Date: 2015-09-03T15:05:17+00:00

Actual source code: svdopts.c
slepc-3.6.1 2015-09-03
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      1: /*
      2:      SVD routines for setting solver options.

      4:    - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
      5:    SLEPc - Scalable Library for Eigenvalue Problem Computations
      6:    Copyright (c) 2002-2015, Universitat Politecnica de Valencia, Spain

      8:    This file is part of SLEPc.

     10:    SLEPc is free software: you can redistribute it and/or modify it under  the
     11:    terms of version 3 of the GNU Lesser General Public License as published by
     12:    the Free Software Foundation.

     14:    SLEPc  is  distributed in the hope that it will be useful, but WITHOUT  ANY
     15:    WARRANTY;  without even the implied warranty of MERCHANTABILITY or  FITNESS
     16:    FOR  A  PARTICULAR PURPOSE. See the GNU Lesser General Public  License  for
     17:    more details.

     19:    You  should have received a copy of the GNU Lesser General  Public  License
     20:    along with SLEPc. If not, see <http://www.gnu.org/licenses/>.
     21:    - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
     22: */

     24: #include <slepc/private/svdimpl.h>      /*I "slepcsvd.h" I*/

     28: /*@
     29:    SVDSetImplicitTranspose - Indicates how to handle the transpose of the matrix
     30:    associated with the singular value problem.

     32:    Logically Collective on SVD

     34:    Input Parameters:
     35: +  svd  - the singular value solver context
     36: -  impl - how to handle the transpose (implicitly or not)

     38:    Options Database Key:
     39: .  -svd_implicittranspose - Activate the implicit transpose mode.

     41:    Notes:
     42:    By default, the transpose of the matrix is explicitly built (if the matrix
     43:    has defined the MatTranspose operation).

     45:    If this flag is set to true, the solver does not build the transpose, but
     46:    handles it implicitly via MatMultTranspose() (or MatMultHermitianTranspose()
     47:    in the complex case) operations. This is likely to be more inefficient
     48:    than the default behaviour, both in sequential and in parallel, but
     49:    requires less storage.

     51:    Level: advanced

     53: .seealso: SVDGetImplicitTranspose(), SVDSolve(), SVDSetOperator()
     54: @*/
     55: PetscErrorCode SVDSetImplicitTranspose(SVD svd,PetscBool impl)
     56: {
     60:   if (svd->impltrans!=impl) {
     61:     svd->impltrans = impl;
     62:     svd->state     = SVD_STATE_INITIAL;
     63:   }
     64:   return(0);
     65: }

     69: /*@
     70:    SVDGetImplicitTranspose - Gets the mode used to handle the transpose
     71:    of the matrix associated with the singular value problem.

     73:    Not Collective

     75:    Input Parameter:
     76: .  svd  - the singular value solver context

     78:    Output paramter:
     79: .  impl - how to handle the transpose (implicitly or not)

     81:    Level: advanced

     83: .seealso: SVDSetImplicitTranspose(), SVDSolve(), SVDSetOperator()
     84: @*/
     85: PetscErrorCode SVDGetImplicitTranspose(SVD svd,PetscBool *impl)
     86: {
     90:   *impl = svd->impltrans;
     91:   return(0);
     92: }

     96: /*@
     97:    SVDSetTolerances - Sets the tolerance and maximum
     98:    iteration count used by the default SVD convergence testers.

    100:    Logically Collective on SVD

    102:    Input Parameters:
    103: +  svd - the singular value solver context
    104: .  tol - the convergence tolerance
    105: -  maxits - maximum number of iterations to use

    107:    Options Database Keys:
    108: +  -svd_tol <tol> - Sets the convergence tolerance
    109: -  -svd_max_it <maxits> - Sets the maximum number of iterations allowed
    110:    (use PETSC_DECIDE to compute an educated guess based on basis and matrix sizes)

    112:    Note:
    113:    Use PETSC_DEFAULT for either argument to assign a reasonably good value.

