Actual source code: rich.c

  1: #define PETSCKSP_DLL

  3: /*          
  4:             This implements Richardson Iteration.       
  5: */
 6:  #include src/ksp/ksp/kspimpl.h
 7:  #include src/ksp/ksp/impls/rich/richctx.h

 11: PetscErrorCode KSPSetUp_Richardson(KSP ksp)
 12: {

 16:   if (ksp->pc_side == PC_RIGHT) {SETERRQ(PETSC_ERR_SUP,"no right preconditioning for KSPRICHARDSON");}
 17:   else if (ksp->pc_side == PC_SYMMETRIC) {SETERRQ(PETSC_ERR_SUP,"no symmetric preconditioning for KSPRICHARDSON");}
 18:   KSPDefaultGetWork(ksp,2);
 19:   return(0);
 20: }

 24: PetscErrorCode  KSPSolve_Richardson(KSP ksp)
 25: {
 27:   PetscInt       i,maxit;
 28:   MatStructure   pflag;
 29:   PetscReal      rnorm = 0.0;
 30:   PetscScalar    scale,dt;
 31:   Vec            x,b,r,z;
 32:   Mat            Amat,Pmat;
 33:   KSP_Richardson *richardsonP = (KSP_Richardson*)ksp->data;
 34:   PetscTruth     exists,diagonalscale;

 37:   PCDiagonalScale(ksp->pc,&diagonalscale);
 38:   if (diagonalscale) SETERRQ1(PETSC_ERR_SUP,"Krylov method %s does not support diagonal scaling",ksp->type_name);

 40:   ksp->its = 0;

 42:   PCGetOperators(ksp->pc,&Amat,&Pmat,&pflag);
 43:   x       = ksp->vec_sol;
 44:   b       = ksp->vec_rhs;
 45:   r       = ksp->work[0];
 46:   z       = ksp->work[1];
 47:   maxit   = ksp->max_it;

 49:   /* if user has provided fast Richardson code use that */
 50:   PCApplyRichardsonExists(ksp->pc,&exists);
 51:   if (exists && !ksp->numbermonitors && !ksp->transpose_solve) {
 52:     ksp->normtype = KSP_NO_NORM;
 53:     PCApplyRichardson(ksp->pc,b,x,r,ksp->rtol,ksp->abstol,ksp->divtol,maxit);
 54:     if (ksp->normtype != KSP_NO_NORM) {
 55:       KSP_MatMult(ksp,Amat,x,r);
 56:       VecAYPX(r,-1.0,b);
 57:       if (ksp->normtype == KSP_UNPRECONDITIONED_NORM || ksp->pc_side == PC_RIGHT) {
 58:         VecNorm(r,NORM_2,&rnorm); /*   rnorm <- r'*r     */
 59:       } else {
 60:         PetscExceptionTry1((KSP_PCApply(ksp,r,z)),PETSC_ERR_SUP);
 61:         if (PetscExceptionCaught(ierr,PETSC_ERR_SUP)) {
 62:           ksp->reason = KSP_CONVERGED_ITS;
 63:           return(0);
 64:         }
 65:         if (ksp->normtype == KSP_PRECONDITIONED_NORM) {
 66:           VecNorm(z,NORM_2,&rnorm); /*   rnorm <- r'B'*Br     */
 67:         } else {
 68:           VecDot(r,z,&dt);
 69:           rnorm = PetscAbsScalar(dt);                    /*   rnorm <- z'*r  = r'Br = e'*A'*B*A*e  */
 70:         }
 71:       }
 72:       (*ksp->converged)(ksp,0,rnorm,&ksp->reason,ksp->cnvP);
 73:     }
 74:     if (!ksp->reason) ksp->reason = KSP_CONVERGED_ITS;
 75:     return(0);
 76:   }

 78:   scale   = richardsonP->scale;

 80:   if (!ksp->guess_zero) {                          /*   r <- b - A x     */
 81:     KSP_MatMult(ksp,Amat,x,r);
 82:     VecAYPX(r,-1.0,b);
 83:   } else {
 84:     VecCopy(b,r);
 85:   }

 87:   for (i=0; i<maxit; i++) {
 88:     PetscObjectTakeAccess(ksp);
 89:     ksp->its++;
 90:     PetscObjectGrantAccess(ksp);

 92:     if (ksp->normtype == KSP_UNPRECONDITIONED_NORM) {
 93:       VecNorm(r,NORM_2,&rnorm); /*   rnorm <- r'*r     */
 94:       KSPMonitor(ksp,i,rnorm);
 95:     }

 97:     KSP_PCApply(ksp,r,z);    /*   z <- B r          */

 99:     if (ksp->normtype == KSP_PRECONDITIONED_NORM) {
100:       VecNorm(z,NORM_2,&rnorm); /*   rnorm <- z'*z     */
101:       KSPMonitor(ksp,i,rnorm);
102:     }

