Actual source code: bcgs.c

  1: #define PETSCKSP_DLL

 3:  #include src/ksp/ksp/kspimpl.h

  7: static PetscErrorCode KSPSetUp_BCGS(KSP ksp)
  8: {

 12:   if (ksp->pc_side == PC_SYMMETRIC) {
 13:     SETERRQ(PETSC_ERR_SUP,"no symmetric preconditioning for KSPBCGS");
 14:   }
 15:   KSPDefaultGetWork(ksp,6);
 16:   return(0);
 17: }

 21: static PetscErrorCode  KSPSolve_BCGS(KSP ksp)
 22: {
 24:   PetscInt       i;
 25:   PetscScalar    rho,rhoold,alpha,beta,omega,omegaold,d1,d2,zero = 0.0,tmp;
 26:   Vec            X,B,V,P,R,RP,T,S;
 27:   PetscReal      dp = 0.0;


 31:   X       = ksp->vec_sol;
 32:   B       = ksp->vec_rhs;
 33:   R       = ksp->work[0];
 34:   RP      = ksp->work[1];
 35:   V       = ksp->work[2];
 36:   T       = ksp->work[3];
 37:   S       = ksp->work[4];
 38:   P       = ksp->work[5];

 40:   /* Compute initial preconditioned residual */
 41:   KSPInitialResidual(ksp,X,V,T,R,B);

 43:   /* Test for nothing to do */
 44:   if (ksp->normtype != KSP_NO_NORM) {
 45:     VecNorm(R,NORM_2,&dp);
 46:   }
 47:   PetscObjectTakeAccess(ksp);
 48:   ksp->its   = 0;
 49:   ksp->rnorm = dp;
 50:   PetscObjectGrantAccess(ksp);
 51:   KSPLogResidualHistory(ksp,dp);
 52:   KSPMonitor(ksp,0,dp);
 53:   (*ksp->converged)(ksp,0,dp,&ksp->reason,ksp->cnvP);
 54:   if (ksp->reason) return(0);

 56:   /* Make the initial Rp == R */
 57:   VecCopy(R,RP);

 59:   rhoold   = 1.0;
 60:   alpha    = 1.0;
 61:   omegaold = 1.0;
 62:   VecSet(P,zero);
 63:   VecSet(V,zero);

 65:   i=0;
 66:   do {
 67:     VecDot(R,RP,&rho);       /*   rho <- (r,rp)      */
 68:     if (rho == 0.0) {
 69:       ksp->reason = KSP_DIVERGED_BREAKDOWN;
 70:       break;
 71:     }
 72:     beta = (rho/rhoold) * (alpha/omegaold);
 73:     tmp = -omegaold; VecAXPY(P,tmp,V);            /*   p <- p - w v       */
 74:     VecAYPX(P,beta,R);      /*   p <- r + p beta    */
 75:     KSP_PCApplyBAorAB(ksp,P,V,T);  /*   v <- K p           */
 76:     VecDot(V,RP,&d1);
 77:     alpha = rho / d1; tmp = -alpha;                /*   a <- rho / (v,rp)  */
 78:     VecWAXPY(S,tmp,V,R);      /*   s <- r - a v       */
 79:     KSP_PCApplyBAorAB(ksp,S,T,R);/*   t <- K s    */
 80:     VecDot(S,T,&d1);
 81:     VecDot(T,T,&d2);
 82:     if (d2 == 0.0) {
 83:       /* t is 0.  if s is 0, then alpha v == r, and hence alpha p
 84:          may be our solution.  Give it a try? */
 85:       VecDot(S,S,&d1);
 86:       if (d1 == 0.0) {
 87:         ksp->reason = KSP_DIVERGED_BREAKDOWN;
 88:         break;
 89:       }
 90:       VecAXPY(X,alpha,P);   /*   x <- x + a p       */
 91:       PetscObjectTakeAccess(ksp);
 92:       ksp->its++;
 93:       ksp->rnorm  = 0.0;
 94:       ksp->reason = KSP_CONVERGED_RTOL;
 95:       PetscObjectGrantAccess(ksp);
 96:       KSPLogResidualHistory(ksp,dp);
 97:       KSPMonitor(ksp,i+1,0.0);
 98:       break;
 99:     }
100:     omega = d1 / d2;                               /*   w <- (t's) / (t't) */
101:     VecAXPY(X,alpha,P);     /*   x <- x + a p       */
102:     VecAXPY(X,omega,S);     /*   x <- x + w s       */
103:     tmp   = -omega;
104:     VecWAXPY(R,tmp,T,S);     /*   r <- s - w t       */
105:     if (ksp->normtype != KSP_NO_NORM) {
106:       VecNorm(R,NORM_2,&dp);
107:     }

109:     rhoold   = rho;
110:     omegaold = omega;

112:     PetscObjectTakeAccess(ksp);
113:     ksp->its++;
114:     ksp->rnorm = dp;
115:     PetscObjectGrantAccess(ksp);
116:     KSPLogResidualHistory(ksp,dp);
117:     KSPMonitor(ksp,i+1,dp);
118:     (*ksp->converged)(ksp,i+1,dp,&ksp->reason,ksp->cnvP);
119:     if (ksp->reason) break;
120:     i++;
121:   } while (i<ksp->max_it);

123:   if (i >= ksp->max_it) {
124:     ksp->reason = KSP_DIVERGED_ITS;
125:   }

127:   KSPUnwindPreconditioner(ksp,X,T);
128:   return(0);
129: }

131: /*MC
132:      KSPBCGS - Implements the BiCGStab (Stabilized version of BiConjugate Gradient Squared) method.

134:    Options Database Keys:
135: .   see KSPSolve()

137:    Level: beginner

139:    Notes: Reference: van der Vorst, SIAM J. Sci. Stat. Comput., 1992.
140:           See KSPBCGSL for additional stabilization

142: .seealso:  KSPCreate(), KSPSetType(), KSPType (for list of available types), KSP, KSPBICG, KSPBCGSL
143: M*/
147: PetscErrorCode PETSCKSP_DLLEXPORT KSPCreate_BCGS(KSP ksp)
148: {
150:   ksp->data                 = (void*)0;
151:   ksp->pc_side              = PC_LEFT;
152:   ksp->ops->setup           = KSPSetUp_BCGS;
153:   ksp->ops->solve           = KSPSolve_BCGS;
154:   ksp->ops->destroy         = KSPDefaultDestroy;
155:   ksp->ops->buildsolution   = KSPDefaultBuildSolution;
156:   ksp->ops->buildresidual   = KSPDefaultBuildResidual;
157:   ksp->ops->setfromoptions  = 0;
158:   ksp->ops->view            = 0;
159:   return(0);
160: }