Actual source code: cr.c

petsc-master 2020-09-26
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  2: #include <petsc/private/kspimpl.h>

  4: static PetscErrorCode KSPSetUp_CR(KSP ksp)
  5: {

  9:   if (ksp->pc_side == PC_RIGHT) SETERRQ(PetscObjectComm((PetscObject)ksp),PETSC_ERR_SUP,"no right preconditioning for KSPCR");
 10:   else if (ksp->pc_side == PC_SYMMETRIC) SETERRQ(PETSC_COMM_SELF,PETSC_ERR_SUP,"no symmetric preconditioning for KSPCR");
 11:   KSPSetWorkVecs(ksp,6);
 12:   return(0);
 13: }

 15: static PetscErrorCode  KSPSolve_CR(KSP ksp)
 16: {
 18:   PetscInt       i = 0;
 19:   PetscReal      dp;
 20:   PetscScalar    ai, bi;
 21:   PetscScalar    apq,btop, bbot;
 22:   Vec            X,B,R,RT,P,AP,ART,Q;
 23:   Mat            Amat, Pmat;

 26:   X   = ksp->vec_sol;
 27:   B   = ksp->vec_rhs;
 28:   R   = ksp->work[0];
 29:   RT  = ksp->work[1];
 30:   P   = ksp->work[2];
 31:   AP  = ksp->work[3];
 32:   ART = ksp->work[4];
 33:   Q   = ksp->work[5];

 35:   /* R is the true residual norm, RT is the preconditioned residual norm */
 36:   PCGetOperators(ksp->pc,&Amat,&Pmat);
 37:   if (!ksp->guess_zero) {
 38:     KSP_MatMult(ksp,Amat,X,R);     /*   R <- A*X           */
 39:     VecAYPX(R,-1.0,B);            /*   R <- B-R == B-A*X  */
 40:   } else {
 41:     VecCopy(B,R);                  /*   R <- B (X is 0)    */
 42:   }
 43:   KSP_PCApply(ksp,R,P);     /*   P   <- B*R         */
 44:   KSP_MatMult(ksp,Amat,P,AP);      /*   AP  <- A*P         */
 45:   VecCopy(P,RT);                   /*   RT  <- P           */
 46:   VecCopy(AP,ART);                 /*   ART <- AP          */
 47:   VecDotBegin(RT,ART,&btop);          /*   (RT,ART)           */

 49:   if (ksp->normtype == KSP_NORM_PRECONDITIONED) {
 50:     VecNormBegin(RT,NORM_2,&dp);        /*   dp <- RT'*RT       */
 51:     VecDotEnd   (RT,ART,&btop);           /*   (RT,ART)           */
 52:     VecNormEnd  (RT,NORM_2,&dp);        /*   dp <- RT'*RT       */
 53:     KSPCheckNorm(ksp,dp);
 54:   } else if (ksp->normtype == KSP_NORM_NONE) {
 55:     dp   = 0.0; /* meaningless value that is passed to monitor and convergence test */
 56:     VecDotEnd   (RT,ART,&btop);           /*   (RT,ART)           */
 57:   } else if (ksp->normtype == KSP_NORM_UNPRECONDITIONED) {
 58:     VecNormBegin(R,NORM_2,&dp);         /*   dp <- R'*R         */
 59:     VecDotEnd   (RT,ART,&btop);          /*   (RT,ART)           */
 60:     VecNormEnd  (R,NORM_2,&dp);        /*   dp <- RT'*RT       */
 61:     KSPCheckNorm(ksp,dp);
 62:   } else if (ksp->normtype == KSP_NORM_NATURAL) {
 63:     VecDotEnd   (RT,ART,&btop);           /*   (RT,ART)           */
 64:     dp   = PetscSqrtReal(PetscAbsScalar(btop));                  /* dp = sqrt(R,AR)      */
 65:   } else SETERRQ1(PetscObjectComm((PetscObject)ksp),PETSC_ERR_SUP,"KSPNormType of %d not supported",(int)ksp->normtype);
 66:   if (PetscAbsScalar(btop) < 0.0) {
 67:     ksp->reason = KSP_DIVERGED_INDEFINITE_MAT;
 68:     PetscInfo(ksp,"diverging due to indefinite or negative definite matrix\n");
 69:     return(0);
 70:   }

 72:   ksp->its   = 0;
 73:   KSPMonitor(ksp,0,dp);
 74:   PetscObjectSAWsTakeAccess((PetscObject)ksp);
 75:   ksp->rnorm = dp;
 76:   PetscObjectSAWsGrantAccess((PetscObject)ksp);
 77:   KSPLogResidualHistory(ksp,dp);
 78:   (*ksp->converged)(ksp,0,dp,&ksp->reason,ksp->cnvP);
 79:   if (ksp->reason) return(0);

 81:   i = 0;
 82:   do {
 83:     KSP_PCApply(ksp,AP,Q);  /*   Q <- B* AP          */

 85:     VecDot(AP,Q,&apq);
 86:     KSPCheckDot(ksp,apq);
 87:     if (PetscRealPart(apq) <= 0.0) {
 88:       ksp->reason = KSP_DIVERGED_INDEFINITE_PC;
 89:       PetscInfo(ksp,"KSPSolve_CR:diverging due to indefinite or negative definite PC\n");
 90:       break;
 91:     }
 92:     ai = btop/apq;                                      /* ai = (RT,ART)/(AP,Q)  */

