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: static int KSPSetUp_BCGS(KSP ksp)
14: {
18: if (ksp->pc_side == PC_SYMMETRIC) {
19: SETERRQ(PETSC_ERR_SUP,"no symmetric preconditioning for KSPBCGS");
20: }
21: KSPDefaultGetWork(ksp,6);
22: return(0);
23: }
25: static int KSPSolve_BCGS(KSP ksp,int *its)
26: {
27: int i,maxit,ierr;
28: PetscScalar rho,rhoold,alpha,beta,omega,omegaold,d1,d2,zero = 0.0,tmp;
29: Vec X,B,V,P,R,RP,T,S;
30: PetscReal dp = 0.0;
34: maxit = ksp->max_it;
35: X = ksp->vec_sol;
36: B = ksp->vec_rhs;
37: R = ksp->work[0];
38: RP = ksp->work[1];
39: V = ksp->work[2];
40: T = ksp->work[3];
41: S = ksp->work[4];
42: P = ksp->work[5];
44: /* Compute initial preconditioned residual */
45: KSPInitialResidual(ksp,X,V,T,R,B);
47: /* Test for nothing to do */
48: if (ksp->normtype != KSP_NO_NORM) {
49: VecNorm(R,NORM_2,&dp);
50: }
51: PetscObjectTakeAccess(ksp);
52: ksp->its = 0;
53: ksp->rnorm = dp;
54: PetscObjectGrantAccess(ksp);
55: KSPLogResidualHistory(ksp,dp);
56: KSPMonitor(ksp,0,dp);
57: (*ksp->converged)(ksp,0,dp,&ksp->reason,ksp->cnvP);
58: if (ksp->reason) {*its = 0; return(0);}
60: /* Make the initial Rp == R */
61: VecCopy(R,RP);
63: rhoold = 1.0;
64: alpha = 1.0;
65: omegaold = 1.0;
66: VecSet(&zero,P);
67: VecSet(&zero,V);
69: for (i=0; i<maxit; i++) {
71: VecDot(R,RP,&rho); /* rho <- (r,rp) */
72: if (rho == 0.0) SETERRQ(PETSC_ERR_KSP_BRKDWN,"Breakdown, rho = r . rp = 0");
73: beta = (rho/rhoold) * (alpha/omegaold);
74: tmp = -omegaold; VecAXPY(&tmp,V,P); /* p <- p - w v */
75: VecAYPX(&beta,R,P); /* p <- r + p beta */
76: KSP_PCApplyBAorAB(ksp,ksp->B,ksp->pc_side,P,V,T); /* v <- K p */
77: VecDot(V,RP,&d1);
78: alpha = rho / d1; tmp = -alpha; /* a <- rho / (v,rp) */
79: VecWAXPY(&tmp,V,R,S); /* s <- r - a v */
80: KSP_PCApplyBAorAB(ksp,ksp->B,ksp->pc_side,S,T,R);/* t <- K s */
81: VecDot(S,T,&d1);
82: VecDot(T,T,&d2);
83: if (d2 == 0.0) {
84: /* t is 0. if s is 0, then alpha v == r, and hence alpha p
85: may be our solution. Give it a try? */
86: VecDot(S,S,&d1);
87: if (d1 != 0.0) SETERRQ(PETSC_ERR_KSP_BRKDWN,"Breakdown, da = s . s != 0");
88: VecAXPY(&alpha,P,X); /* x <- x + a p */
89: PetscObjectTakeAccess(ksp);
90: ksp->its++;
91: ksp->rnorm = 0.0;
92: ksp->reason = KSP_CONVERGED_RTOL;
93: PetscObjectGrantAccess(ksp);
94: KSPLogResidualHistory(ksp,dp);
95: KSPMonitor(ksp,i+1,0.0);
96: break;
97: }
98: omega = d1 / d2; /* w <- (t's) / (t't) */
99: ierr = VecAXPY(&alpha,P,X); /* x <- x + a p */
100: ierr = VecAXPY(&omega,S,X); /* x <- x + w s */
101: tmp = -omega;
102: ierr = VecWAXPY(&tmp,T,S,R); /* r <- s - w t */
103: if (ksp->normtype != KSP_NO_NORM) {
104: VecNorm(R,NORM_2,&dp);
105: }
107: rhoold = rho;
108: omegaold = omega;
110: PetscObjectTakeAccess(ksp);
111: ksp->its++;
112: ksp->rnorm = dp;
113: PetscObjectGrantAccess(ksp);
114: KSPLogResidualHistory(ksp,dp);
115: KSPMonitor(ksp,i+1,dp);
116: (*ksp->converged)(ksp,i+1,dp,&ksp->reason,ksp->cnvP);
117: if (ksp->reason) break;
118: }
119: if (i == maxit) {
120: ksp->reason = KSP_DIVERGED_ITS;
121: i--;
122: }
123: *its = i+1;
125: KSPUnwindPreconditioner(ksp,X,T);
126: return(0);
127: }
129: EXTERN_C_BEGIN
130: int KSPCreate_BCGS(KSP ksp)
131: {
133: ksp->data = (void*)0;
134: ksp->pc_side = PC_LEFT;
135: ksp->ops->setup = KSPSetUp_BCGS;
136: ksp->ops->solve = KSPSolve_BCGS;
137: ksp->ops->destroy = KSPDefaultDestroy;
138: ksp->ops->buildsolution = KSPDefaultBuildSolution;
139: ksp->ops->buildresidual = KSPDefaultBuildResidual;
140: ksp->ops->setfromoptions = 0;
141: ksp->ops->view = 0;
142: return(0);
143: }
144: EXTERN_C_END