Actual source code: wp.c

petsc-master 2019-09-20
Report Typos and Errors

  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: }