs,ksp->vec_rhs,ksp->diagonal);
    860:     /* second time in, but matrix was scaled back to original */
    861:     if (ksp->dscalefix && ksp->dscalefix2) {
    862:       Mat mat,pmat;

    864:       PCGetOperators(ksp->pc,&mat,&pmat);
    865:       MatDiagonalScale(pmat,ksp->diagonal,ksp->diagonal);
    866:       if (mat != pmat) {MatDiagonalScale(mat,ksp->diagonal,ksp->diagonal);}
    867:     }

    869:     /* scale initial guess */
    870:     if (!ksp->guess_zero) {
    871:       if (!ksp->truediagonal) {
    872:         VecDuplicate(ksp->diagonal,&ksp->truediagonal);
    873:         VecCopy(ksp->diagonal,ksp->truediagonal);
    874:         VecReciprocal(ksp->truediagonal);
    875:       }
    876:       VecPointwiseMult(ksp->vec_sol,ksp->vec_sol,ksp->truediagonal);
    877:     }
    878:   }
    879:   PCPreSolve(ksp->pc,ksp);

    881:   if (ksp->guess_zero) { VecSet(ksp->vec_sol,0.0);}
    882:   if (ksp->guess_knoll) { /* The Knoll trick is independent on the KSPGuess specified */
    883:     PCApply(ksp->pc,ksp->vec_rhs,ksp->vec_sol);
    884:     KSP_RemoveNullSpace(ksp,ksp->vec_sol);
    885:     ksp->guess_zero = PETSC_FALSE;
    886:   }

    888:   /* can we mark the initial guess as zero for this solve? */
    889:   guess_zero = ksp->guess_zero;
    890:   if (!ksp->guess_zero) {
    891:     PetscReal norm;

    893:     VecNormAvailable(ksp->vec_sol,NORM_2,&flg,&norm);
    894:     if (flg && !norm) ksp->guess_zero = PETSC_TRUE;
    895:   }
    896:   if (ksp->transpose_solve) {
    897:     MatGetNullSpace(pmat,&nullsp);
    898:   } else {
    899:     MatGetTransposeNullSpace(pmat,&nullsp);
    900:   }
    901:   if (nullsp) {
    902:     VecDuplicate(ksp->vec_rhs,&btmp);
    903:     VecCopy(ksp->vec_rhs,btmp);
    904:     MatNullSpaceRemove(nullsp,btmp);
    905:     vec_rhs      = ksp->vec_rhs;
    906:     ksp->vec_rhs = btmp;
    907:   }
    908:   VecLockReadPush(ksp->vec_rhs);
    909:   if (ksp->reason == KSP_DIVERGED_PC_FAILED) {
    910:     VecSetInf(ksp->vec_sol);
    911:   }
    912:   (*ksp->ops->solve)(ksp);
    913:   KSPMonitorPauseFinal_Internal(ksp);

    915:   VecLockReadPop(ksp->vec_rhs);
    916:   if (nullsp) {
    917:     ksp->vec_rhs = vec_rhs;
    918:     VecDestroy(&btmp);
    919:   }

    921:   ksp->guess_zero = guess_zero;

    923:   if (!ksp->reason) SETERRQ(comm,PETSC_ERR_PLIB,"Internal error, solver returned without setting converged reason");
    924:   ksp->totalits += ksp->its;

    926:   KSPConvergedReasonViewFromOptions(ksp);

    928:   if (ksp->viewRate) {
    929:     PetscViewerPushFormat(ksp->viewerRate,ksp->formatRate);
    930:     KSPConvergedRateView(ksp, ksp->viewerRate);
    931:     PetscViewerPopFormat(ksp->viewerRate);
    932:   }
    933:   PCPostSolve(ksp->pc,ksp);

    935:   /* diagonal scale solution if called for */
    936:   if (ksp->dscale) {
    937:     VecPointwiseMult(ksp->vec_sol,ksp->vec_sol,ksp->diagonal);
    938:     /* unscale right hand side and matrix */
    939:     if (ksp->dscalefix) {
    940:       Mat mat,pmat;

    942:       VecReciprocal(ksp->diagonal);
    943:       VecPointwiseMult(ksp->vec_rhs,ksp->vec_rhs,ksp->diagonal);
    944:       PCGetOperators(ksp->pc,&mat,&pmat);
    945:       MatDiagonalScale(pmat,ksp->diagonal,ksp->diagonal);
    946:       if (mat != pmat) {MatDiagonalScale(mat,ksp->diagonal,ksp->diagonal);}
    947:       VecReciprocal(ksp->diagonal);
    948:       ksp->dscalefix2 = PETSC_TRUE;
    949:     }
    950:   }
    951:   PetscLogEventEnd(KSP_Solve,ksp,ksp->vec_rhs,ksp->vec_sol,0);
    952:   if (ksp->guess) {
    953:     KSPGuessUpdate(ksp->guess,ksp->vec_rhs,ksp->vec_sol);
    954:   }
    955:   if (ksp->postsolve) {
    956:     (*ksp->postsolve)(ksp,ksp->vec_rhs,ksp->vec_sol,ksp->postctx);
    957:   }

    959:   PCGetOperators(ksp->pc,&mat,&pmat);
    960:   if (ksp->viewEV)       {KSPViewEigenvalues_Internal(ksp, PETSC_FALSE, ksp->viewerEV,    ksp->formatEV);}
    961:   if (ksp->viewEVExp)    {KSPViewEigenvalues_Internal(ksp, PETSC_TRUE,  ksp->viewerEVExp, ksp->formatEVExp);}
    962:   if (ksp->viewSV)       {KSPViewSingularvalues_Internal(ksp, ksp->viewerSV, ksp->formatSV);}
    963:   if (ksp->viewFinalRes) {KSPViewFinalResidual_Internal(ksp, ksp->viewerFinalRes, ksp->formatFinalRes);}
    964:   if (ksp->viewMat)      {ObjectView((PetscObject) mat,           ksp->viewerMat,    ksp->formatMat);}
    965:   if (ksp->viewPMat)     {ObjectView((PetscObject) pmat,          ksp->viewerPMat,   ksp->formatPMat);}
    966:   if (ksp->viewRhs)      {ObjectView((PetscObject) ksp->vec_rhs,  ksp->viewerRhs,    ksp->formatRhs);}
    967:   if (ksp->viewSol)      {ObjectView((PetscObject) ksp->vec_sol,  ksp->viewerSol,    ksp->formatSol);}
    968:   if (ksp->view)         {ObjectView((PetscObject) ksp,           ksp->viewer,       ksp->format);}
    969:   if (ksp->viewDScale)   {ObjectView((PetscObject) ksp->diagonal, ksp->viewerDScale, ksp->formatDScale);}
    970:   if (ksp->viewMatExp)   {
    971:     Mat A, B;

    973:     PCGetOperators(ksp->pc, &A, NULL);
    974:     if (ksp->transpose_solve) {
    975:       Mat AT;

    977:       MatCreateTranspose(A, &AT);
    978:       MatComputeOperator(AT, MATAIJ, &B);
    979:       MatDestroy(&AT);
    980:     } else {
    981:       MatComputeOperator(A, MATAIJ, &B);
    982:     }
    983:     ObjectView((PetscObject) B, ksp->viewerMatExp, ksp->formatMatExp);
    984:     MatDestroy(&B);
    985:   }
    986:   if (ksp->viewPOpExp)   {
    987:     Mat B;

    989:     KSPComputeOperator(ksp, MATAIJ, &B);
    990:     ObjectView((PetscObject) B, ksp->viewerPOpExp, ksp->formatPOpExp);
    991:     MatDestroy(&B);
    992:   }

    994:   if (inXisinB) {
    995:     VecCopy(x,b);
    996:     VecDestroy(&x);
    997:   }
    998:   PetscObjectSAWsBlock((PetscObject)ksp);
    999:   if (ksp->errorifnotconverged && ksp->reason < 0 && ksp->reason != KSP_DIVERGED_ITS) {
    1000:     if (ksp->reason == KSP_DIVERGED_PC_FAILED) {
    1001:       PCFailedReason reason;
    1002:       PCGetFailedReason(ksp->pc,&reason);
    1003:       SETERRQ2(comm,PETSC_ERR_NOT_CONVERGED,"KSPSolve has not converged, reason %s PC failed due to %s",KSPConvergedReasons[ksp->reason],PCFailedReasons[reason]);
    1004:     } else SETERRQ1(comm,PETSC_ERR_NOT_CONVERGED,"KSPSolve has not converged, reason %s",KSPConvergedReasons[ksp->reason]);
    1005:   }
    1006:   return(0);
    1007: }

    1009: /*@
    1010:    KSPSolve - Solves linear system.

    1012:    Collective on ksp

    1014:    Parameters:
    1015: +  ksp - iterative context obtained from KSPCreate()
    1016: .  b - the right hand side vector
    1017: -  x - the solution (this may be the same vector as b, then b will be overwritten with answer)

    1019:    Options Database Keys:
    1020: +  -ksp_view_eigenvalues - compute preconditioned operators eigenvalues
    1021: .  -ksp_view_eigenvalues_explicit - compute the eigenvalues by forming the dense operator and using LAPACK
    1022: .  -ksp_view_mat binary - save matrix to the default binary viewer
    1023: .  -ksp_view_pmat binary - save matrix used to build preconditioner to the default binary viewer
    1024: .  -ksp_view_rhs binary - save right hand side vector to the default binary viewer
    1025: .  -ksp_view_solution binary - save computed solution vector to the default binary viewer
    1026:            (can be read later with src/ksp/tutorials/ex10.c for testing solvers)
    1027: .  -ksp_view_mat_explicit - for matrix-free operators, computes the matrix entries and views them
    1028: .  -ksp_view_preconditioned_operator_explicit - computes the product of the preconditioner and matrix as an explicit matrix and views it
    1029: .  -ksp_converged_reason - print reason for converged or diverged, also prints number of iterations
    1030: .  -ksp_view_final_residual - print 2-norm of true linear system residual at the end of the solution process
    1031: -  -ksp_view - print the ksp data structure at the end of the system solution

    1033:    Notes:

    1035:    If one uses KSPSetDM() then x or b need not be passed. Use KSPGetSolution() to access the solution in this case.

    1037:    The operator is specified with KSPSetOperators().

    1039:    Call KSPGetConvergedReason() to determine if the solver converged or failed and
    1040:    why. The number of iterations can be obtained from KSPGetIterationNumber().

    1042:    If you provide a matrix that has a MatSetNullSpace() and MatSetTransposeNullSpace() this will use that information to solve singular systems
    1043:    in the least squares sense with a norm minimizing solution.
    1044: $
    1045: $                   A x = b   where b = b_p + b_t where b_t is not in the range of A (and hence by the fundamental theorem of linear algebra is in the nullspace(A') see MatSetNullSpace()
    1046: $
    1047: $    KSP first removes b_t producing the linear system  A x = b_p (which has multiple solutions) and solves this to find the ||x|| minimizing solution (and hence
    1048: $    it finds the solution x orthogonal to the nullspace(A). The algorithm is simply in each iteration of the Krylov method we remove the nullspace(A) from the search
    1049: $    direction thus the solution which is a linear combination of the search directions has no component in the nullspace(A).
    1050: $
    1051: $    We recommend always using GMRES for such singular systems.
    1052: $    If nullspace(A) = nullspace(A') (note symmetric matrices always satisfy this property) then both left and right preconditioning will work
    1053: $    If nullspace(A) != nullspace(A') then left preconditioning will work but right preconditioning may not work (or it may).