    115:    Level: intermediate

    117: .seealso: SVDGetTolerances()
    118: @*/
    119: PetscErrorCode SVDSetTolerances(SVD svd,PetscReal tol,PetscInt maxits)
    120: {
    125:   if (tol == PETSC_DEFAULT) {
    126:     svd->tol   = PETSC_DEFAULT;
    127:     svd->state = SVD_STATE_INITIAL;
    128:   } else {
    129:     if (tol <= 0.0) SETERRQ(PetscObjectComm((PetscObject)svd),PETSC_ERR_ARG_OUTOFRANGE,"Illegal value of tol. Must be > 0");
    130:     svd->tol = tol;
    131:   }
    132:   if (maxits == PETSC_DEFAULT || maxits == PETSC_DECIDE) {
    133:     svd->max_it = 0;
    134:     svd->state  = SVD_STATE_INITIAL;
    135:   } else {
    136:     if (maxits <= 0) SETERRQ(PetscObjectComm((PetscObject)svd),PETSC_ERR_ARG_OUTOFRANGE,"Illegal value of maxits. Must be > 0");
    137:     svd->max_it = maxits;
    138:   }
    139:   return(0);
    140: }

    144: /*@
    145:    SVDGetTolerances - Gets the tolerance and maximum
    146:    iteration count used by the default SVD convergence tests.

    148:    Not Collective

    150:    Input Parameter:
    151: .  svd - the singular value solver context

    153:    Output Parameters:
    154: +  tol - the convergence tolerance
    155: -  maxits - maximum number of iterations

    157:    Notes:
    158:    The user can specify NULL for any parameter that is not needed.

    160:    Level: intermediate

    162: .seealso: SVDSetTolerances()
    163: @*/
    164: PetscErrorCode SVDGetTolerances(SVD svd,PetscReal *tol,PetscInt *maxits)
    165: {
    168:   if (tol)    *tol    = svd->tol;
    169:   if (maxits) *maxits = svd->max_it;
    170:   return(0);
    171: }

    175: /*@
    176:    SVDSetDimensions - Sets the number of singular values to compute
    177:    and the dimension of the subspace.

    179:    Logically Collective on SVD

    181:    Input Parameters:
    182: +  svd - the singular value solver context
    183: .  nsv - number of singular values to compute
    184: .  ncv - the maximum dimension of the subspace to be used by the solver
    185: -  mpd - the maximum dimension allowed for the projected problem

    187:    Options Database Keys:
    188: +  -svd_nsv <nsv> - Sets the number of singular values
    189: .  -svd_ncv <ncv> - Sets the dimension of the subspace
    190: -  -svd_mpd <mpd> - Sets the maximum projected dimension

    192:    Notes:
    193:    Use PETSC_DEFAULT for ncv and mpd to assign a reasonably good value, which is
    194:    dependent on the solution method and the number of singular values required.

    196:    The parameters ncv and mpd are intimately related, so that the user is advised
    197:    to set one of them at most. Normal usage is that
    198:    (a) in cases where nsv is small, the user sets ncv (a reasonable default is 2*nsv); and
    199:    (b) in cases where nsv is large, the user sets mpd.

    201:    The value of ncv should always be between nsv and (nsv+mpd), typically
    202:    ncv=nsv+mpd. If nev is not too large, mpd=nsv is a reasonable choice, otherwise
    203:    a smaller value should be used.

    205:    Level: intermediate

    207: .seealso: SVDGetDimensions()
    208: @*/
    209: PetscErrorCode SVDSetDimensions(SVD svd,PetscInt nsv,PetscInt ncv,PetscInt mpd)
    210: {
    216:   if (nsv<1) SETERRQ(PetscObjectComm((PetscObject)svd),PETSC_ERR_ARG_OUTOFRANGE,"Illegal value of nsv. Must be > 0");
    217:   svd->nsv = nsv;
    218:   if (ncv == PETSC_DEFAULT || ncv == PETSC_DECIDE) {
    219:     svd->ncv = 0;
    220:   } else {
    221:     if (ncv<1) SETERRQ(PetscObjectComm((PetscObject)svd),PETSC_ERR_ARG_OUTOFRANGE,"Illegal value of ncv. Must be > 0");
    222:     svd->ncv = ncv;
    223:   }
    224:   if (mpd == PETSC_DECIDE || mpd == PETSC_DEFAULT) {
    225:     svd->mpd = 0;
    226:   } else {
    227:     if (mpd<1) SETERRQ(PetscObjectComm((PetscObject)svd),PETSC_ERR_ARG_OUTOFRANGE,"Illegal value of mpd. Must be > 0");
    228:     svd->mpd = mpd;
    229:   }
    230:   svd->state = SVD_STATE_INITIAL;
    231:   return(0);
    232: }

    236: /*@
    237:    SVDGetDimensions - Gets the number of singular values to compute
    238:    and the dimension of the subspace.