 94:     VecAXPY(X,ai,P);              /*   X   <- X + ai*P     */
 95:     VecAXPY(RT,-ai,Q);             /*   RT  <- RT - ai*Q    */
 96:     KSP_MatMult(ksp,Amat,RT,ART);  /*   ART <-   A*RT       */
 97:     bbot = btop;
 98:     VecDotBegin(RT,ART,&btop);

100:     if (ksp->normtype == KSP_NORM_PRECONDITIONED) {
101:       VecNormBegin(RT,NORM_2,&dp);      /*   dp <- || RT ||      */
102:       VecDotEnd   (RT,ART,&btop);
103:       VecNormEnd  (RT,NORM_2,&dp);      /*   dp <- || RT ||      */
104:       KSPCheckNorm(ksp,dp);
105:     } else if (ksp->normtype == KSP_NORM_NATURAL) {
106:       VecDotEnd(RT,ART,&btop);
107:       dp   = PetscSqrtReal(PetscAbsScalar(btop));                /* dp = sqrt(R,AR)       */
108:     } else if (ksp->normtype == KSP_NORM_NONE) {
109:       VecDotEnd(RT,ART,&btop);
110:       dp   = 0.0; /* meaningless value that is passed to monitor and convergence test */
111:     } else if (ksp->normtype == KSP_NORM_UNPRECONDITIONED) {
112:       VecAXPY(R,ai,AP);           /*   R   <- R - ai*AP    */
113:       VecNormBegin(R,NORM_2,&dp);       /*   dp <- R'*R          */
114:       VecDotEnd   (RT,ART,&btop);
115:       VecNormEnd  (R,NORM_2,&dp);       /*   dp <- R'*R          */
116:       KSPCheckNorm(ksp,dp);
117:     } else SETERRQ1(PetscObjectComm((PetscObject)ksp),PETSC_ERR_SUP,"KSPNormType of %d not supported",(int)ksp->normtype);
118:     if (PetscAbsScalar(btop) < 0.0) {
119:       ksp->reason = KSP_DIVERGED_INDEFINITE_MAT;
120:       PetscInfo(ksp,"diverging due to indefinite or negative definite PC\n");
121:       break;
122:     }

124:     PetscObjectSAWsTakeAccess((PetscObject)ksp);
125:     ksp->its++;
126:     ksp->rnorm = dp;
127:     PetscObjectSAWsGrantAccess((PetscObject)ksp);

129:     KSPLogResidualHistory(ksp,dp);
130:     KSPMonitor(ksp,i+1,dp);
131:     (*ksp->converged)(ksp,i+1,dp,&ksp->reason,ksp->cnvP);
132:     if (ksp->reason) break;

134:     bi   = btop/bbot;
135:     VecAYPX(P,bi,RT);              /*   P <- RT + Bi P     */
136:     VecAYPX(AP,bi,ART);            /*   AP <- ART + Bi AP  */
137:     i++;
138:   } while (i<ksp->max_it);
139:   if (i >= ksp->max_it) ksp->reason =  KSP_DIVERGED_ITS;
140:   return(0);
141: }


144: /*MC
145:      KSPCR - This code implements the (preconditioned) conjugate residuals method

147:    Options Database Keys:
148: .   see KSPSolve()

150:    Level: beginner

152:    Notes:
153:     The operator and the preconditioner must be symmetric for this method. The
154:           preconditioner must be POSITIVE-DEFINITE and the operator POSITIVE-SEMIDEFINITE.
155:           Support only for left preconditioning.

157:    References:
158: .   1. - Magnus R. Hestenes and Eduard Stiefel, Methods of Conjugate Gradients for Solving Linear Systems,
159:    Journal of Research of the National Bureau of Standards Vol. 49, No. 6, December 1952 Research Paper 2379

161: .seealso: KSPCreate(), KSPSetType(), KSPType (for list of available types), KSP, KSPCG
162: M*/
163: PETSC_EXTERN PetscErrorCode KSPCreate_CR(KSP ksp)
164: {

168:   KSPSetSupportedNorm(ksp,KSP_NORM_PRECONDITIONED,PC_LEFT,3);
169:   KSPSetSupportedNorm(ksp,KSP_NORM_UNPRECONDITIONED,PC_LEFT,2);
170:   KSPSetSupportedNorm(ksp,KSP_NORM_NATURAL,PC_LEFT,2);
171:   KSPSetSupportedNorm(ksp,KSP_NORM_NONE,PC_LEFT,1);

173:   ksp->ops->setup          = KSPSetUp_CR;
174:   ksp->ops->solve          = KSPSolve_CR;
175:   ksp->ops->destroy        = KSPDestroyDefault;
176:   ksp->ops->buildsolution  = KSPBuildSolutionDefault;
177:   ksp->ops->buildresidual  = KSPBuildResidualDefault;
178:   ksp->ops->setfromoptions = NULL;
179:   ksp->ops->view           = NULL;
180:   return(0);
181: }