    1055:    Developer Note: The reason we cannot always solve  nullspace(A) != nullspace(A') systems with right preconditioning is because we need to remove at each iteration
    1056:        the nullspace(AB) from the search direction. While we know the nullspace(A) the nullspace(AB) equals B^-1 times the nullspace(A) but except for trivial preconditioners
    1057:        such as diagonal scaling we cannot apply the inverse of the preconditioner to a vector and thus cannot compute the nullspace(AB).

    1060:    If using a direct method (e.g., via the KSP solver
    1061:    KSPPREONLY and a preconditioner such as PCLU/PCILU),
    1062:    then its=1.  See KSPSetTolerances() and KSPConvergedDefault()
    1063:    for more details.

    1065:    Understanding Convergence:
    1066:    The routines KSPMonitorSet(), KSPComputeEigenvalues(), and
    1067:    KSPComputeEigenvaluesExplicitly() provide information on additional
    1068:    options to monitor convergence and print eigenvalue information.

    1070:    Level: beginner

    1072: .seealso: KSPCreate(), KSPSetUp(), KSPDestroy(), KSPSetTolerances(), KSPConvergedDefault(),
    1073:           KSPSolveTranspose(), KSPGetIterationNumber(), MatNullSpaceCreate(), MatSetNullSpace(), MatSetTransposeNullSpace(), KSP,
    1074:           KSPConvergedReasonView()
    1075: @*/
    1076: PetscErrorCode KSPSolve(KSP ksp,Vec b,Vec x)
    1077: {

    1084:   ksp->transpose_solve = PETSC_FALSE;
    1085:   KSPSolve_Private(ksp,b,x);
    1086:   return(0);
    1087: }

    1089: /*@
    1090:    KSPSolveTranspose - Solves the transpose of a linear system.

    1092:    Collective on ksp

    1094:    Input Parameters:
    1095: +  ksp - iterative context obtained from KSPCreate()
    1096: .  b - right hand side vector
    1097: -  x - solution vector

    1099:    Notes:
    1100:     For complex numbers this solve the non-Hermitian transpose system.

    1102:    Developer Notes:
    1103:     We need to implement a KSPSolveHermitianTranspose()

    1105:    Level: developer

    1107: .seealso: KSPCreate(), KSPSetUp(), KSPDestroy(), KSPSetTolerances(), KSPConvergedDefault(),
    1108:           KSPSolve(), KSP
    1109: @*/
    1110: PetscErrorCode KSPSolveTranspose(KSP ksp,Vec b,Vec x)
    1111: {

    1118:   if (ksp->transpose.use_explicittranspose) {
    1119:     Mat J,Jpre;
    1120:     KSPGetOperators(ksp,&J,&Jpre);
    1121:     if (!ksp->transpose.reuse_transpose) {
    1122:       MatTranspose(J,MAT_INITIAL_MATRIX,&ksp->transpose.AT);
    1123:       if (J != Jpre) {
    1124:         MatTranspose(Jpre,MAT_INITIAL_MATRIX,&ksp->transpose.BT);
    1125:       }
    1126:       ksp->transpose.reuse_transpose = PETSC_TRUE;
    1127:     } else {
    1128:       MatTranspose(J,MAT_REUSE_MATRIX,&ksp->transpose.AT);
    1129:       if (J != Jpre) {
    1130:         MatTranspose(Jpre,MAT_REUSE_MATRIX,&ksp->transpose.BT);
    1131:       }
    1132:     }
    1133:     if (J == Jpre && ksp->transpose.BT != ksp->transpose.AT) {
    1134:       PetscObjectReference((PetscObject)ksp->transpose.AT);
    1135:       ksp->transpose.BT = ksp->transpose.AT;
    1136:     }
    1137:     KSPSetOperators(ksp,ksp->transpose.AT,ksp->transpose.BT);
    1138:   } else {
    1139:     ksp->transpose_solve = PETSC_TRUE;
    1140:   }
    1141:   KSPSolve_Private(ksp,b,x);
    1142:   return(0);
    1143: }

    1145: static PetscErrorCode KSPViewFinalMatResidual_Internal(KSP ksp, Mat B, Mat X, PetscViewer viewer, PetscViewerFormat format, PetscInt shift)
    1146: {
    1147:   Mat            A, R;
    1148:   PetscReal      *norms;
    1149:   PetscInt       i, N;
    1150:   PetscBool      flg;

    1154:   PetscObjectTypeCompare((PetscObject)viewer, PETSCVIEWERASCII, &flg);
    1155:   if (flg) {
    1156:     PCGetOperators(ksp->pc, &A, NULL);
    1157:     MatMatMult(A, X, MAT_INITIAL_MATRIX, PETSC_DEFAULT, &R);
    1158:     MatAYPX(R, -1.0, B, SAME_NONZERO_PATTERN);
    1159:     MatGetSize(R, NULL, &N);
    1160:     PetscMalloc1(N, &norms);
    1161:     MatGetColumnNorms(R, NORM_2, norms);
    1162:     MatDestroy(&R);
    1163:     for (i = 0; i < N; ++i) {
    1164:       PetscViewerASCIIPrintf(viewer, "%s #%D %g\n", i == 0 ? "KSP final norm of residual" : "                          ", shift + i, (double)norms[i]);
    1165:     }
    1166:     PetscFree(norms);
    1167:   }
    1168:   return(0);
    1169: }

    1171: /*@
    1172:      KSPMatSolve - Solves a linear system with multiple right-hand sides stored as a MATDENSE. Unlike KSPSolve(), B and X must be different matrices.

    1174:    Input Parameters:
    1175: +     ksp - iterative context
    1176: -     B - block of right-hand sides

    1178:    Output Parameter:
    1179: .     X - block of solutions

    1181:    Notes:
    1182:      This is a stripped-down version of KSPSolve(), which only handles -ksp_view, -ksp_converged_reason, and -ksp_view_final_residual.

    1184:    Level: intermediate

    1186: .seealso:  KSPSolve(), MatMatSolve(), MATDENSE, KSPHPDDM, PCBJACOBI, PCASM
    1187: @*/
    1188: PetscErrorCode KSPMatSolve(KSP ksp, Mat B, Mat X)
    1189: {
    1190:   Mat            A, vB, vX;
    1191:   Vec            cb, cx;
    1192:   PetscInt       m1, M1, m2, M2, n1, N1, n2, N2, Bbn = PETSC_DECIDE;
    1193:   PetscBool      match;

    1202:   if (!B->assembled) SETERRQ(PETSC_COMM_SELF, PETSC_ERR_ARG_WRONGSTATE, "Not for unassembled matrix");
    1203:   MatCheckPreallocated(X, 3);
    1204:   if (!X->assembled) {
    1205:     MatSetOption(X, MAT_NO_OFF_PROC_ENTRIES, PETSC_TRUE);
    1206:     MatAssemblyBegin(X, MAT_FINAL_ASSEMBLY);
    1207:     MatAssemblyEnd(X, MAT_FINAL_ASSEMBLY);
    1208:   }
    1209:   if (B == X) SETERRQ(PetscObjectComm((PetscObject)ksp), PETSC_ERR_ARG_IDN, "B and X must be different matrices");
    1210:   KSPGetOperators(ksp, &A, NULL);
    1211:   MatGetLocalSize(A, &m1, NULL);
    1212:   MatGetLocalSize(B, &m2, &n2);
    1213:   MatGetSize(A, &M1, NULL);
    1214:   MatGetSize(B, &M2, &N2);
    1215:   if (m1 != m2 || M1 != M2) SETERRQ4(PETSC_COMM_SELF, PETSC_ERR_ARG_SIZ, "Cannot use a block of right-hand sides with (m2,M2) = (%D,%D) for a linear system with (m1,M1) = (%D,%D)", m2, M2, m1, M1);
    1216:   MatGetLocalSize(X, &m1, &n1);
    1217:   MatGetSize(X, &M1, &N1);
    1218:   if (m1 != m2 || M1 != M2 || n1 != n2 || N1 != N2) SETERRQ8(PETSC_COMM_SELF, PETSC_ERR_ARG_SIZ, "Incompatible block of right-hand sides (m2,M2)x(n2,N2) = (%D,%D)x(%D,%D) and solutions (m1,M1)x(n1,N1) = (%D,%D)x(%D,%D)", m2, M2, n2, N2, m1, M1, n1, N1);
    1219:   PetscObjectBaseTypeCompareAny((PetscObject)B, &match, MATSEQDENSE, MATMPIDENSE, "");
    1220:   if (!match) SETERRQ(PETSC_COMM_SELF, PETSC_ERR_ARG_WRONG, "Provided block of right-hand sides not stored in a dense Mat");
    1221:   PetscObjectBaseTypeCompareAny((PetscObject)X, &match, MATSEQDENSE, MATMPIDENSE, "");
    1222:   if (!match) SETERRQ(PETSC_COMM_SELF, PETSC_ERR_ARG_WRONG, "Provided block of solutions not stored in a dense Mat");
    1223:   KSPSetUp(ksp);
    1224:   KSPSetUpOnBlocks(ksp);
    1225:   if (ksp->ops->matsolve) {
    1226:     if (ksp->guess_zero) {
    1227:       MatZeroEntries(X);
    1228:     }
    1229:     PetscLogEventBegin(KSP_MatSolve, ksp, B, X, 0);
    1230:     KSPGetMatSolveBatchSize(ksp, &Bbn);
    1231:     /* by default, do a single solve with all columns */
    1232:     if (Bbn == PETSC_DECIDE) Bbn = N2;
    1233:     else if (Bbn < 1) SETERRQ1(PetscObjectComm((PetscObject)ksp), PETSC_ERR_ARG_OUTOFRANGE, "KSPMatSolve() block size %D must be positive", Bbn);
    1234:     PetscInfo2(ksp, "KSP type %s solving using blocks of width at most %D\n", ((PetscObject)ksp)->type_name, Bbn);
    1235:     /* if -ksp_matsolve_batch_size is greater than the actual number of columns, do a single solve with all columns */
    1236:     if (Bbn >= N2) {
    1237:       (*ksp->ops->matsolve)(ksp, B, X);
    1238:       if (ksp->viewFinalRes) {
    1239:         KSPViewFinalMatResidual_Internal(ksp, B, X, ksp->viewerFinalRes, ksp->formatFinalRes, 0);
    1240:       }

    1242:       KSPConvergedReasonViewFromOptions(ksp);

    1244:       if (ksp->viewRate) {
    1245:         PetscViewerPushFormat(ksp->viewerRate,PETSC_VIEWER_DEFAULT);
    1246:         KSPConvergedRateView(ksp, ksp->viewerRate);
    1247:         PetscViewerPopFormat(ksp->viewerRate);
    1248:       }
    1249:     } else {
    1250:       for (n2 = 0; n2 < N2; n2 += Bbn) {
    1251:         MatDenseGetSubMatrix(B, n2, PetscMin(n2+Bbn, N2), &vB);
    1252:         MatDenseGetSubMatrix(X, n2, PetscMin(n2+Bbn, N2), &vX);
    1253:         (*ksp->ops->matsolve)(ksp, vB, vX);
    1254:         if (ksp->viewFinalRes) {
    1255:           KSPViewFinalMatResidual_Internal(ksp, vB, vX, ksp->viewerFinalRes, ksp->formatFinalRes, n2);
    1256:         }