    240:    Not Collective

    242:    Input Parameter:
    243: .  svd - the singular value context

    245:    Output Parameters:
    246: +  nsv - number of singular values to compute
    247: .  ncv - the maximum dimension of the subspace to be used by the solver
    248: -  mpd - the maximum dimension allowed for the projected problem

    250:    Notes:
    251:    The user can specify NULL for any parameter that is not needed.

    253:    Level: intermediate

    255: .seealso: SVDSetDimensions()
    256: @*/
    257: PetscErrorCode SVDGetDimensions(SVD svd,PetscInt *nsv,PetscInt *ncv,PetscInt *mpd)
    258: {
    261:   if (nsv) *nsv = svd->nsv;
    262:   if (ncv) *ncv = svd->ncv;
    263:   if (mpd) *mpd = svd->mpd;
    264:   return(0);
    265: }

    269: /*@
    270:     SVDSetWhichSingularTriplets - Specifies which singular triplets are
    271:     to be sought.

    273:     Logically Collective on SVD

    275:     Input Parameter:
    276: .   svd - singular value solver context obtained from SVDCreate()

    278:     Output Parameter:
    279: .   which - which singular triplets are to be sought

    281:     Possible values:
    282:     The parameter 'which' can have one of these values:

    284: +     SVD_LARGEST  - largest singular values
    285: -     SVD_SMALLEST - smallest singular values

    287:     Options Database Keys:
    288: +   -svd_largest  - Sets largest singular values
    289: -   -svd_smallest - Sets smallest singular values

    291:     Level: intermediate

    293: .seealso: SVDGetWhichSingularTriplets(), SVDWhich
    294: @*/
    295: PetscErrorCode SVDSetWhichSingularTriplets(SVD svd,SVDWhich which)
    296: {
    300:   switch (which) {
    301:     case SVD_LARGEST:
    302:     case SVD_SMALLEST:
    303:       if (svd->which != which) {
    304:         svd->state = SVD_STATE_INITIAL;
    305:         svd->which = which;
    306:       }
    307:       break;
    308:   default:
    309:     SETERRQ(PetscObjectComm((PetscObject)svd),PETSC_ERR_ARG_OUTOFRANGE,"Invalid 'which' parameter");
    310:   }
    311:   return(0);
    312: }

    316: /*@
    317:     SVDGetWhichSingularTriplets - Returns which singular triplets are
    318:     to be sought.

    320:     Not Collective

    322:     Input Parameter:
    323: .   svd - singular value solver context obtained from SVDCreate()

    325:     Output Parameter:
    326: .   which - which singular triplets are to be sought

    328:     Notes:
    329:     See SVDSetWhichSingularTriplets() for possible values of which

    331:     Level: intermediate

    333: .seealso: SVDSetWhichSingularTriplets(), SVDWhich
    334: @*/
    335: PetscErrorCode SVDGetWhichSingularTriplets(SVD svd,SVDWhich *which)
    336: {
    340:   *which = svd->which;
    341:   return(0);
    342: }

    346: /*@
    347:    SVDSetFromOptions - Sets SVD options from the options database.
    348:    This routine must be called before SVDSetUp() if the user is to be
    349:    allowed to set the solver type.

    351:    Collective on SVD

    353:    Input Parameters:
    354: .  svd - the singular value solver context

    356:    Notes:
    357:    To see all options, run your program with the -help option.

    359:    Level: beginner

    361: .seealso:
    362: @*/
    363: PetscErrorCode SVDSetFromOptions(SVD svd)
    364: {
    365:   PetscErrorCode   ierr;
    366:   char             type[256],monfilename[PETSC_MAX_PATH_LEN];
    367:   PetscBool        flg,val,flg1,flg2,flg3;
    368:   PetscInt         i,j,k;
    369:   PetscReal        r;
    370:   PetscViewer      monviewer;
    371:   SlepcConvMonitor ctx;

    375:   SVDRegisterAll();
    376:   PetscObjectOptionsBegin((PetscObject)svd);
    377:     PetscOptionsFList("-svd_type","Singular Value Solver method","SVDSetType",SVDList,(char*)(((PetscObject)svd)->type_name?((PetscObject)svd)->type_name:SVDCROSS),type,256,&flg);
    378:     if (flg) {
    379:       SVDSetType(svd,type);
    380:     } else if (!((PetscObject)svd)->type_name) {
    381:       SVDSetType(svd,SVDCROSS);
    382:     }

