Actual source code: kaczmarz.c
petsc-3.10.5 2019-03-28
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      1:  #include <petsc/private/pcimpl.h>

      3: typedef struct {
      4:   PetscReal  lambda; /* damping parameter */
      5:   PetscBool  symmetric; /* apply the projections symmetrically */
      6: } PC_Kaczmarz;

      8: static PetscErrorCode PCDestroy_Kaczmarz(PC pc)
      9: {

     13:   PetscFree(pc->data);
     14:   return(0);
     15: }

     17: static PetscErrorCode PCApply_Kaczmarz(PC pc,Vec x,Vec y)
     18: {
     19:   PC_Kaczmarz       *jac = (PC_Kaczmarz*)pc->data;
     20:   PetscInt          xs,xe,ys,ye,ncols,i,j;
     21:   const PetscInt    *cols;
     22:   const PetscScalar *vals,*xarray;
     23:   PetscErrorCode    ierr;
     24:   PetscScalar       r;
     25:   PetscReal         anrm;
     26:   PetscScalar       *yarray;
     27:   PetscReal         lambda=jac->lambda;

     30:   MatGetOwnershipRange(pc->pmat,&xs,&xe);
     31:   MatGetOwnershipRangeColumn(pc->pmat,&ys,&ye);
     32:   VecSet(y,0.);
     33:   VecGetArrayRead(x,&xarray);
     34:   VecGetArray(y,&yarray);
     35:   for (i=xs;i<xe;i++) {
     36:     /* get the maximum row width and row norms */
     37:     MatGetRow(pc->pmat,i,&ncols,&cols,&vals);
     38:     r = xarray[i-xs];
     39:     anrm = 0.;
     40:     for (j=0;j<ncols;j++) {
     41:       if (cols[j] >= ys && cols[j] < ye) {
     42:         r -= yarray[cols[j]-ys]*vals[j];
     43:       }
     44:       anrm += PetscRealPart(PetscSqr(vals[j]));
     45:     }
     46:     if (anrm > 0.) {
     47:       for (j=0;j<ncols;j++) {
     48:         if (cols[j] >= ys && cols[j] < ye) {
     49:           yarray[cols[j]-ys] += vals[j]*lambda*r/anrm;
     50:         }
     51:       }
     52:     }
     53:     MatRestoreRow(pc->pmat,i,&ncols,&cols,&vals);
     54:   }
     55:   if (jac->symmetric) {
     56:     for (i=xe-1;i>=xs;i--) {
     57:       MatGetRow(pc->pmat,i,&ncols,&cols,&vals);
     58:       r = xarray[i-xs];
     59:       anrm = 0.;
     60:       for (j=0;j<ncols;j++) {
     61:         if (cols[j] >= ys && cols[j] < ye) {
     62:           r -= yarray[cols[j]-ys]*vals[j];
     63:         }
     64:         anrm += PetscRealPart(PetscSqr(vals[j]));
     65:       }
     66:       if (anrm > 0.) {
     67:         for (j=0;j<ncols;j++) {
     68:           if (cols[j] >= ys && cols[j] < ye) {
     69:             yarray[cols[j]-ys] += vals[j]*lambda*r/anrm;
     70:           }
     71:         }
     72:       }
     73:       MatRestoreRow(pc->pmat,i,&ncols,&cols,&vals);
     74:     }
     75:   }
     76:   VecRestoreArray(y,&yarray);
     77:   VecRestoreArrayRead(x,&xarray);
     78:   return(0);
     79: }

     81: PetscErrorCode PCSetFromOptions_Kaczmarz(PetscOptionItems *PetscOptionsObject,PC pc)
     82: {
     83:   PC_Kaczmarz    *jac = (PC_Kaczmarz*)pc->data;

     87:   PetscOptionsHead(PetscOptionsObject,"Kaczmarz options");
     88:   PetscOptionsReal("-pc_kaczmarz_lambda","relaxation factor (0 < lambda)","",jac->lambda,&jac->lambda,NULL);
     89:   PetscOptionsBool("-pc_kaczmarz_symmetric","apply row projections symmetrically","",jac->symmetric,&jac->symmetric,NULL);
     90:   PetscOptionsTail();
     91:   return(0);
     92: }

     94: PetscErrorCode PCView_Kaczmarz(PC pc,PetscViewer viewer)
     95: {
     96:   PC_Kaczmarz    *jac = (PC_Kaczmarz*)pc->data;
     98:   PetscBool      iascii;

    101:   PetscObjectTypeCompare((PetscObject)viewer,PETSCVIEWERASCII,&iascii);
    102:   if (iascii) {
    103:     PetscViewerASCIIPrintf(viewer,"  lambda = %g\n",(double)jac->lambda);
    104:   }
    105:   return(0);
    106: }

    108: /*MC
    109:      PCKaczmarz - Kaczmarz iteration

    111:    Options Database Keys:
    112: .  -pc_sor_lambda <1.0> - Sets damping parameter lambda

    114:    Level: beginner

    116:    Concepts: Kaczmarz, preconditioners, row projection

    118:    Notes:
    119:     In parallel this is block-Jacobi with Kaczmarz inner solve.

    121:    References:
    122: .  1. - S. Kaczmarz, "Angenaherte Auflosing von Systemen Linearer Gleichungen",
    123:    Bull. Internat. Acad. Polon. Sci. C1. A, 1937.

    125: .seealso:  PCCreate(), PCSetType(), PCType (for list of available types), PC

    127: M*/

    129: PETSC_EXTERN PetscErrorCode PCCreate_Kaczmarz(PC pc)
    130: {
    132:   PC_Kaczmarz    *jac;

    135:   PetscNewLog(pc,&jac);

    137:   pc->ops->apply           = PCApply_Kaczmarz;
    138:   pc->ops->setfromoptions  = PCSetFromOptions_Kaczmarz;
    139:   pc->ops->setup           = 0;
    140:   pc->ops->view            = PCView_Kaczmarz;
    141:   pc->ops->destroy         = PCDestroy_Kaczmarz;
    142:   pc->data                 = (void*)jac;
    143:   jac->lambda              = 1.0;
    144:   jac->symmetric           = PETSC_FALSE;
    145:   return(0);
    146: }