    1258:         KSPConvergedReasonViewFromOptions(ksp);

    1260:         if (ksp->viewRate) {
    1261:           PetscViewerPushFormat(ksp->viewerRate,PETSC_VIEWER_DEFAULT);
    1262:           KSPConvergedRateView(ksp, ksp->viewerRate);
    1263:           PetscViewerPopFormat(ksp->viewerRate);
    1264:         }
    1265:         MatDenseRestoreSubMatrix(B, &vB);
    1266:         MatDenseRestoreSubMatrix(X, &vX);
    1267:       }
    1268:     }
    1269:     if (ksp->view) {
    1270:       KSPView(ksp, ksp->viewer);
    1271:     }
    1272:     PetscLogEventEnd(KSP_MatSolve, ksp, B, X, 0);
    1273:   } else {
    1274:     PetscInfo1(ksp, "KSP type %s solving column by column\n", ((PetscObject)ksp)->type_name);
    1275:     for (n2 = 0; n2 < N2; ++n2) {
    1276:       MatDenseGetColumnVecRead(B, n2, &cb);
    1277:       MatDenseGetColumnVecWrite(X, n2, &cx);
    1278:       KSPSolve(ksp, cb, cx);
    1279:       MatDenseRestoreColumnVecWrite(X, n2, &cx);
    1280:       MatDenseRestoreColumnVecRead(B, n2, &cb);
    1281:     }
    1282:   }
    1283:   return(0);
    1284: }

    1286: /*@
    1287:      KSPSetMatSolveBatchSize - Sets the maximum number of columns treated simultaneously in KSPMatSolve().

    1289:     Logically collective

    1291:    Input Parameters:
    1292: +     ksp - iterative context
    1293: -     bs - block size

    1295:    Level: advanced

    1297: .seealso:  KSPMatSolve(), KSPGetMatSolveBatchSize(), -mat_mumps_icntl_27, -matmatmult_Bbn
    1298: @*/
    1299: PetscErrorCode KSPSetMatSolveBatchSize(KSP ksp, PetscInt bs)
    1300: {
    1304:   ksp->nmax = bs;
    1305:   return(0);
    1306: }

    1308: /*@
    1309:      KSPGetMatSolveBatchSize - Gets the maximum number of columns treated simultaneously in KSPMatSolve().

    1311:    Input Parameter:
    1312: .     ksp - iterative context

    1314:    Output Parameter:
    1315: .     bs - block size

    1317:    Level: advanced

    1319: .seealso:  KSPMatSolve(), KSPSetMatSolveBatchSize(), -mat_mumps_icntl_27, -matmatmult_Bbn
    1320: @*/
    1321: PetscErrorCode KSPGetMatSolveBatchSize(KSP ksp, PetscInt *bs)
    1322: {
    1326:   *bs = ksp->nmax;
    1327:   return(0);
    1328: }

    1330: /*@
    1331:    KSPResetViewers - Resets all the viewers set from the options database during KSPSetFromOptions()

    1333:    Collective on ksp

    1335:    Input Parameter:
    1336: .  ksp - iterative context obtained from KSPCreate()

    1338:    Level: beginner

    1340: .seealso: KSPCreate(), KSPSetUp(), KSPSolve(), KSPSetFromOptions(), KSP
    1341: @*/
    1342: PetscErrorCode  KSPResetViewers(KSP ksp)
    1343: {

    1348:   if (!ksp) return(0);
    1349:   PetscViewerDestroy(&ksp->viewer);
    1350:   PetscViewerDestroy(&ksp->viewerPre);
    1351:   PetscViewerDestroy(&ksp->viewerRate);
    1352:   PetscViewerDestroy(&ksp->viewerMat);
    1353:   PetscViewerDestroy(&ksp->viewerPMat);
    1354:   PetscViewerDestroy(&ksp->viewerRhs);
    1355:   PetscViewerDestroy(&ksp->viewerSol);
    1356:   PetscViewerDestroy(&ksp->viewerMatExp);
    1357:   PetscViewerDestroy(&ksp->viewerEV);
    1358:   PetscViewerDestroy(&ksp->viewerSV);
    1359:   PetscViewerDestroy(&ksp->viewerEVExp);
    1360:   PetscViewerDestroy(&ksp->viewerFinalRes);
    1361:   PetscViewerDestroy(&ksp->viewerPOpExp);
    1362:   PetscViewerDestroy(&ksp->viewerDScale);
    1363:   ksp->view         = PETSC_FALSE;
    1364:   ksp->viewPre      = PETSC_FALSE;
    1365:   ksp->viewMat      = PETSC_FALSE;
    1366:   ksp->viewPMat     = PETSC_FALSE;
    1367:   ksp->viewRhs      = PETSC_FALSE;
    1368:   ksp->viewSol      = PETSC_FALSE;
    1369:   ksp->viewMatExp   = PETSC_FALSE;
    1370:   ksp->viewEV       = PETSC_FALSE;
    1371:   ksp->viewSV       = PETSC_FALSE;
    1372:   ksp->viewEVExp    = PETSC_FALSE;
    1373:   ksp->viewFinalRes = PETSC_FALSE;
    1374:   ksp->viewPOpExp   = PETSC_FALSE;
    1375:   ksp->viewDScale   = PETSC_FALSE;
    1376:   return(0);
    1377: }

    1379: /*@
    1380:    KSPReset - Resets a KSP context to the kspsetupcalled = 0 state and removes any allocated Vecs and Mats

    1382:    Collective on ksp

    1384:    Input Parameter:
    1385: .  ksp - iterative context obtained from KSPCreate()

    1387:    Level: beginner

    1389: .seealso: KSPCreate(), KSPSetUp(), KSPSolve(), KSP
    1390: @*/
    1391: PetscErrorCode  KSPReset(KSP ksp)
    1392: {

    1397:   if (!ksp) return(0);
    1398:   if (ksp->ops->reset) {
    1399:     (*ksp->ops->reset)(ksp);
    1400:   }
    1401:   if (ksp->pc) {PCReset(ksp->pc);}
    1402:   if (ksp->guess) {
    1403:     KSPGuess guess = ksp->guess;
    1404:     if (guess->ops->reset) { (*guess->ops->reset)(guess); }
    1405:   }
    1406:   VecDestroyVecs(ksp->nwork,&ksp->work);
    1407:   VecDestroy(&ksp->vec_rhs);
    1408:   VecDestroy(&ksp->vec_sol);
    1409:   VecDestroy(&ksp->diagonal);
    1410:   VecDestroy(&ksp->truediagonal);

    1412:   KSPResetViewers(ksp);

    1414:   ksp->setupstage = KSP_SETUP_NEW;
    1415:   ksp->nmax = PETSC_DECIDE;
    1416:   return(0);
    1417: }

    1419: /*@C
    1420:    KSPDestroy - Destroys KSP context.

    1422:    Collective on ksp

    1424:    Input Parameter:
    1425: .  ksp - iterative context obtained from KSPCreate()

    1427:    Level: beginner

    1429: .seealso: KSPCreate(), KSPSetUp(), KSPSolve(), KSP
    1430: @*/
    1431: PetscErrorCode  KSPDestroy(KSP *ksp)
    1432: {
    1434:   PC             pc;

    1437:   if (!*ksp) return(0);
    1439:   if (--((PetscObject)(*ksp))->refct > 0) {*ksp = NULL; return(0);}

    1441:   PetscObjectSAWsViewOff((PetscObject)*ksp);

    1443:   /*
    1444:    Avoid a cascading call to PCReset(ksp->pc) from the following call:
    1445:    PCReset() shouldn't be called from KSPDestroy() as it is unprotected by pc's
    1446:    refcount (and may be shared, e.g., by other ksps).
    1447:    */
    1448:   pc         = (*ksp)->pc;
    1449:   (*ksp)->pc = NULL;
    1450:   KSPReset((*ksp));
    1451:   (*ksp)->pc = pc;
    1452:   if ((*ksp)->ops->destroy) {(*(*ksp)->ops->destroy)(*ksp);}

    1454:   if ((*ksp)->transpose.use_explicittranspose) {
    1455:     MatDestroy(&(*ksp)->transpose.AT);
    1456:     MatDestroy(&(*ksp)->transpose.BT);
    1457:     (*ksp)->transpose.reuse_transpose = PETSC_FALSE;
    1458:   }

    1460:   KSPGuessDestroy(&(*ksp)->guess);
    1461:   DMDestroy(&(*ksp)->dm);
    1462:   PCDestroy(&(*ksp)->pc);
    1463:   PetscFree((*ksp)->res_hist_alloc);
    1464:   PetscFree((*ksp)->err_hist_alloc);
    1465:   if ((*ksp)->convergeddestroy) {
    1466:     (*(*ksp)->convergeddestroy)((*ksp)->cnvP);
    1467:   }
    1468:   KSPMonitorCancel((*ksp));
    1469:   KSPConvergedReasonViewCancel((*ksp));
    1470:   PetscViewerDestroy(&(*ksp)->eigviewer);
    1471:   PetscHeaderDestroy(ksp);
    1472:   return(0);
    1473: }

    1475: /*@
    1476:     KSPSetPCSide - Sets the preconditioning side.

    1478:     Logically Collective on ksp

    1480:     Input Parameter:
    1481: .   ksp - iterative context obtained from KSPCreate()

    1483:     Output Parameter:
    1484: .   side - the preconditioning side, where side is one of
    1485: .vb
    1486:       PC_LEFT - left preconditioning (default)
    1487:       PC_RIGHT - right preconditioning
    1488:       PC_SYMMETRIC - symmetric preconditioning
    1489: .ve

    1491:     Options Database Keys:
    1492: .   -ksp_pc_side <right,left,symmetric>

    1494:     Notes:
    1495:     Left preconditioning is used by default for most Krylov methods except KSPFGMRES which only supports right preconditioning.

    1497:     For methods changing the side of the preconditioner changes the norm type that is used, see KSPSetNormType().

    1499:     Symmetric preconditioning is currently available only for the KSPQCG method. Note, however, that
    1500:     symmetric preconditioning can be emulated by using either right or left
    1501:     preconditioning and a pre or post processing step.

    1503:     Setting the PC side often affects the default norm type.  See KSPSetNormType() for details.

    1505:     Level: intermediate

    1507: .seealso: KSPGetPCSide(), KSPSetNormType(), KSPGetNormType(), KSP
    1508: @*/
    1509: PetscErrorCode  KSPSetPCSide(KSP ksp,PCSide side)
    1510: {
    1514:   ksp->pc_side = ksp->pc_side_set = side;
    1515:   return(0);
    1516: }

    1518: /*@
    1519:     KSPGetPCSide - Gets the preconditioning side.