    384:     PetscOptionsName("-svd_view","Print detailed information on solver used","SVDView",&flg);
    385:     PetscOptionsName("-svd_view_vectors","View computed singular vectors","SVDVectorsView",0);
    386:     PetscOptionsName("-svd_view_values","View computed singular values","SVDValuesView",0);
    387:     PetscOptionsName("-svd_converged_reason","Print reason for convergence, and number of iterations","SVDReasonView",0);
    388:     PetscOptionsName("-svd_error_absolute","Print absolute errors of each singular triplet","SVDErrorView",0);
    389:     PetscOptionsName("-svd_error_relative","Print relative errors of each singular triplet","SVDErrorView",0);

    391:     PetscOptionsBool("-svd_implicittranspose","Handle matrix transpose implicitly","SVDSetImplicitTranspose",svd->impltrans,&val,&flg);
    392:     if (flg) {
    393:       SVDSetImplicitTranspose(svd,val);
    394:     }

    396:     i = svd->max_it? svd->max_it: PETSC_DEFAULT;
    397:     PetscOptionsInt("-svd_max_it","Maximum number of iterations","SVDSetTolerances",svd->max_it,&i,&flg1);
    398:     r = svd->tol;
    399:     PetscOptionsReal("-svd_tol","Tolerance","SVDSetTolerances",svd->tol==PETSC_DEFAULT?SLEPC_DEFAULT_TOL:svd->tol,&r,&flg2);
    400:     if (flg1 || flg2) {
    401:       SVDSetTolerances(svd,r,i);
    402:     }

    404:     i = svd->nsv;
    405:     PetscOptionsInt("-svd_nsv","Number of singular values to compute","SVDSetDimensions",svd->nsv,&i,&flg1);
    406:     j = svd->ncv? svd->ncv: PETSC_DEFAULT;
    407:     PetscOptionsInt("-svd_ncv","Number of basis vectors","SVDSetDimensions",svd->ncv,&j,&flg2);
    408:     k = svd->mpd? svd->mpd: PETSC_DEFAULT;
    409:     PetscOptionsInt("-svd_mpd","Maximum dimension of projected problem","SVDSetDimensions",svd->mpd,&k,&flg3);
    410:     if (flg1 || flg2 || flg3) {
    411:       SVDSetDimensions(svd,i,j,k);
    412:     }

    414:     PetscOptionsBoolGroupBegin("-svd_largest","compute largest singular values","SVDSetWhichSingularTriplets",&flg);
    415:     if (flg) { SVDSetWhichSingularTriplets(svd,SVD_LARGEST); }
    416:     PetscOptionsBoolGroupEnd("-svd_smallest","compute smallest singular values","SVDSetWhichSingularTriplets",&flg);
    417:     if (flg) { SVDSetWhichSingularTriplets(svd,SVD_SMALLEST); }

    419:     /* -----------------------------------------------------------------------*/
    420:     /*
    421:       Cancels all monitors hardwired into code before call to SVDSetFromOptions()
    422:     */
    423:     flg = PETSC_FALSE;
    424:     PetscOptionsBool("-svd_monitor_cancel","Remove any hardwired monitor routines","SVDMonitorCancel",flg,&flg,NULL);
    425:     if (flg) {
    426:       SVDMonitorCancel(svd);
    427:     }