104:     VecAXPY(x,scale,z);    /*   x  <- x + scale z */
105:     if (ksp->normtype != KSP_NO_NORM) {
106:       PetscObjectTakeAccess(ksp);
107:       ksp->rnorm = rnorm;
108:       PetscObjectGrantAccess(ksp);
109:       KSPLogResidualHistory(ksp,rnorm);

111:       (*ksp->converged)(ksp,i,rnorm,&ksp->reason,ksp->cnvP);
112:       if (ksp->reason) break;
113:     }
114: 
115:     KSP_MatMult(ksp,Amat,x,r);      /*   r  <- b - Ax      */
116:     VecAYPX(r,-1.0,b);
117:   }
118:   if (!ksp->reason) {
119:     ksp->reason = KSP_DIVERGED_ITS;
120:     if (ksp->normtype != KSP_NO_NORM) {
121:       if (ksp->normtype == KSP_UNPRECONDITIONED_NORM){
122:         VecNorm(r,NORM_2,&rnorm);     /*   rnorm <- r'*r     */
123:       } else {
124:         KSP_PCApply(ksp,r,z);   /*   z <- B r          */
125:         VecNorm(z,NORM_2,&rnorm);     /*   rnorm <- z'*z     */
126:       }
127:     }
128:     PetscObjectTakeAccess(ksp);
129:     ksp->rnorm = rnorm;
130:     PetscObjectGrantAccess(ksp);
131:     KSPLogResidualHistory(ksp,rnorm);
132:     KSPMonitor(ksp,i,rnorm);
133:     i--;
134:   } else if (!ksp->reason) {
135:     ksp->reason = KSP_DIVERGED_ITS;
136:   }

138:   return(0);
139: }

143: PetscErrorCode KSPView_Richardson(KSP ksp,PetscViewer viewer)
144: {
145:   KSP_Richardson *richardsonP = (KSP_Richardson*)ksp->data;
147:   PetscTruth     iascii;

150:   PetscTypeCompare((PetscObject)viewer,PETSC_VIEWER_ASCII,&iascii);
151:   if (iascii) {
152:     PetscViewerASCIIPrintf(viewer,"  Richardson: damping factor=%G\n",richardsonP->scale);
153:   } else {
154:     SETERRQ1(PETSC_ERR_SUP,"Viewer type %s not supported for KSP Richardson",((PetscObject)viewer)->type_name);
155:   }
156:   return(0);
157: }

161: PetscErrorCode KSPSetFromOptions_Richardson(KSP ksp)
162: {
163:   KSP_Richardson *rich = (KSP_Richardson*)ksp->data;
165:   PetscReal      tmp;
166:   PetscTruth     flg;

169:   PetscOptionsHead("KSP Richardson Options");
170:     PetscOptionsReal("-ksp_richardson_scale","damping factor","KSPRichardsonSetScale",rich->scale,&tmp,&flg);
171:     if (flg) { KSPRichardsonSetScale(ksp,tmp); }
172:   PetscOptionsTail();
173:   return(0);
174: }

179: PetscErrorCode  KSPRichardsonSetScale_Richardson(KSP ksp,PetscReal scale)
180: {
181:   KSP_Richardson *richardsonP;

184:   richardsonP = (KSP_Richardson*)ksp->data;
185:   richardsonP->scale = scale;
186:   return(0);
187: }

190: /*MC
191:      KSPRICHARDSON - The preconditioned Richardson iterative method

193:    Options Database Keys:
194: .   -ksp_richardson_scale - damping factor on the correction (defaults to 1.0)

196:    Level: beginner

198:    Notes: x^{n+1} = x^{n} + scale*B(b - A x^{n})

200:           This method often (usually) will not converge unless scale is very small

202: .seealso:  KSPCreate(), KSPSetType(), KSPType (for list of available types), KSP,
203:            KSPRichardsonSetScale()

205: M*/

210: PetscErrorCode  KSPCreate_Richardson(KSP ksp)
211: {
213:   KSP_Richardson *richardsonP;

216:   PetscNew(KSP_Richardson,&richardsonP);
217:   PetscLogObjectMemory(ksp,sizeof(KSP_Richardson));
218:   ksp->data                        = (void*)richardsonP;
219:   richardsonP->scale               = 1.0;
220:   ksp->ops->setup                  = KSPSetUp_Richardson;
221:   ksp->ops->solve                  = KSPSolve_Richardson;
222:   ksp->ops->destroy                = KSPDefaultDestroy;
223:   ksp->ops->buildsolution          = KSPDefaultBuildSolution;
224:   ksp->ops->buildresidual          = KSPDefaultBuildResidual;
225:   ksp->ops->view                   = KSPView_Richardson;
226:   ksp->ops->setfromoptions         = KSPSetFromOptions_Richardson;

228:   PetscObjectComposeFunctionDynamic((PetscObject)ksp,"KSPRichardsonSetScale_C",
229:                                     "KSPRichardsonSetScale_Richardson",
230:                                     KSPRichardsonSetScale_Richardson);
231:   return(0);
232: }