    1521:     Not Collective

    1523:     Input Parameter:
    1524: .   ksp - iterative context obtained from KSPCreate()

    1526:     Output Parameter:
    1527: .   side - the preconditioning side, where side is one of
    1528: .vb
    1529:       PC_LEFT - left preconditioning (default)
    1530:       PC_RIGHT - right preconditioning
    1531:       PC_SYMMETRIC - symmetric preconditioning
    1532: .ve

    1534:     Level: intermediate

    1536: .seealso: KSPSetPCSide(), KSP
    1537: @*/
    1538: PetscErrorCode  KSPGetPCSide(KSP ksp,PCSide *side)
    1539: {

    1545:   KSPSetUpNorms_Private(ksp,PETSC_TRUE,&ksp->normtype,&ksp->pc_side);
    1546:   *side = ksp->pc_side;
    1547:   return(0);
    1548: }

    1550: /*@
    1551:    KSPGetTolerances - Gets the relative, absolute, divergence, and maximum
    1552:    iteration tolerances used by the default KSP convergence tests.

    1554:    Not Collective

    1556:    Input Parameter:
    1557: .  ksp - the Krylov subspace context

    1559:    Output Parameters:
    1560: +  rtol - the relative convergence tolerance
    1561: .  abstol - the absolute convergence tolerance
    1562: .  dtol - the divergence tolerance
    1563: -  maxits - maximum number of iterations

    1565:    Notes:
    1566:    The user can specify NULL for any parameter that is not needed.

    1568:    Level: intermediate

    1570:            maximum, iterations

    1572: .seealso: KSPSetTolerances(), KSP
    1573: @*/
    1574: PetscErrorCode  KSPGetTolerances(KSP ksp,PetscReal *rtol,PetscReal *abstol,PetscReal *dtol,PetscInt *maxits)
    1575: {
    1578:   if (abstol) *abstol = ksp->abstol;
    1579:   if (rtol) *rtol = ksp->rtol;
    1580:   if (dtol) *dtol = ksp->divtol;
    1581:   if (maxits) *maxits = ksp->max_it;
    1582:   return(0);
    1583: }

    1585: /*@
    1586:    KSPSetTolerances - Sets the relative, absolute, divergence, and maximum
    1587:    iteration tolerances used by the default KSP convergence testers.

    1589:    Logically Collective on ksp

    1591:    Input Parameters:
    1592: +  ksp - the Krylov subspace context
    1593: .  rtol - the relative convergence tolerance, relative decrease in the (possibly preconditioned) residual norm
    1594: .  abstol - the absolute convergence tolerance   absolute size of the (possibly preconditioned) residual norm
    1595: .  dtol - the divergence tolerance,   amount (possibly preconditioned) residual norm can increase before KSPConvergedDefault() concludes that the method is diverging
    1596: -  maxits - maximum number of iterations to use

    1598:    Options Database Keys:
    1599: +  -ksp_atol <abstol> - Sets abstol
    1600: .  -ksp_rtol <rtol> - Sets rtol
    1601: .  -ksp_divtol <dtol> - Sets dtol
    1602: -  -ksp_max_it <maxits> - Sets maxits

    1604:    Notes:
    1605:    Use PETSC_DEFAULT to retain the default value of any of the tolerances.

    1607:    See KSPConvergedDefault() for details how these parameters are used in the default convergence test.  See also KSPSetConvergenceTest()
    1608:    for setting user-defined stopping criteria.

    1610:    Level: intermediate

    1612:            convergence, maximum, iterations

    1614: .seealso: KSPGetTolerances(), KSPConvergedDefault(), KSPSetConvergenceTest(), KSP
    1615: @*/
    1616: PetscErrorCode  KSPSetTolerances(KSP ksp,PetscReal rtol,PetscReal abstol,PetscReal dtol,PetscInt maxits)
    1617: {

    1625:   if (rtol != PETSC_DEFAULT) {
    1626:     if (rtol < 0.0 || 1.0 <= rtol) SETERRQ1(PetscObjectComm((PetscObject)ksp),PETSC_ERR_ARG_OUTOFRANGE,"Relative tolerance %g must be non-negative and less than 1.0",(double)rtol);
    1627:     ksp->rtol = rtol;
    1628:   }
    1629:   if (abstol != PETSC_DEFAULT) {
    1630:     if (abstol < 0.0) SETERRQ1(PetscObjectComm((PetscObject)ksp),PETSC_ERR_ARG_OUTOFRANGE,"Absolute tolerance %g must be non-negative",(double)abstol);
    1631:     ksp->abstol = abstol;
    1632:   }
    1633:   if (dtol != PETSC_DEFAULT) {
    1634:     if (dtol < 0.0) SETERRQ1(PetscObjectComm((PetscObject)ksp),PETSC_ERR_ARG_OUTOFRANGE,"Divergence tolerance %g must be larger than 1.0",(double)dtol);
    1635:     ksp->divtol = dtol;
    1636:   }
    1637:   if (maxits != PETSC_DEFAULT) {
    1638:     if (maxits < 0) SETERRQ1(PetscObjectComm((PetscObject)ksp),PETSC_ERR_ARG_OUTOFRANGE,"Maximum number of iterations %D must be non-negative",maxits);
    1639:     ksp->max_it = maxits;
    1640:   }
    1641:   return(0);
    1642: }

    1644: /*@
    1645:    KSPSetInitialGuessNonzero - Tells the iterative solver that the
    1646:    initial guess is nonzero; otherwise KSP assumes the initial guess
    1647:    is to be zero (and thus zeros it out before solving).

    1649:    Logically Collective on ksp

    1651:    Input Parameters:
    1652: +  ksp - iterative context obtained from KSPCreate()
    1653: -  flg - PETSC_TRUE indicates the guess is non-zero, PETSC_FALSE indicates the guess is zero

    1655:    Options database keys:
    1656: .  -ksp_initial_guess_nonzero : use nonzero initial guess; this takes an optional truth value (0/1/no/yes/true/false)

    1658:    Level: beginner

    1660:    Notes:
    1661:     If this is not called the X vector is zeroed in the call to KSPSolve().

    1663: .seealso: KSPGetInitialGuessNonzero(), KSPSetGuessType(), KSPGuessType, KSP
    1664: @*/
    1665: PetscErrorCode  KSPSetInitialGuessNonzero(KSP ksp,PetscBool flg)
    1666: {
    1670:   ksp->guess_zero = (PetscBool) !(int)flg;
    1671:   return(0);
    1672: }

    1674: /*@
    1675:    KSPGetInitialGuessNonzero - Determines whether the KSP solver is using
    1676:    a zero initial guess.

    1678:    Not Collective

    1680:    Input Parameter:
    1681: .  ksp - iterative context obtained from KSPCreate()

    1683:    Output Parameter:
    1684: .  flag - PETSC_TRUE if guess is nonzero, else PETSC_FALSE

    1686:    Level: intermediate

    1688: .seealso: KSPSetInitialGuessNonzero(), KSP
    1689: @*/
    1690: PetscErrorCode  KSPGetInitialGuessNonzero(KSP ksp,PetscBool  *flag)
    1691: {
    1695:   if (ksp->guess_zero) *flag = PETSC_FALSE;
    1696:   else *flag = PETSC_TRUE;
    1697:   return(0);
    1698: }

    1700: /*@
    1701:    KSPSetErrorIfNotConverged - Causes KSPSolve() to generate an error if the solver has not converged.

    1703:    Logically Collective on ksp

    1705:    Input Parameters:
    1706: +  ksp - iterative context obtained from KSPCreate()
    1707: -  flg - PETSC_TRUE indicates you want the error generated

    1709:    Options database keys:
    1710: .  -ksp_error_if_not_converged : this takes an optional truth value (0/1/no/yes/true/false)

    1712:    Level: intermediate

    1714:    Notes:
    1715:     Normally PETSc continues if a linear solver fails to converge, you can call KSPGetConvergedReason() after a KSPSolve()
    1716:     to determine if it has converged.

    1719: .seealso: KSPGetErrorIfNotConverged(), KSP
    1720: @*/
    1721: PetscErrorCode  KSPSetErrorIfNotConverged(KSP ksp,PetscBool flg)
    1722: {
    1726:   ksp->errorifnotconverged = flg;
    1727:   return(0);
    1728: }

    1730: /*@
    1731:    KSPGetErrorIfNotConverged - Will KSPSolve() generate an error if the solver does not converge?

    1733:    Not Collective

    1735:    Input Parameter:
    1736: .  ksp - iterative context obtained from KSPCreate()

    1738:    Output Parameter:
    1739: .  flag - PETSC_TRUE if it will generate an error, else PETSC_FALSE

    1741:    Level: intermediate

    1743: .seealso: KSPSetErrorIfNotConverged(), KSP
    1744: @*/
    1745: PetscErrorCode  KSPGetErrorIfNotConverged(KSP ksp,PetscBool  *flag)
    1746: {
    1750:   *flag = ksp->errorifnotconverged;
    1751:   return(0);
    1752: }

    1754: /*@
    1755:    KSPSetInitialGuessKnoll - Tells the iterative solver to use PCApply(pc,b,..) to compute the initial guess (The Knoll trick)

    1757:    Logically Collective on ksp

    1759:    Input Parameters:
    1760: +  ksp - iterative context obtained from KSPCreate()
    1761: -  flg - PETSC_TRUE or PETSC_FALSE

    1763:    Level: advanced

    1765:    Developer Note: the Knoll trick is not currently implemented using the KSPGuess class

    1767: .seealso: KSPGetInitialGuessKnoll(), KSPSetInitialGuessNonzero(), KSPGetInitialGuessNonzero(), KSP
    1768: @*/
    1769: PetscErrorCode  KSPSetInitialGuessKnoll(KSP ksp,PetscBool flg)
    1770: {
    1774:   ksp->guess_knoll = flg;
    1775:   return(0);
    1776: }

    1778: /*@
    1779:    KSPGetInitialGuessKnoll - Determines whether the KSP solver is using the Knoll trick (using PCApply(pc,b,...) to compute
    1780:      the initial guess

    1782:    Not Collective

    1784:    Input Parameter:
    1785: .  ksp - iterative context obtained from KSPCreate()

    1787:    Output Parameter:
    1788: .  flag - PETSC_TRUE if using Knoll trick, else PETSC_FALSE

    1790:    Level: advanced

    1792: .seealso: KSPSetInitialGuessKnoll(), KSPSetInitialGuessNonzero(), KSPGetInitialGuessNonzero(), KSP
    1793: @*/
    1794: PetscErrorCode  KSPGetInitialGuessKnoll(KSP ksp,PetscBool  *flag)
    1795: {
    1799:   *flag = ksp->guess_knoll;
    1800:   return(0);
    1801: }

    1803: /*@
    1804:    KSPGetComputeSingularValues - Gets the flag indicating whether the extreme singular
    1805:    values will be calculated via a Lanczos or Arnoldi process as the linear
    1806:    system is solved.

    1808:    Not Collective

    1810:    Input Parameter:
    1811: .  ksp - iterative context obtained from KSPCreate()

    1813:    Output Parameter:
    1814: .  flg - PETSC_TRUE or PETSC_FALSE

    1816:    Options Database Key:
    1817: .  -ksp_monitor_singular_value - Activates KSPSetComputeSingularValues()

    1819:    Notes:
    1820:    Currently this option is not valid for all iterative methods.