    429:     PetscOptionsString("-svd_monitor_all","Monitor approximate singular values and error estimates","SVDMonitorSet","stdout",monfilename,PETSC_MAX_PATH_LEN,&flg);
    430:     if (flg) {
    431:       PetscViewerASCIIOpen(PetscObjectComm((PetscObject)svd),monfilename,&monviewer);
    432:       SVDMonitorSet(svd,SVDMonitorAll,monviewer,(PetscErrorCode (*)(void**))PetscViewerDestroy);
    433:       SVDSetTrackAll(svd,PETSC_TRUE);
    434:     }
    435:     PetscOptionsString("-svd_monitor_conv","Monitor approximate singular values and error estimates as they converge","SVDMonitorSet","stdout",monfilename,PETSC_MAX_PATH_LEN,&flg);
    436:     if (flg) {
    437:         PetscNew(&ctx);
    438:         PetscViewerASCIIOpen(PetscObjectComm((PetscObject)svd),monfilename,&ctx->viewer);
    439:         SVDMonitorSet(svd,SVDMonitorConverged,ctx,(PetscErrorCode (*)(void**))SlepcConvMonitorDestroy);
    440:     }
    441:     PetscOptionsString("-svd_monitor","Monitor first unconverged approximate singular value and error estimate","SVDMonitorSet","stdout",monfilename,PETSC_MAX_PATH_LEN,&flg);
    442:     if (flg) {
    443:       PetscViewerASCIIOpen(PetscObjectComm((PetscObject)svd),monfilename,&monviewer);
    444:       SVDMonitorSet(svd,SVDMonitorFirst,monviewer,(PetscErrorCode (*)(void**))PetscViewerDestroy);
    445:     }
    446:     flg = PETSC_FALSE;
    447:     PetscOptionsBool("-svd_monitor_lg","Monitor first unconverged approximate singular value and error estimate graphically","SVDMonitorSet",flg,&flg,NULL);
    448:     if (flg) {
    449:       SVDMonitorSet(svd,SVDMonitorLG,NULL,NULL);
    450:     }
    451:     flg = PETSC_FALSE;
    452:     PetscOptionsBool("-svd_monitor_lg_all","Monitor error estimates graphically","SVDMonitorSet",flg,&flg,NULL);
    453:     if (flg) {
    454:       SVDMonitorSet(svd,SVDMonitorLGAll,NULL,NULL);
    455:       SVDSetTrackAll(svd,PETSC_TRUE);
    456:     }

    458:     if (svd->ops->setfromoptions) {
    459:       (*svd->ops->setfromoptions)(PetscOptionsObject,svd);
    460:     }
    461:     PetscObjectProcessOptionsHandlers((PetscObject)svd);
    462:   PetscOptionsEnd();

    464:   if (!svd->V) { SVDGetBV(svd,&svd->V,&svd->U); }
    465:   BVSetFromOptions(svd->V);
    466:   BVSetFromOptions(svd->U);
    467:   if (!svd->ds) { SVDGetDS(svd,&svd->ds); }
    468:   DSSetFromOptions(svd->ds);
    469:   PetscRandomSetFromOptions(svd->rand);
    470:   return(0);
    471: }

    475: /*@
    476:    SVDSetTrackAll - Specifies if the solver must compute the residual norm of all
    477:    approximate singular value or not.

    479:    Logically Collective on SVD

    481:    Input Parameters:
    482: +  svd      - the singular value solver context
    483: -  trackall - whether to compute all residuals or not

    485:    Notes:
    486:    If the user sets trackall=PETSC_TRUE then the solver computes (or estimates)
    487:    the residual norm for each singular value approximation. Computing the residual is
    488:    usually an expensive operation and solvers commonly compute only the residual
    489:    associated to the first unconverged singular value.

    491:    The options '-svd_monitor_all' and '-svd_monitor_lg_all' automatically
    492:    activate this option.

    494:    Level: developer

    496: .seealso: SVDGetTrackAll()
    497: @*/
    498: PetscErrorCode SVDSetTrackAll(SVD svd,PetscBool trackall)
    499: {
    503:   svd->trackall = trackall;
    504:   return(0);
    505: }

    509: /*@
    510:    SVDGetTrackAll - Returns the flag indicating whether all residual norms must
    511:    be computed or not.

    513:    Not Collective

    515:    Input Parameter:
    516: .  svd - the singular value solver context

    518:    Output Parameter:
    519: .  trackall - the returned flag

    521:    Level: developer

    523: .seealso: SVDSetTrackAll()
    524: @*/
    525: PetscErrorCode SVDGetTrackAll(SVD svd,PetscBool *trackall)
    526: {
    530:   *trackall = svd->trackall;
    531:   return(0);
    532: }

    537: /*@C
    538:    SVDSetOptionsPrefix - Sets the prefix used for searching for all
    539:    SVD options in the database.

    541:    Logically Collective on SVD

    543:    Input Parameters:
    544: +  svd - the singular value solver context
    545: -  prefix - the prefix string to prepend to all SVD option requests

    547:    Notes:
    548:    A hyphen (-) must NOT be given at the beginning of the prefix name.
    549:    The first character of all runtime options is AUTOMATICALLY the
    550:    hyphen.

