Actual source code: linesearchbasic.c
petsc-3.10.5 2019-03-28
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      1:  #include <petsc/private/linesearchimpl.h>
      2:  #include <petsc/private/snesimpl.h>

      4: static PetscErrorCode  SNESLineSearchApply_Basic(SNESLineSearch linesearch)
      5: {
      6:   PetscBool      changed_y, changed_w;
      8:   Vec            X, F, Y, W;
      9:   SNES           snes;
     10:   PetscReal      gnorm, xnorm, ynorm, lambda;
     11:   PetscBool      domainerror;

     14:   SNESLineSearchGetVecs(linesearch, &X, &F, &Y, &W, NULL);
     15:   SNESLineSearchGetNorms(linesearch, &xnorm, &gnorm, &ynorm);
     16:   SNESLineSearchGetLambda(linesearch, &lambda);
     17:   SNESLineSearchGetSNES(linesearch, &snes);
     18:   SNESLineSearchSetReason(linesearch, SNES_LINESEARCH_SUCCEEDED);

     20:   /* precheck */
     21:   SNESLineSearchPreCheck(linesearch,X,Y,&changed_y);

     23:   /* update */
     24:   VecWAXPY(W,-lambda,Y,X);
     25:   if (linesearch->ops->viproject) {
     26:     (*linesearch->ops->viproject)(snes, W);
     27:   }

     29:   /* postcheck */
     30:   SNESLineSearchPostCheck(linesearch,X,Y,W,&changed_y,&changed_w);
     31:   if (changed_y) {
     32:     VecWAXPY(W,-lambda,Y,X);
     33:     if (linesearch->ops->viproject) {
     34:       (*linesearch->ops->viproject)(snes, W);
     35:     }
     36:   }
     37:   if (linesearch->norms || snes->iter < snes->max_its-1) {
     38:     (*linesearch->ops->snesfunc)(snes,W,F);
     39:     SNESGetFunctionDomainError(snes, &domainerror);
     40:     if (domainerror) {
     41:       SNESLineSearchSetReason(linesearch, SNES_LINESEARCH_FAILED_DOMAIN);
     42:       return(0);
     43:     }
     44:   }

     46:   if (linesearch->norms) {
     47:     if (!linesearch->ops->vinorm) {VecNormBegin(F, NORM_2, &linesearch->fnorm);}
     48:     VecNormBegin(Y, NORM_2, &linesearch->ynorm);
     49:     VecNormBegin(W, NORM_2, &linesearch->xnorm);
     50:     if (!linesearch->ops->vinorm) {VecNormEnd(F, NORM_2, &linesearch->fnorm);}
     51:     VecNormEnd(Y, NORM_2, &linesearch->ynorm);
     52:     VecNormEnd(W, NORM_2, &linesearch->xnorm);

     54:     if (linesearch->ops->vinorm) {
     55:       linesearch->fnorm = gnorm;

     57:       (*linesearch->ops->vinorm)(snes, F, W, &linesearch->fnorm);
     58:     } else {
     59:       VecNorm(F,NORM_2,&linesearch->fnorm);
     60:     }
     61:   }

     63:   /* copy the solution over */
     64:   VecCopy(W, X);
     65:   return(0);
     66: }

     68: /*MC
     69:    SNESLINESEARCHBASIC - This line search implementation is not a line
     70:    search at all; it simply uses the full step.  Thus, this routine is intended
     71:    for methods with well-scaled updates; i.e. Newton's method (SNESNEWTONLS), on
     72:    well-behaved problems.

     74:    Options Database Keys:
     75: +   -snes_linesearch_damping <damping> - search vector is scaled by this amount, default is 1.0
     76: -   -snes_linesearch_norms <flag> - whether to compute norms or not, default is true (SNESLineSearchSetComputeNorms())

     78:    Notes:
     79:    For methods with ill-scaled updates (SNESNRICHARDSON, SNESNCG), a small
     80:    damping parameter may yield satisfactory but slow convergence despite
     81:    the simplicity of the line search.

     83:    Level: advanced

     85: .keywords: SNES, SNESLineSearch, damping

     87: .seealso: SNESLineSearchCreate(), SNESLineSearchSetType(), SNESLineSearchSetDamping(), SNESLineSearchSetComputeNorms()
     88: M*/
     89: PETSC_EXTERN PetscErrorCode SNESLineSearchCreate_Basic(SNESLineSearch linesearch)
     90: {
     92:   linesearch->ops->apply          = SNESLineSearchApply_Basic;
     93:   linesearch->ops->destroy        = NULL;
     94:   linesearch->ops->setfromoptions = NULL;
     95:   linesearch->ops->reset          = NULL;
     96:   linesearch->ops->view           = NULL;
     97:   linesearch->ops->setup          = NULL;
     98:   return(0);
     99: }