    1822:    Many users may just want to use the monitoring routine
    1823:    KSPMonitorSingularValue() (which can be set with option -ksp_monitor_singular_value)
    1824:    to print the singular values at each iteration of the linear solve.

    1826:    Level: advanced

    1828: .seealso: KSPComputeExtremeSingularValues(), KSPMonitorSingularValue(), KSP
    1829: @*/
    1830: PetscErrorCode  KSPGetComputeSingularValues(KSP ksp,PetscBool  *flg)
    1831: {
    1835:   *flg = ksp->calc_sings;
    1836:   return(0);
    1837: }

    1839: /*@
    1840:    KSPSetComputeSingularValues - Sets a flag so that the extreme singular
    1841:    values will be calculated via a Lanczos or Arnoldi process as the linear
    1842:    system is solved.

    1844:    Logically Collective on ksp

    1846:    Input Parameters:
    1847: +  ksp - iterative context obtained from KSPCreate()
    1848: -  flg - PETSC_TRUE or PETSC_FALSE

    1850:    Options Database Key:
    1851: .  -ksp_monitor_singular_value - Activates KSPSetComputeSingularValues()

    1853:    Notes:
    1854:    Currently this option is not valid for all iterative methods.

    1856:    Many users may just want to use the monitoring routine
    1857:    KSPMonitorSingularValue() (which can be set with option -ksp_monitor_singular_value)
    1858:    to print the singular values at each iteration of the linear solve.

    1860:    Level: advanced

    1862: .seealso: KSPComputeExtremeSingularValues(), KSPMonitorSingularValue(), KSP
    1863: @*/
    1864: PetscErrorCode  KSPSetComputeSingularValues(KSP ksp,PetscBool flg)
    1865: {
    1869:   ksp->calc_sings = flg;
    1870:   return(0);
    1871: }

    1873: /*@
    1874:    KSPGetComputeEigenvalues - Gets the flag indicating that the extreme eigenvalues
    1875:    values will be calculated via a Lanczos or Arnoldi process as the linear
    1876:    system is solved.

    1878:    Not Collective

    1880:    Input Parameter:
    1881: .  ksp - iterative context obtained from KSPCreate()

    1883:    Output Parameter:
    1884: .  flg - PETSC_TRUE or PETSC_FALSE

    1886:    Notes:
    1887:    Currently this option is not valid for all iterative methods.

    1889:    Level: advanced

    1891: .seealso: KSPComputeEigenvalues(), KSPComputeEigenvaluesExplicitly(), KSP
    1892: @*/
    1893: PetscErrorCode  KSPGetComputeEigenvalues(KSP ksp,PetscBool  *flg)
    1894: {
    1898:   *flg = ksp->calc_sings;
    1899:   return(0);
    1900: }

    1902: /*@
    1903:    KSPSetComputeEigenvalues - Sets a flag so that the extreme eigenvalues
    1904:    values will be calculated via a Lanczos or Arnoldi process as the linear
    1905:    system is solved.

    1907:    Logically Collective on ksp

    1909:    Input Parameters:
    1910: +  ksp - iterative context obtained from KSPCreate()
    1911: -  flg - PETSC_TRUE or PETSC_FALSE

    1913:    Notes:
    1914:    Currently this option is not valid for all iterative methods.

    1916:    Level: advanced

    1918: .seealso: KSPComputeEigenvalues(), KSPComputeEigenvaluesExplicitly(), KSP
    1919: @*/
    1920: PetscErrorCode  KSPSetComputeEigenvalues(KSP ksp,PetscBool flg)
    1921: {
    1925:   ksp->calc_sings = flg;
    1926:   return(0);
    1927: }

    1929: /*@
    1930:    KSPSetComputeRitz - Sets a flag so that the Ritz or harmonic Ritz pairs
    1931:    will be calculated via a Lanczos or Arnoldi process as the linear
    1932:    system is solved.

    1934:    Logically Collective on ksp

    1936:    Input Parameters:
    1937: +  ksp - iterative context obtained from KSPCreate()
    1938: -  flg - PETSC_TRUE or PETSC_FALSE

    1940:    Notes:
    1941:    Currently this option is only valid for the GMRES method.

    1943:    Level: advanced

    1945: .seealso: KSPComputeRitz(), KSP
    1946: @*/
    1947: PetscErrorCode  KSPSetComputeRitz(KSP ksp, PetscBool flg)
    1948: {
    1952:   ksp->calc_ritz = flg;
    1953:   return(0);
    1954: }

    1956: /*@
    1957:    KSPGetRhs - Gets the right-hand-side vector for the linear system to
    1958:    be solved.

    1960:    Not Collective

    1962:    Input Parameter:
    1963: .  ksp - iterative context obtained from KSPCreate()

    1965:    Output Parameter:
    1966: .  r - right-hand-side vector

    1968:    Level: developer

    1970: .seealso: KSPGetSolution(), KSPSolve(), KSP
    1971: @*/
    1972: PetscErrorCode  KSPGetRhs(KSP ksp,Vec *r)
    1973: {
    1977:   *r = ksp->vec_rhs;
    1978:   return(0);
    1979: }

    1981: /*@
    1982:    KSPGetSolution - Gets the location of the solution for the
    1983:    linear system to be solved.  Note that this may not be where the solution
    1984:    is stored during the iterative process; see KSPBuildSolution().

    1986:    Not Collective

    1988:    Input Parameters:
    1989: .  ksp - iterative context obtained from KSPCreate()

    1991:    Output Parameters:
    1992: .  v - solution vector

    1994:    Level: developer

    1996: .seealso: KSPGetRhs(),  KSPBuildSolution(), KSPSolve(), KSP
    1997: @*/
    1998: PetscErrorCode  KSPGetSolution(KSP ksp,Vec *v)
    1999: {
    2003:   *v = ksp->vec_sol;
    2004:   return(0);
    2005: }

    2007: /*@
    2008:    KSPSetPC - Sets the preconditioner to be used to calculate the
    2009:    application of the preconditioner on a vector.

    2011:    Collective on ksp

    2013:    Input Parameters:
    2014: +  ksp - iterative context obtained from KSPCreate()
    2015: -  pc   - the preconditioner object (can be NULL)

    2017:    Notes:
    2018:    Use KSPGetPC() to retrieve the preconditioner context.

    2020:    Level: developer

    2022: .seealso: KSPGetPC(), KSP
    2023: @*/
    2024: PetscErrorCode  KSPSetPC(KSP ksp,PC pc)
    2025: {

    2030:   if (pc) {
    2033:   }
    2034:   PetscObjectReference((PetscObject)pc);
    2035:   PCDestroy(&ksp->pc);
    2036:   ksp->pc = pc;
    2037:   PetscLogObjectParent((PetscObject)ksp,(PetscObject)ksp->pc);
    2038:   return(0);
    2039: }

    2041: /*@
    2042:    KSPGetPC - Returns a pointer to the preconditioner context
    2043:    set with KSPSetPC().

    2045:    Not Collective

    2047:    Input Parameters:
    2048: .  ksp - iterative context obtained from KSPCreate()

    2050:    Output Parameter:
    2051: .  pc - preconditioner context

    2053:    Level: developer

    2055: .seealso: KSPSetPC(), KSP
    2056: @*/
    2057: PetscErrorCode  KSPGetPC(KSP ksp,PC *pc)
    2058: {

    2064:   if (!ksp->pc) {
    2065:     PCCreate(PetscObjectComm((PetscObject)ksp),&ksp->pc);
    2066:     PetscObjectIncrementTabLevel((PetscObject)ksp->pc,(PetscObject)ksp,0);
    2067:     PetscLogObjectParent((PetscObject)ksp,(PetscObject)ksp->pc);
    2068:     PetscObjectSetOptions((PetscObject)ksp->pc,((PetscObject)ksp)->options);
    2069:   }
    2070:   *pc = ksp->pc;
    2071:   return(0);
    2072: }

    2074: /*@
    2075:    KSPMonitor - runs the user provided monitor routines, if they exist

    2077:    Collective on ksp

    2079:    Input Parameters:
    2080: +  ksp - iterative context obtained from KSPCreate()
    2081: .  it - iteration number
    2082: -  rnorm - relative norm of the residual

    2084:    Notes:
    2085:    This routine is called by the KSP implementations.
    2086:    It does not typically need to be called by the user.

    2088:    Level: developer

    2090: .seealso: KSPMonitorSet()
    2091: @*/
    2092: PetscErrorCode KSPMonitor(KSP ksp,PetscInt it,PetscReal rnorm)
    2093: {
    2094:   PetscInt       i, n = ksp->numbermonitors;

    2098:   for (i=0; i<n; i++) {
    2099:     (*ksp->monitor[i])(ksp,it,rnorm,ksp->monitorcontext[i]);
    2100:   }
    2101:   return(0);
    2102: }

    2104: /*@C
    2105:    KSPMonitorSet - Sets an ADDITIONAL function to be called at every iteration to monitor
    2106:    the residual/error etc.

    2108:    Logically Collective on ksp

    2110:    Input Parameters:
    2111: +  ksp - iterative context obtained from KSPCreate()
    2112: .  monitor - pointer to function (if this is NULL, it turns off monitoring
    2113: .  mctx    - [optional] context for private data for the
    2114:              monitor routine (use NULL if no context is desired)
    2115: -  monitordestroy - [optional] routine that frees monitor context
    2116:           (may be NULL)

    2118:    Calling Sequence of monitor:
    2119: $     monitor (KSP ksp, PetscInt it, PetscReal rnorm, void *mctx)

    2121: +  ksp - iterative context obtained from KSPCreate()
    2122: .  it - iteration number
    2123: .  rnorm - (estimated) 2-norm of (preconditioned) residual
    2124: -  mctx  - optional monitoring context, as set by KSPMonitorSet()

    2126:    Options Database Keys:
    2127: +    -ksp_monitor               - sets KSPMonitorResidual()
    2128: .    -ksp_monitor draw          - sets KSPMonitorResidualDraw() and plots residual
    2129: .    -ksp_monitor draw::draw_lg - sets KSPMonitorResidualDrawLG() and plots residual
    2130: .    -ksp_monitor_pause_final   - Pauses any graphics when the solve finishes (only works for internal monitors)
    2131: .    -ksp_monitor_true_residual - sets KSPMonitorTrueResidual()
    2132: .    -ksp_monitor_true_residual draw::draw_lg - sets KSPMonitorTrueResidualDrawLG() and plots residual
    2133: .    -ksp_monitor_max           - sets KSPMonitorTrueResidualMax()
    2134: .    -ksp_monitor_singular_value - sets KSPMonitorSingularValue()
    2135: -    -ksp_monitor_cancel - cancels all monitors that have
    2136:                           been hardwired into a code by
    2137:                           calls to KSPMonitorSet(), but
    2138:                           does not cancel those set via
    2139:                           the options database.

    2141:    Notes:
    2142:    The default is to do nothing.  To print the residual, or preconditioned
    2143:    residual if KSPSetNormType(ksp,KSP_NORM_PRECONDITIONED) was called, use
    2144:    KSPMonitorResidual() as the monitoring routine, with a ASCII viewer as the
    2145:    context.

