Actual source code: bcgs.c
1: /*$Id: bcgs.c,v 1.78 2001/08/07 03:03:49 balay Exp $*/
3: /*
4: This code implements the BiCGStab (Stabilized version of BiConjugate
5: Gradient Squared) method. Reference: van der Vorst, SIAM J. Sci. Stat. Comput., 1992.
7: Note that for the complex numbers version, the VecDot() arguments
8: within the code MUST remain in the order given for correct computation
9: of inner products.
10: */
11: #include src/sles/ksp/kspimpl.h
13: #undef __FUNCT__
15: static int KSPSetUp_BCGS(KSP ksp)
16: {
20: if (ksp->pc_side == PC_SYMMETRIC) {
21: SETERRQ(PETSC_ERR_SUP,"no symmetric preconditioning for KSPBCGS");
22: }
23: KSPDefaultGetWork(ksp,6);
24: return(0);
25: }
27: #undef __FUNCT__
29: static int KSPSolve_BCGS(KSP ksp,int *its)
30: {
31: int i,maxit,ierr;
32: PetscScalar rho,rhoold,alpha,beta,omega,omegaold,d1,d2,zero = 0.0,tmp;
33: Vec X,B,V,P,R,RP,T,S;
34: PetscReal dp = 0.0;
38: maxit = ksp->max_it;
39: X = ksp->vec_sol;
40: B = ksp->vec_rhs;
41: R = ksp->work[0];
42: RP = ksp->work[1];
43: V = ksp->work[2];
44: T = ksp->work[3];
45: S = ksp->work[4];
46: P = ksp->work[5];
48: /* Compute initial preconditioned residual */
49: KSPInitialResidual(ksp,X,V,T,R,B);
51: /* Test for nothing to do */
52: if (ksp->normtype != KSP_NO_NORM) {
53: VecNorm(R,NORM_2,&dp);
54: }
55: PetscObjectTakeAccess(ksp);
56: ksp->its = 0;
57: ksp->rnorm = dp;
58: PetscObjectGrantAccess(ksp);
59: KSPLogResidualHistory(ksp,dp);
60: KSPMonitor(ksp,0,dp);
61: (*ksp->converged)(ksp,0,dp,&ksp->reason,ksp->cnvP);
62: if (ksp->reason) {*its = 0; return(0);}
64: /* Make the initial Rp == R */
65: VecCopy(R,RP);
67: rhoold = 1.0;
68: alpha = 1.0;
69: omegaold = 1.0;
70: VecSet(&zero,P);
71: VecSet(&zero,V);
73: for (i=0; i<maxit; i++) {
75: VecDot(R,RP,&rho); /* rho <- (r,rp) */
76: if (rho == 0.0) SETERRQ(PETSC_ERR_KSP_BRKDWN,"Breakdown, rho = r . rp = 0");
77: beta = (rho/rhoold) * (alpha/omegaold);
78: tmp = -omegaold; VecAXPY(&tmp,V,P); /* p <- p - w v */
79: VecAYPX(&beta,R,P); /* p <- r + p beta */
80: KSP_PCApplyBAorAB(ksp,ksp->B,ksp->pc_side,P,V,T); /* v <- K p */
81: VecDot(V,RP,&d1);
82: alpha = rho / d1; tmp = -alpha; /* a <- rho / (v,rp) */
83: VecWAXPY(&tmp,V,R,S); /* s <- r - a v */
84: KSP_PCApplyBAorAB(ksp,ksp->B,ksp->pc_side,S,T,R);/* t <- K s */
85: VecDot(S,T,&d1);
86: VecDot(T,T,&d2);
87: if (d2 == 0.0) {
88: /* t is 0. if s is 0, then alpha v == r, and hence alpha p
89: may be our solution. Give it a try? */
90: VecDot(S,S,&d1);
91: if (d1 != 0.0) SETERRQ(PETSC_ERR_KSP_BRKDWN,"Breakdown, da = s . s != 0");
92: VecAXPY(&alpha,P,X); /* x <- x + a p */
93: PetscObjectTakeAccess(ksp);
94: ksp->its++;
95: ksp->rnorm = 0.0;
96: ksp->reason = KSP_CONVERGED_RTOL;
97: PetscObjectGrantAccess(ksp);
98: KSPLogResidualHistory(ksp,dp);
99: KSPMonitor(ksp,i+1,0.0);
100: break;
101: }
102: omega = d1 / d2; /* w <- (t's) / (t't) */
103: ierr = VecAXPY(&alpha,P,X); /* x <- x + a p */
104: ierr = VecAXPY(&omega,S,X); /* x <- x + w s */
105: tmp = -omega;
106: ierr = VecWAXPY(&tmp,T,S,R); /* r <- s - w t */
107: if (ksp->normtype != KSP_NO_NORM) {
108: VecNorm(R,NORM_2,&dp);
109: }
111: rhoold = rho;
112: omegaold = omega;
114: PetscObjectTakeAccess(ksp);
115: ksp->its++;
116: ksp->rnorm = dp;
117: PetscObjectGrantAccess(ksp);
118: KSPLogResidualHistory(ksp,dp);
119: KSPMonitor(ksp,i+1,dp);
120: (*ksp->converged)(ksp,i+1,dp,&ksp->reason,ksp->cnvP);
121: if (ksp->reason) break;
122: }
123: if (i == maxit) {
124: ksp->reason = KSP_DIVERGED_ITS;
125: }
126: *its = ksp->its;
128: KSPUnwindPreconditioner(ksp,X,T);
129: return(0);
130: }
132: EXTERN_C_BEGIN
133: #undef __FUNCT__
135: int KSPCreate_BCGS(KSP ksp)
136: {
138: ksp->data = (void*)0;
139: ksp->pc_side = PC_LEFT;
140: ksp->ops->setup = KSPSetUp_BCGS;
141: ksp->ops->solve = KSPSolve_BCGS;
142: ksp->ops->destroy = KSPDefaultDestroy;
143: ksp->ops->buildsolution = KSPDefaultBuildSolution;
144: ksp->ops->buildresidual = KSPDefaultBuildResidual;
145: ksp->ops->setfromoptions = 0;
146: ksp->ops->view = 0;
147: return(0);
148: }
149: EXTERN_C_END