Actual source code: bcgs.c

  1: /*$Id: bcgs.c,v 1.78 2001/08/07 03:03:49 balay Exp $*/

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

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


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

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

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

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

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

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

102:     rhoold   = rho;
103:     omegaold = omega;

105:     PetscObjectTakeAccess(ksp);
106:     ksp->its++;
107:     ksp->rnorm = dp;
108:     PetscObjectGrantAccess(ksp);
109:     KSPLogResidualHistory(ksp,dp);
110:     KSPMonitor(ksp,i+1,dp);
111:     (*ksp->converged)(ksp,i+1,dp,&ksp->reason,ksp->cnvP);
112:     if (ksp->reason) break;
113:     i++;
114:   } while (i<ksp->max_it);

116:   if (i == ksp->max_it) {
117:     ksp->reason = KSP_DIVERGED_ITS;
118:   }

120:   KSPUnwindPreconditioner(ksp,X,T);
121:   return(0);
122: }

124: /*MC
125:      KSPBCGS -     Implements the BiCGStab (Stabilized version of BiConjugate
126:          Gradient Squared) method.  Reference: van der Vorst, SIAM J. Sci. Stat. Comput., 1992.


129:    Options Database Keys:
130: .   see KSPSolve()

132:    Level: beginner

134: .seealso:  KSPCreate(), KSPSetType(), KSPType (for list of available types), KSP, KSPBICG

136: M*/

138: EXTERN_C_BEGIN
141: int KSPCreate_BCGS(KSP ksp)
142: {
144:   ksp->data                 = (void*)0;
145:   ksp->pc_side              = PC_LEFT;
146:   ksp->ops->setup           = KSPSetUp_BCGS;
147:   ksp->ops->solve           = KSPSolve_BCGS;
148:   ksp->ops->destroy         = KSPDefaultDestroy;
149:   ksp->ops->buildsolution   = KSPDefaultBuildSolution;
150:   ksp->ops->buildresidual   = KSPDefaultBuildResidual;
151:   ksp->ops->setfromoptions  = 0;
152:   ksp->ops->view            = 0;
153:   return(0);
154: }
155: EXTERN_C_END