    2147:    Several different monitoring routines may be set by calling
    2148:    KSPMonitorSet() multiple times; all will be called in the
    2149:    order in which they were set.

    2151:    Fortran Notes:
    2152:     Only a single monitor function can be set for each KSP object

    2154:    Level: beginner

    2156: .seealso: KSPMonitorResidual(), KSPMonitorCancel(), KSP
    2157: @*/
    2158: PetscErrorCode  KSPMonitorSet(KSP ksp,PetscErrorCode (*monitor)(KSP,PetscInt,PetscReal,void*),void *mctx,PetscErrorCode (*monitordestroy)(void**))
    2159: {
    2160:   PetscInt       i;
    2162:   PetscBool      identical;

    2166:   for (i=0; i<ksp->numbermonitors;i++) {
    2167:     PetscMonitorCompare((PetscErrorCode (*)(void))monitor,mctx,monitordestroy,(PetscErrorCode (*)(void))ksp->monitor[i],ksp->monitorcontext[i],ksp->monitordestroy[i],&identical);
    2168:     if (identical) return(0);
    2169:   }
    2170:   if (ksp->numbermonitors >= MAXKSPMONITORS) SETERRQ(PetscObjectComm((PetscObject)ksp),PETSC_ERR_ARG_OUTOFRANGE,"Too many KSP monitors set");
    2171:   ksp->monitor[ksp->numbermonitors]          = monitor;
    2172:   ksp->monitordestroy[ksp->numbermonitors]   = monitordestroy;
    2173:   ksp->monitorcontext[ksp->numbermonitors++] = (void*)mctx;
    2174:   return(0);
    2175: }

    2177: /*@
    2178:    KSPMonitorCancel - Clears all monitors for a KSP object.

    2180:    Logically Collective on ksp

    2182:    Input Parameters:
    2183: .  ksp - iterative context obtained from KSPCreate()

    2185:    Options Database Key:
    2186: .  -ksp_monitor_cancel - Cancels all monitors that have
    2187:     been hardwired into a code by calls to KSPMonitorSet(),
    2188:     but does not cancel those set via the options database.

    2190:    Level: intermediate

    2192: .seealso: KSPMonitorResidual(), KSPMonitorSet(), KSP
    2193: @*/
    2194: PetscErrorCode  KSPMonitorCancel(KSP ksp)
    2195: {
    2197:   PetscInt       i;

    2201:   for (i=0; i<ksp->numbermonitors; i++) {
    2202:     if (ksp->monitordestroy[i]) {
    2203:       (*ksp->monitordestroy[i])(&ksp->monitorcontext[i]);
    2204:     }
    2205:   }
    2206:   ksp->numbermonitors = 0;
    2207:   return(0);
    2208: }

    2210: /*@C
    2211:    KSPGetMonitorContext - Gets the monitoring context, as set by
    2212:    KSPMonitorSet() for the FIRST monitor only.

    2214:    Not Collective

    2216:    Input Parameter:
    2217: .  ksp - iterative context obtained from KSPCreate()

    2219:    Output Parameter:
    2220: .  ctx - monitoring context

    2222:    Level: intermediate

    2224: .seealso: KSPMonitorResidual(), KSP
    2225: @*/
    2226: PetscErrorCode  KSPGetMonitorContext(KSP ksp,void **ctx)
    2227: {
    2230:   *ctx =      (ksp->monitorcontext[0]);
    2231:   return(0);
    2232: }

    2234: /*@
    2235:    KSPSetResidualHistory - Sets the array used to hold the residual history.
    2236:    If set, this array will contain the residual norms computed at each
    2237:    iteration of the solver.

    2239:    Not Collective

    2241:    Input Parameters:
    2242: +  ksp - iterative context obtained from KSPCreate()
    2243: .  a   - array to hold history
    2244: .  na  - size of a
    2245: -  reset - PETSC_TRUE indicates the history counter is reset to zero
    2246:            for each new linear solve

    2248:    Level: advanced

    2250:    Notes:
    2251:    If provided, he array is NOT freed by PETSc so the user needs to keep track of it and destroy once the KSP object is destroyed.
    2252:    If 'a' is NULL then space is allocated for the history. If 'na' PETSC_DECIDE or PETSC_DEFAULT then a
    2253:    default array of length 10000 is allocated.

    2255: .seealso: KSPGetResidualHistory(), KSP

    2257: @*/
    2258: PetscErrorCode KSPSetResidualHistory(KSP ksp,PetscReal a[],PetscInt na,PetscBool reset)
    2259: {

    2265:   PetscFree(ksp->res_hist_alloc);
    2266:   if (na != PETSC_DECIDE && na != PETSC_DEFAULT && a) {
    2267:     ksp->res_hist     = a;
    2268:     ksp->res_hist_max = na;
    2269:   } else {
    2270:     if (na != PETSC_DECIDE && na != PETSC_DEFAULT) ksp->res_hist_max = na;
    2271:     else                                           ksp->res_hist_max = 10000; /* like default ksp->max_it */
    2272:     PetscCalloc1(ksp->res_hist_max,&ksp->res_hist_alloc);

    2274:     ksp->res_hist = ksp->res_hist_alloc;
    2275:   }
    2276:   ksp->res_hist_len   = 0;
    2277:   ksp->res_hist_reset = reset;
    2278:   return(0);
    2279: }

    2281: /*@C
    2282:    KSPGetResidualHistory - Gets the array used to hold the residual history
    2283:    and the number of residuals it contains.

    2285:    Not Collective

    2287:    Input Parameter:
    2288: .  ksp - iterative context obtained from KSPCreate()

    2290:    Output Parameters:
    2291: +  a   - pointer to array to hold history (or NULL)
    2292: -  na  - number of used entries in a (or NULL)

    2294:    Level: advanced

    2296:    Notes:
    2297:      This array is borrowed and should not be freed by the caller.
    2298:      Can only be called after a KSPSetResidualHistory() otherwise a and na are set to zero

    2300:      The Fortran version of this routine has a calling sequence
    2301: $   call KSPGetResidualHistory(KSP ksp, integer na, integer ierr)
    2302:     note that you have passed a Fortran array into KSPSetResidualHistory() and you need
    2303:     to access the residual values from this Fortran array you provided. Only the na (number of
    2304:     residual norms currently held) is set.

    2306: .seealso: KSPSetResidualHistory(), KSP

    2308: @*/
    2309: PetscErrorCode KSPGetResidualHistory(KSP ksp, const PetscReal *a[],PetscInt *na)
    2310: {
    2313:   if (a) *a = ksp->res_hist;
    2314:   if (na) *na = ksp->res_hist_len;
    2315:   return(0);
    2316: }

    2318: /*@
    2319:   KSPSetErrorHistory - Sets the array used to hold the error history. If set, this array will contain the error norms computed at each iteration of the solver.

    2321:   Not Collective

    2323:   Input Parameters:
    2324: + ksp   - iterative context obtained from KSPCreate()
    2325: . a     - array to hold history
    2326: . na    - size of a
    2327: - reset - PETSC_TRUE indicates the history counter is reset to zero for each new linear solve

    2329:   Level: advanced

    2331:   Notes:
    2332:   If provided, the array is NOT freed by PETSc so the user needs to keep track of it and destroy once the KSP object is destroyed.
    2333:   If 'a' is NULL then space is allocated for the history. If 'na' PETSC_DECIDE or PETSC_DEFAULT then a default array of length 10000 is allocated.

    2335: .seealso: KSPGetErrorHistory(), KSPSetResidualHistory(), KSP
    2336: @*/
    2337: PetscErrorCode KSPSetErrorHistory(KSP ksp, PetscReal a[], PetscInt na, PetscBool reset)
    2338: {

    2344:   PetscFree(ksp->err_hist_alloc);
    2345:   if (na != PETSC_DECIDE && na != PETSC_DEFAULT && a) {
    2346:     ksp->err_hist     = a;
    2347:     ksp->err_hist_max = na;
    2348:   } else {
    2349:     if (na != PETSC_DECIDE && na != PETSC_DEFAULT) ksp->err_hist_max = na;
    2350:     else                                           ksp->err_hist_max = 10000; /* like default ksp->max_it */
    2351:     PetscCalloc1(ksp->err_hist_max, &ksp->err_hist_alloc);

    2353:     ksp->err_hist = ksp->err_hist_alloc;
    2354:   }
    2355:   ksp->err_hist_len   = 0;
    2356:   ksp->err_hist_reset = reset;
    2357:   return(0);
    2358: }

    2360: /*@C
    2361:   KSPGetErrorHistory - Gets the array used to hold the error history and the number of residuals it contains.

    2363:   Not Collective

    2365:   Input Parameter:
    2366: . ksp - iterative context obtained from KSPCreate()

    2368:   Output Parameters:
    2369: + a  - pointer to array to hold history (or NULL)
    2370: - na - number of used entries in a (or NULL)

    2372:   Level: advanced

    2374:   Notes:
    2375:   This array is borrowed and should not be freed by the caller.
    2376:   Can only be called after a KSPSetErrorHistory() otherwise a and na are set to zero
    2377:   The Fortran version of this routine has a calling sequence
    2378: $   call KSPGetErrorHistory(KSP ksp, integer na, integer ierr)
    2379:   note that you have passed a Fortran array into KSPSetErrorHistory() and you need
    2380:   to access the residual values from this Fortran array you provided. Only the na (number of
    2381:   residual norms currently held) is set.

    2383: .seealso: KSPSetErrorHistory(), KSPGetResidualHistory(), KSP
    2384: @*/
    2385: PetscErrorCode KSPGetErrorHistory(KSP ksp, const PetscReal *a[], PetscInt *na)
    2386: {
    2389:   if (a)  *a  = ksp->err_hist;
    2390:   if (na) *na = ksp->err_hist_len;
    2391:   return(0);
    2392: }

    2394: /*
    2395:   KSPComputeConvergenceRate - Compute the convergence rate for the iteration

    2397:   Not collective

    2399:   Input Parameter:
    2400: . ksp - The KSP

    2402:   Output Parameters:
    2403: + cr   - The residual contraction rate
    2404: . rRsq - The coefficient of determination, R^2, indicating the linearity of the data
    2405: . ce   - The error contraction rate
    2406: - eRsq - The coefficient of determination, R^2, indicating the linearity of the data

    2408:   Note:
    2409:   Suppose that the residual is reduced linearly, $r_k = c^k r_0$, which means $log r_k = log r_0 + k log c$. After linear regression,
    2410:   the slope is $\log c$. The coefficient of determination is given by $1 - \frac{\sum_i (y_i - f(x_i))^2}{\sum_i (y_i - \bar y)}$,
    2411:   see also https://en.wikipedia.org/wiki/Coefficient_of_determination

    2413:   Level: advanced

    2415: .seealso: KSPConvergedRateView()
    2416: */
    2417: PetscErrorCode KSPComputeConvergenceRate(KSP ksp, PetscReal *cr, PetscReal *rRsq, PetscReal *ce, PetscReal *eRsq)
    2418: {
    2419:   PetscReal      const *hist;
    2420:   PetscReal      *x, *y, slope, intercept, mean = 0.0, var = 0.0, res = 0.0;
    2421:   PetscInt       n, k;

