Actual source code: wp.c
petsc-3.10.5 2019-03-28
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      2: /*MC
      3:      MATMFFD_WP - Implements an alternative approach for computing the differencing parameter
      4:         h used with the finite difference based matrix-free Jacobian.  This code
      5:         implements the strategy of M. Pernice and H. Walker:

      7:       h = error_rel * sqrt(1 + ||U||) / ||a||

      9:       Notes:
     10:         1) || U || does not change between linear iterations so is reused
     11:         2) In GMRES || a || == 1 and so does not need to ever be computed except at restart
     12:            when it is recomputed.

     14:       Reference:  M. Pernice and H. F. Walker, "NITSOL: A Newton Iterative
     15:       Solver for Nonlinear Systems", SIAM J. Sci. Stat. Comput.", 1998,
     16:       vol 19, pp. 302--318.

     18:    Options Database Keys:
     19: .   -mat_mffd_compute_normu -Compute the norm of u everytime see MatMFFDWPSetComputeNormU()

     22:    Level: intermediate

     24:    Notes:
     25:     Requires no global collectives when used with GMRES

     27:    Formula used:
     28:      F'(u)*a = [F(u+h*a) - F(u)]/h where

     30: .seealso: MATMFFD, MatCreateMFFD(), MatCreateSNESMF(), MATMFFD_DS

     32: M*/

     34: /*
     35:     This include file defines the data structure  MatMFFD that
     36:    includes information about the computation of h. It is shared by
     37:    all implementations that people provide.

     39:    See snesmfjdef.c for  a full set of comments on the routines below.
     40: */
     41:  #include <petsc/private/matimpl.h>
     42:  #include <../src/mat/impls/mffd/mffdimpl.h>

     44: typedef struct {
     45:   PetscReal normUfact;                    /* previous sqrt(1.0 + || U ||) */
     46:   PetscBool computenormU;
     47: } MatMFFD_WP;

     49: /*
     50:      MatMFFDCompute_WP - Standard PETSc code for
     51:    computing h with matrix-free finite differences.

     53:   Input Parameters:
     54: +   ctx - the matrix free context
     55: .   U - the location at which you want the Jacobian
     56: -   a - the direction you want the derivative

     58:   Output Parameter:
     59: .   h - the scale computed

     61: */
     62: static PetscErrorCode MatMFFDCompute_WP(MatMFFD ctx,Vec U,Vec a,PetscScalar *h,PetscBool  *zeroa)
     63: {
     64:   MatMFFD_WP     *hctx = (MatMFFD_WP*)ctx->hctx;
     65:   PetscReal      normU,norma;

     69:   if (!(ctx->count % ctx->recomputeperiod)) {
     70:     if (hctx->computenormU || !ctx->ncurrenth) {
     71:       VecNorm(U,NORM_2,&normU);
     72:       hctx->normUfact = PetscSqrtReal(1.0+normU);
     73:     }
     74:     VecNorm(a,NORM_2,&norma);
     75:     if (norma == 0.0) {
     76:       *zeroa = PETSC_TRUE;
     77:       return(0);
     78:     }
     79:     *zeroa = PETSC_FALSE;
     80:     *h     = ctx->error_rel*hctx->normUfact/norma;
     81:   } else {
     82:     *h = ctx->currenth;
     83:   }
     84:   return(0);
     85: }

     87: /*
     88:    MatMFFDView_WP - Prints information about this particular
     89:      method for computing h. Note that this does not print the general
     90:      information about the matrix free, that is printed by the calling
     91:      routine.

     93:   Input Parameters:
     94: +   ctx - the matrix free context
     95: -   viewer - the PETSc viewer

     97: */
     98: static PetscErrorCode MatMFFDView_WP(MatMFFD ctx,PetscViewer viewer)
     99: {
    100:   MatMFFD_WP     *hctx = (MatMFFD_WP*)ctx->hctx;
    102:   PetscBool      iascii;

    105:   PetscObjectTypeCompare((PetscObject)viewer,PETSCVIEWERASCII,&iascii);
    106:   if (iascii) {
    107:     if (hctx->computenormU) {
    108:        PetscViewerASCIIPrintf(viewer,"    Computes normU\n");
    109:     } else {
    110:        PetscViewerASCIIPrintf(viewer,"    Does not compute normU\n");
    111:     }
    112:   }
    113:   return(0);
    114: }