    552:    For example, to distinguish between the runtime options for two
    553:    different SVD contexts, one could call
    554: .vb
    555:       SVDSetOptionsPrefix(svd1,"svd1_")
    556:       SVDSetOptionsPrefix(svd2,"svd2_")
    557: .ve

    559:    Level: advanced

    561: .seealso: SVDAppendOptionsPrefix(), SVDGetOptionsPrefix()
    562: @*/
    563: PetscErrorCode SVDSetOptionsPrefix(SVD svd,const char *prefix)
    564: {
    566:   PetscBool      flg1,flg2;
    567:   EPS            eps;

    571:   if (!svd->V) { SVDGetBV(svd,&svd->V,&svd->U); }
    572:   BVSetOptionsPrefix(svd->V,prefix);
    573:   BVSetOptionsPrefix(svd->U,prefix);
    574:   if (!svd->ds) { SVDGetDS(svd,&svd->ds); }
    575:   DSSetOptionsPrefix(svd->ds,prefix);
    576:   PetscObjectSetOptionsPrefix((PetscObject)svd,prefix);
    577:   PetscObjectTypeCompare((PetscObject)svd,SVDCROSS,&flg1);
    578:   PetscObjectTypeCompare((PetscObject)svd,SVDCYCLIC,&flg2);
    579:   if (flg1) {
    580:     SVDCrossGetEPS(svd,&eps);
    581:   } else if (flg2) {
    582:       SVDCyclicGetEPS(svd,&eps);
    583:   }
    584:   if (flg1 || flg2) {
    585:     EPSSetOptionsPrefix(eps,prefix);
    586:     EPSAppendOptionsPrefix(eps,"svd_");
    587:   }
    588:   return(0);
    589: }

    593: /*@C
    594:    SVDAppendOptionsPrefix - Appends to the prefix used for searching for all
    595:    SVD options in the database.

    597:    Logically Collective on SVD

    599:    Input Parameters:
    600: +  svd - the singular value solver context
    601: -  prefix - the prefix string to prepend to all SVD option requests

    603:    Notes:
    604:    A hyphen (-) must NOT be given at the beginning of the prefix name.
    605:    The first character of all runtime options is AUTOMATICALLY the hyphen.

    607:    Level: advanced

    609: .seealso: SVDSetOptionsPrefix(), SVDGetOptionsPrefix()
    610: @*/
    611: PetscErrorCode SVDAppendOptionsPrefix(SVD svd,const char *prefix)
    612: {
    614:   PetscBool      flg1,flg2;
    615:   EPS            eps;

    619:   if (!svd->V) { SVDGetBV(svd,&svd->V,&svd->U); }
    620:   BVSetOptionsPrefix(svd->V,prefix);
    621:   BVSetOptionsPrefix(svd->U,prefix);
    622:   if (!svd->ds) { SVDGetDS(svd,&svd->ds); }
    623:   DSSetOptionsPrefix(svd->ds,prefix);
    624:   PetscObjectAppendOptionsPrefix((PetscObject)svd,prefix);
    625:   PetscObjectTypeCompare((PetscObject)svd,SVDCROSS,&flg1);
    626:   PetscObjectTypeCompare((PetscObject)svd,SVDCYCLIC,&flg2);
    627:   if (flg1) {
    628:     SVDCrossGetEPS(svd,&eps);
    629:   } else if (flg2) {
    630:     SVDCyclicGetEPS(svd,&eps);
    631:   }
    632:   if (flg1 || flg2) {
    633:     EPSSetOptionsPrefix(eps,((PetscObject)svd)->prefix);
    634:     EPSAppendOptionsPrefix(eps,"svd_");
    635:   }
    636:   return(0);
    637: }

    641: /*@C
    642:    SVDGetOptionsPrefix - Gets the prefix used for searching for all
    643:    SVD options in the database.

    645:    Not Collective

    647:    Input Parameters:
    648: .  svd - the singular value solver context

    650:    Output Parameters:
    651: .  prefix - pointer to the prefix string used is returned

    653:    Notes: On the fortran side, the user should pass in a string 'prefix' of
    654:    sufficient length to hold the prefix.

    656:    Level: advanced

    658: .seealso: SVDSetOptionsPrefix(), SVDAppendOptionsPrefix()
    659: @*/
    660: PetscErrorCode SVDGetOptionsPrefix(SVD svd,const char *prefix[])
    661: {

    667:   PetscObjectGetOptionsPrefix((PetscObject)svd,prefix);
    668:   return(0);
    669: }