    2425:   if (cr || rRsq) {
    2426:     KSPGetResidualHistory(ksp, &hist, &n);
    2427:     if (!n) {
    2428:       if (cr)   *cr   =  0.0;
    2429:       if (rRsq) *rRsq = -1.0;
    2430:     } else {
    2431:       PetscMalloc2(n, &x, n, &y);
    2432:       for (k = 0; k < n; ++k) {
    2433:         x[k] = k;
    2434:         y[k] = PetscLogReal(hist[k]);
    2435:         mean += y[k];
    2436:       }
    2437:       mean /= n;
    2438:       PetscLinearRegression(n, x, y, &slope, &intercept);
    2439:       for (k = 0; k < n; ++k) {
    2440:         res += PetscSqr(y[k] - (slope*x[k] + intercept));
    2441:         var += PetscSqr(y[k] - mean);
    2442:       }
    2443:       PetscFree2(x, y);
    2444:       if (cr)   *cr   = PetscExpReal(slope);
    2445:       if (rRsq) *rRsq = var < PETSC_MACHINE_EPSILON ? 0.0 : 1.0 - (res / var);
    2446:     }
    2447:   }
    2448:   if (ce || eRsq) {
    2449:     KSPGetErrorHistory(ksp, &hist, &n);
    2450:     if (!n) {
    2451:       if (ce)   *ce   =  0.0;
    2452:       if (eRsq) *eRsq = -1.0;
    2453:     } else {
    2454:       PetscMalloc2(n, &x, n, &y);
    2455:       for (k = 0; k < n; ++k) {
    2456:         x[k] = k;
    2457:         y[k] = PetscLogReal(hist[k]);
    2458:         mean += y[k];
    2459:       }
    2460:       mean /= n;
    2461:       PetscLinearRegression(n, x, y, &slope, &intercept);
    2462:       for (k = 0; k < n; ++k) {
    2463:         res += PetscSqr(y[k] - (slope*x[k] + intercept));
    2464:         var += PetscSqr(y[k] - mean);
    2465:       }
    2466:       PetscFree2(x, y);
    2467:       if (ce)   *ce   = PetscExpReal(slope);
    2468:       if (eRsq) *eRsq = var < PETSC_MACHINE_EPSILON ? 0.0 : 1.0 - (res / var);
    2469:     }
    2470:   }
    2471:   return(0);
    2472: }

    2474: /*@C
    2475:    KSPSetConvergenceTest - Sets the function to be used to determine
    2476:    convergence.

    2478:    Logically Collective on ksp

    2480:    Input Parameters:
    2481: +  ksp - iterative context obtained from KSPCreate()
    2482: .  converge - pointer to the function
    2483: .  cctx    - context for private data for the convergence routine (may be null)
    2484: -  destroy - a routine for destroying the context (may be null)

    2486:    Calling sequence of converge:
    2487: $     converge (KSP ksp, PetscInt it, PetscReal rnorm, KSPConvergedReason *reason,void *mctx)

    2489: +  ksp - iterative context obtained from KSPCreate()
    2490: .  it - iteration number
    2491: .  rnorm - (estimated) 2-norm of (preconditioned) residual
    2492: .  reason - the reason why it has converged or diverged
    2493: -  cctx  - optional convergence context, as set by KSPSetConvergenceTest()

    2496:    Notes:
    2497:    Must be called after the KSP type has been set so put this after
    2498:    a call to KSPSetType(), or KSPSetFromOptions().

    2500:    The default convergence test, KSPConvergedDefault(), aborts if the
    2501:    residual grows to more than 10000 times the initial residual.

    2503:    The default is a combination of relative and absolute tolerances.
    2504:    The residual value that is tested may be an approximation; routines
    2505:    that need exact values should compute them.

    2507:    In the default PETSc convergence test, the precise values of reason
    2508:    are macros such as KSP_CONVERGED_RTOL, which are defined in petscksp.h.

    2510:    Level: advanced

    2512: .seealso: KSPConvergedDefault(), KSPGetConvergenceContext(), KSPSetTolerances(), KSP, KSPGetConvergenceTest(), KSPGetAndClearConvergenceTest()
    2513: @*/
    2514: PetscErrorCode  KSPSetConvergenceTest(KSP ksp,PetscErrorCode (*converge)(KSP,PetscInt,PetscReal,KSPConvergedReason*,void*),void *cctx,PetscErrorCode (*destroy)(void*))
    2515: {

    2520:   if (ksp->convergeddestroy) {
    2521:     (*ksp->convergeddestroy)(ksp->cnvP);
    2522:   }
    2523:   ksp->converged        = converge;
    2524:   ksp->convergeddestroy = destroy;
    2525:   ksp->cnvP             = (void*)cctx;
    2526:   return(0);
    2527: }

    2529: /*@C
    2530:    KSPGetConvergenceTest - Gets the function to be used to determine
    2531:    convergence.

    2533:    Logically Collective on ksp

    2535:    Input Parameter:
    2536: .   ksp - iterative context obtained from KSPCreate()

    2538:    Output Parameter:
    2539: +  converge - pointer to convergence test function
    2540: .  cctx    - context for private data for the convergence routine (may be null)
    2541: -  destroy - a routine for destroying the context (may be null)

    2543:    Calling sequence of converge:
    2544: $     converge (KSP ksp, PetscInt it, PetscReal rnorm, KSPConvergedReason *reason,void *mctx)

    2546: +  ksp - iterative context obtained from KSPCreate()
    2547: .  it - iteration number
    2548: .  rnorm - (estimated) 2-norm of (preconditioned) residual
    2549: .  reason - the reason why it has converged or diverged
    2550: -  cctx  - optional convergence context, as set by KSPSetConvergenceTest()

    2552:    Level: advanced

    2554: .seealso: KSPConvergedDefault(), KSPGetConvergenceContext(), KSPSetTolerances(), KSP, KSPSetConvergenceTest(), KSPGetAndClearConvergenceTest()
    2555: @*/
    2556: PetscErrorCode  KSPGetConvergenceTest(KSP ksp,PetscErrorCode (**converge)(KSP,PetscInt,PetscReal,KSPConvergedReason*,void*),void **cctx,PetscErrorCode (**destroy)(void*))
    2557: {
    2560:   if (converge) *converge = ksp->converged;
    2561:   if (destroy)  *destroy  = ksp->convergeddestroy;
    2562:   if (cctx)     *cctx     = ksp->cnvP;
    2563:   return(0);
    2564: }

    2566: /*@C
    2567:    KSPGetAndClearConvergenceTest - Gets the function to be used to determine convergence. Removes the current test without calling destroy on the test context

    2569:    Logically Collective on ksp

    2571:    Input Parameter:
    2572: .   ksp - iterative context obtained from KSPCreate()

    2574:    Output Parameter:
    2575: +  converge - pointer to convergence test function
    2576: .  cctx    - context for private data for the convergence routine
    2577: -  destroy - a routine for destroying the context

    2579:    Calling sequence of converge:
    2580: $     converge (KSP ksp, PetscInt it, PetscReal rnorm, KSPConvergedReason *reason,void *mctx)

    2582: +  ksp - iterative context obtained from KSPCreate()
    2583: .  it - iteration number
    2584: .  rnorm - (estimated) 2-norm of (preconditioned) residual
    2585: .  reason - the reason why it has converged or diverged
    2586: -  cctx  - optional convergence context, as set by KSPSetConvergenceTest()

    2588:    Level: advanced

    2590:    Notes: This is intended to be used to allow transferring the convergence test (and its context) to another testing object (for example another KSP) and then calling
    2591:           KSPSetConvergenceTest() on this original KSP. If you just called KSPGetConvergenceTest() followed by KSPSetConvergenceTest() the original context information
    2592:           would be destroyed and hence the transferred context would be invalid and trigger a crash on use

    2594: .seealso: KSPConvergedDefault(), KSPGetConvergenceContext(), KSPSetTolerances(), KSP, KSPSetConvergenceTest(), KSPGetConvergenceTest()
    2595: @*/
    2596: PetscErrorCode  KSPGetAndClearConvergenceTest(KSP ksp,PetscErrorCode (**converge)(KSP,PetscInt,PetscReal,KSPConvergedReason*,void*),void **cctx,PetscErrorCode (**destroy)(void*))
    2597: {
    2600:   *converge             = ksp->converged;
    2601:   *destroy              = ksp->convergeddestroy;
    2602:   *cctx                 = ksp->cnvP;
    2603:   ksp->converged        = NULL;
    2604:   ksp->cnvP             = NULL;
    2605:   ksp->convergeddestroy = NULL;
    2606:   return(0);
    2607: }

    2609: /*@C
    2610:    KSPGetConvergenceContext - Gets the convergence context set with
    2611:    KSPSetConvergenceTest().

    2613:    Not Collective

    2615:    Input Parameter:
    2616: .  ksp - iterative context obtained from KSPCreate()

    2618:    Output Parameter:
    2619: .  ctx - monitoring context

    2621:    Level: advanced

    2623: .seealso: KSPConvergedDefault(), KSPSetConvergenceTest(), KSP
    2624: @*/
    2625: PetscErrorCode  KSPGetConvergenceContext(KSP ksp,void **ctx)
    2626: {
    2629:   *ctx = ksp->cnvP;
    2630:   return(0);
    2631: }

    2633: /*@C
    2634:    KSPBuildSolution - Builds the approximate solution in a vector provided.
    2635:    This routine is NOT commonly needed (see KSPSolve()).

    2637:    Collective on ksp

    2639:    Input Parameter:
    2640: .  ctx - iterative context obtained from KSPCreate()

    2642:    Output Parameter:
    2643:    Provide exactly one of
    2644: +  v - location to stash solution.
    2645: -  V - the solution is returned in this location. This vector is created
    2646:        internally. This vector should NOT be destroyed by the user with
    2647:        VecDestroy().

    2649:    Notes:
    2650:    This routine can be used in one of two ways
    2651: .vb
    2652:       KSPBuildSolution(ksp,NULL,&V);
    2653:    or
    2654:       KSPBuildSolution(ksp,v,NULL); or KSPBuildSolution(ksp,v,&v);
    2655: .ve
    2656:    In the first case an internal vector is allocated to store the solution
    2657:    (the user cannot destroy this vector). In the second case the solution
    2658:    is generated in the vector that the user provides. Note that for certain
    2659:    methods, such as KSPCG, the second case requires a copy of the solution,
    2660:    while in the first case the call is essentially free since it simply
    2661:    returns the vector where the solution already is stored. For some methods
    2662:    like GMRES this is a reasonably expensive operation and should only be
    2663:    used in truly needed.

    2665:    Level: advanced

    2667: .seealso: KSPGetSolution(), KSPBuildResidual(), KSP
    2668: @*/
    2669: PetscErrorCode  KSPBuildSolution(KSP ksp,Vec v,Vec *V)
    2670: {

    2675:   if (!V && !v) SETERRQ(PetscObjectComm((PetscObject)ksp),PETSC_ERR_ARG_WRONG,"Must provide either v or V");
    2676:   if (!V) V = &v;
    2677:   (*ksp->ops->buildsolution)(ksp,v,V);
    2678:   return(0);
    2679: }

    2681: /*@C
    2682:    KSPBuildResidual - Builds the residual in a vector provided.