    116: /*
    117:    MatMFFDSetFromOptions_WP - Looks in the options database for
    118:      any options appropriate for this method

    120:   Input Parameter:
    121: .  ctx - the matrix free context

    123: */
    124: static PetscErrorCode MatMFFDSetFromOptions_WP(PetscOptionItems *PetscOptionsObject,MatMFFD ctx)
    125: {
    127:   MatMFFD_WP     *hctx = (MatMFFD_WP*)ctx->hctx;

    130:   PetscOptionsHead(PetscOptionsObject,"Walker-Pernice options");
    131:   PetscOptionsBool("-mat_mffd_compute_normu","Compute the norm of u","MatMFFDWPSetComputeNormU", hctx->computenormU,&hctx->computenormU,NULL);
    132:   PetscOptionsTail();
    133:   return(0);
    134: }

    136: /*
    137:    MatMFFDDestroy_WP - Frees the space allocated by
    138:        MatCreateMFFD_WP().

    140:   Input Parameter:
    141: .  ctx - the matrix free context

    143:    Notes:
    144:     does not free the ctx, that is handled by the calling routine

    146: */
    147: static PetscErrorCode MatMFFDDestroy_WP(MatMFFD ctx)
    148: {

    152:   PetscFree(ctx->hctx);
    153:   return(0);
    154: }

    156: PetscErrorCode  MatMFFDWPSetComputeNormU_P(Mat mat,PetscBool flag)
    157: {
    158:   MatMFFD    ctx   = (MatMFFD)mat->data;
    159:   MatMFFD_WP *hctx = (MatMFFD_WP*)ctx->hctx;

    162:   hctx->computenormU = flag;
    163:   return(0);
    164: }

    166: /*@
    167:     MatMFFDWPSetComputeNormU - Sets whether it computes the ||U|| used by the WP
    168:              PETSc routine for computing h. With any Krylov solver this need only
    169:              be computed during the first iteration and kept for later.

    171:   Input Parameters:
    172: +   A - the matrix created with MatCreateSNESMF()
    173: -   flag - PETSC_TRUE causes it to compute ||U||, PETSC_FALSE uses the previous value

    175:   Options Database Key:
    176: .   -mat_mffd_compute_normu <true,false> - true by default, false can save calculations but you
    177:               must be sure that ||U|| has not changed in the mean time.

    179:   Level: advanced

    181:   Notes:
    182:    See the manual page for MATMFFD_WP for a complete description of the
    183:    algorithm used to compute h.

    185: .seealso: MatMFFDSetFunctionError(), MatCreateSNESMF()

    187: @*/
    188: PetscErrorCode  MatMFFDWPSetComputeNormU(Mat A,PetscBool flag)
    189: {

    194:   PetscTryMethod(A,"MatMFFDWPSetComputeNormU_C",(Mat,PetscBool),(A,flag));
    195:   return(0);
    196: }

    198: /*
    199:      MatCreateMFFD_WP - Standard PETSc code for
    200:    computing h with matrix-free finite differences.

    202:    Input Parameter:
    203: .  ctx - the matrix free context created by MatCreateMFFD()

    205: */
    206: PETSC_EXTERN PetscErrorCode MatCreateMFFD_WP(MatMFFD ctx)
    207: {
    209:   MatMFFD_WP     *hctx;

    212:   /* allocate my own private data structure */
    213:   PetscNewLog(ctx,&hctx);
    214:   ctx->hctx          = (void*)hctx;
    215:   hctx->computenormU = PETSC_FALSE;

    217:   /* set the functions I am providing */
    218:   ctx->ops->compute        = MatMFFDCompute_WP;
    219:   ctx->ops->destroy        = MatMFFDDestroy_WP;
    220:   ctx->ops->view           = MatMFFDView_WP;
    221:   ctx->ops->setfromoptions = MatMFFDSetFromOptions_WP;

    223:   PetscObjectComposeFunction((PetscObject)ctx->mat,"MatMFFDWPSetComputeNormU_C",MatMFFDWPSetComputeNormU_P);
    224:   return(0);
    225: }