    2684:    Collective on ksp

    2686:    Input Parameter:
    2687: .  ksp - iterative context obtained from KSPCreate()

    2689:    Output Parameters:
    2690: +  v - optional location to stash residual.  If v is not provided,
    2691:        then a location is generated.
    2692: .  t - work vector.  If not provided then one is generated.
    2693: -  V - the residual

    2695:    Notes:
    2696:    Regardless of whether or not v is provided, the residual is
    2697:    returned in V.

    2699:    Level: advanced

    2701: .seealso: KSPBuildSolution()
    2702: @*/
    2703: PetscErrorCode  KSPBuildResidual(KSP ksp,Vec t,Vec v,Vec *V)
    2704: {
    2706:   PetscBool      flag = PETSC_FALSE;
    2707:   Vec            w    = v,tt = t;

    2711:   if (!w) {
    2712:     VecDuplicate(ksp->vec_rhs,&w);
    2713:     PetscLogObjectParent((PetscObject)ksp,(PetscObject)w);
    2714:   }
    2715:   if (!tt) {
    2716:     VecDuplicate(ksp->vec_sol,&tt); flag = PETSC_TRUE;
    2717:     PetscLogObjectParent((PetscObject)ksp,(PetscObject)tt);
    2718:   }
    2719:   (*ksp->ops->buildresidual)(ksp,tt,w,V);
    2720:   if (flag) {VecDestroy(&tt);}
    2721:   return(0);
    2722: }

    2724: /*@
    2725:    KSPSetDiagonalScale - Tells KSP to symmetrically diagonally scale the system
    2726:      before solving. This actually CHANGES the matrix (and right hand side).

    2728:    Logically Collective on ksp

    2730:    Input Parameter:
    2731: +  ksp - the KSP context
    2732: -  scale - PETSC_TRUE or PETSC_FALSE

    2734:    Options Database Key:
    2735: +   -ksp_diagonal_scale -
    2736: -   -ksp_diagonal_scale_fix - scale the matrix back AFTER the solve

    2739:     Notes:
    2740:     Scales the matrix by  D^(-1/2)  A  D^(-1/2)  [D^(1/2) x ] = D^(-1/2) b
    2741:        where D_{ii} is 1/abs(A_{ii}) unless A_{ii} is zero and then it is 1.

    2743:     BE CAREFUL with this routine: it actually scales the matrix and right
    2744:     hand side that define the system. After the system is solved the matrix
    2745:     and right hand side remain scaled unless you use KSPSetDiagonalScaleFix()

    2747:     This should NOT be used within the SNES solves if you are using a line
    2748:     search.

    2750:     If you use this with the PCType Eisenstat preconditioner than you can
    2751:     use the PCEisenstatSetNoDiagonalScaling() option, or -pc_eisenstat_no_diagonal_scaling
    2752:     to save some unneeded, redundant flops.

    2754:    Level: intermediate

    2756: .seealso: KSPGetDiagonalScale(), KSPSetDiagonalScaleFix(), KSP
    2757: @*/
    2758: PetscErrorCode  KSPSetDiagonalScale(KSP ksp,PetscBool scale)
    2759: {
    2763:   ksp->dscale = scale;
    2764:   return(0);
    2765: }

    2767: /*@
    2768:    KSPGetDiagonalScale - Checks if KSP solver scales the matrix and
    2769:                           right hand side

    2771:    Not Collective

    2773:    Input Parameter:
    2774: .  ksp - the KSP context

    2776:    Output Parameter:
    2777: .  scale - PETSC_TRUE or PETSC_FALSE

    2779:    Notes:
    2780:     BE CAREFUL with this routine: it actually scales the matrix and right
    2781:     hand side that define the system. After the system is solved the matrix
    2782:     and right hand side remain scaled  unless you use KSPSetDiagonalScaleFix()

    2784:    Level: intermediate

    2786: .seealso: KSPSetDiagonalScale(), KSPSetDiagonalScaleFix(), KSP
    2787: @*/
    2788: PetscErrorCode  KSPGetDiagonalScale(KSP ksp,PetscBool  *scale)
    2789: {
    2793:   *scale = ksp->dscale;
    2794:   return(0);
    2795: }

    2797: /*@
    2798:    KSPSetDiagonalScaleFix - Tells KSP to diagonally scale the system
    2799:      back after solving.

    2801:    Logically Collective on ksp

    2803:    Input Parameter:
    2804: +  ksp - the KSP context
    2805: -  fix - PETSC_TRUE to scale back after the system solve, PETSC_FALSE to not
    2806:          rescale (default)

    2808:    Notes:
    2809:      Must be called after KSPSetDiagonalScale()

    2811:      Using this will slow things down, because it rescales the matrix before and
    2812:      after each linear solve. This is intended mainly for testing to allow one
    2813:      to easily get back the original system to make sure the solution computed is
    2814:      accurate enough.

    2816:    Level: intermediate

    2818: .seealso: KSPGetDiagonalScale(), KSPSetDiagonalScale(), KSPGetDiagonalScaleFix(), KSP
    2819: @*/
    2820: PetscErrorCode  KSPSetDiagonalScaleFix(KSP ksp,PetscBool fix)
    2821: {
    2825:   ksp->dscalefix = fix;
    2826:   return(0);
    2827: }

    2829: /*@
    2830:    KSPGetDiagonalScaleFix - Determines if KSP diagonally scales the system
    2831:      back after solving.

    2833:    Not Collective

    2835:    Input Parameter:
    2836: .  ksp - the KSP context

    2838:    Output Parameter:
    2839: .  fix - PETSC_TRUE to scale back after the system solve, PETSC_FALSE to not
    2840:          rescale (default)

    2842:    Notes:
    2843:      Must be called after KSPSetDiagonalScale()

    2845:      If PETSC_TRUE will slow things down, because it rescales the matrix before and
    2846:      after each linear solve. This is intended mainly for testing to allow one
    2847:      to easily get back the original system to make sure the solution computed is
    2848:      accurate enough.

    2850:    Level: intermediate

    2852: .seealso: KSPGetDiagonalScale(), KSPSetDiagonalScale(), KSPSetDiagonalScaleFix(), KSP
    2853: @*/
    2854: PetscErrorCode  KSPGetDiagonalScaleFix(KSP ksp,PetscBool  *fix)
    2855: {
    2859:   *fix = ksp->dscalefix;
    2860:   return(0);
    2861: }

    2863: /*@C
    2864:    KSPSetComputeOperators - set routine to compute the linear operators

    2866:    Logically Collective

    2868:    Input Arguments:
    2869: +  ksp - the KSP context
    2870: .  func - function to compute the operators
    2871: -  ctx - optional context

    2873:    Calling sequence of func:
    2874: $  func(KSP ksp,Mat A,Mat B,void *ctx)

    2876: +  ksp - the KSP context
    2877: .  A - the linear operator
    2878: .  B - preconditioning matrix
    2879: -  ctx - optional user-provided context

    2881:    Notes:
    2882:     The user provided func() will be called automatically at the very next call to KSPSolve(). It will not be called at future KSPSolve() calls
    2883:           unless either KSPSetComputeOperators() or KSPSetOperators() is called before that KSPSolve() is called.

    2885:           To reuse the same preconditioner for the next KSPSolve() and not compute a new one based on the most recently computed matrix call KSPSetReusePreconditioner()

    2887:    Level: beginner

    2889: .seealso: KSPSetOperators(), KSPSetComputeRHS(), DMKSPSetComputeOperators(), KSPSetComputeInitialGuess()
    2890: @*/
    2891: PetscErrorCode KSPSetComputeOperators(KSP ksp,PetscErrorCode (*func)(KSP,Mat,Mat,void*),void *ctx)
    2892: {
    2894:   DM             dm;

    2898:   KSPGetDM(ksp,&dm);
    2899:   DMKSPSetComputeOperators(dm,func,ctx);
    2900:   if (ksp->setupstage == KSP_SETUP_NEWRHS) ksp->setupstage = KSP_SETUP_NEWMATRIX;
    2901:   return(0);
    2902: }

    2904: /*@C
    2905:    KSPSetComputeRHS - set routine to compute the right hand side of the linear system

    2907:    Logically Collective

    2909:    Input Arguments:
    2910: +  ksp - the KSP context
    2911: .  func - function to compute the right hand side
    2912: -  ctx - optional context

    2914:    Calling sequence of func:
    2915: $  func(KSP ksp,Vec b,void *ctx)

    2917: +  ksp - the KSP context
    2918: .  b - right hand side of linear system
    2919: -  ctx - optional user-provided context

    2921:    Notes:
    2922:     The routine you provide will be called EACH you call KSPSolve() to prepare the new right hand side for that solve

    2924:    Level: beginner

    2926: .seealso: KSPSolve(), DMKSPSetComputeRHS(), KSPSetComputeOperators()
    2927: @*/
    2928: PetscErrorCode KSPSetComputeRHS(KSP ksp,PetscErrorCode (*func)(KSP,Vec,void*),void *ctx)
    2929: {
    2931:   DM             dm;

    2935:   KSPGetDM(ksp,&dm);
    2936:   DMKSPSetComputeRHS(dm,func,ctx);
    2937:   return(0);
    2938: }

    2940: /*@C
    2941:    KSPSetComputeInitialGuess - set routine to compute the initial guess of the linear system

    2943:    Logically Collective

    2945:    Input Arguments:
    2946: +  ksp - the KSP context
    2947: .  func - function to compute the initial guess
    2948: -  ctx - optional context

    2950:    Calling sequence of func:
    2951: $  func(KSP ksp,Vec x,void *ctx)

    2953: +  ksp - the KSP context
    2954: .  x - solution vector
    2955: -  ctx - optional user-provided context

    2957:    Notes: This should only be used in conjunction with KSPSetComputeRHS(), KSPSetComputeOperators(), otherwise
    2958:    call KSPSetInitialGuessNonzero() and set the initial guess values in the solution vector passed to KSPSolve().

    2960:    Level: beginner

    2962: .seealso: KSPSolve(), KSPSetComputeRHS(), KSPSetComputeOperators(), DMKSPSetComputeInitialGuess()
    2963: @*/
    2964: PetscErrorCode KSPSetComputeInitialGuess(KSP ksp,PetscErrorCode (*func)(KSP,Vec,void*),void *ctx)
    2965: {
    2967:   DM             dm;

    2971:   KSPGetDM(ksp,&dm);
    2972:   DMKSPSetComputeInitialGuess(dm,func,ctx);
    2973:   return(0);
    2974: }

    2976: /*@
    2977:    KSPSetUseExplicitTranspose - Determines if transpose the system explicitly
    2978:    in KSPSolveTranspose.

    2980:    Logically Collective on ksp

    2982:    Input Parameter:
    2983: .  ksp - the KSP context

    2985:    Output Parameter:
    2986: .  flg - PETSC_TRUE to transpose the system in KSPSolveTranspose, PETSC_FALSE to not
    2987:          transpose (default)

    2989:    Level: advanced

    2991: .seealso: KSPSolveTranspose(), KSP
    2992: @*/
    2993: PetscErrorCode KSPSetUseExplicitTranspose(KSP ksp,PetscBool flg)
    2994: {
    2997:   ksp->transpose.use_explicittranspose = flg;
    2998:   return(0);
    2999: }