Actual source code: fbcgs.c


  2: /*
  3:     This file implements flexible BiCGStab (FBiCGStab).
  4:     Only allow right preconditioning.
  5: */
  6: #include <../src/ksp/ksp/impls/bcgs/bcgsimpl.h>

  8: static PetscErrorCode KSPSetUp_FBCGS(KSP ksp)
  9: {
 10:   KSPSetWorkVecs(ksp, 8);
 11:   return 0;
 12: }

 14: /* Only need a few hacks from KSPSolve_BCGS */

 16: static PetscErrorCode KSPSolve_FBCGS(KSP ksp)
 17: {
 18:   PetscInt    i;
 19:   PetscScalar rho, rhoold, alpha, beta, omega, omegaold, d1;
 20:   Vec         X, B, V, P, R, RP, T, S, P2, S2;
 21:   PetscReal   dp   = 0.0, d2;
 22:   KSP_BCGS   *bcgs = (KSP_BCGS *)ksp->data;
 23:   PC          pc;
 24:   Mat         mat;

 26:   X  = ksp->vec_sol;
 27:   B  = ksp->vec_rhs;
 28:   R  = ksp->work[0];
 29:   RP = ksp->work[1];
 30:   V  = ksp->work[2];
 31:   T  = ksp->work[3];
 32:   S  = ksp->work[4];
 33:   P  = ksp->work[5];
 34:   S2 = ksp->work[6];
 35:   P2 = ksp->work[7];

 37:   /* Only supports right preconditioning */
 39:   if (!ksp->guess_zero) {
 40:     if (!bcgs->guess) VecDuplicate(X, &bcgs->guess);
 41:     VecCopy(X, bcgs->guess);
 42:   } else {
 43:     VecSet(X, 0.0);
 44:   }

 46:   /* Compute initial residual */
 47:   KSPGetPC(ksp, &pc);
 48:   PCSetUp(pc);
 49:   PCGetOperators(pc, &mat, NULL);
 50:   if (!ksp->guess_zero) {
 51:     KSP_MatMult(ksp, mat, X, S2);
 52:     VecCopy(B, R);
 53:     VecAXPY(R, -1.0, S2);
 54:   } else {
 55:     VecCopy(B, R);
 56:   }

 58:   /* Test for nothing to do */
 59:   if (ksp->normtype != KSP_NORM_NONE) VecNorm(R, NORM_2, &dp);
 60:   PetscObjectSAWsTakeAccess((PetscObject)ksp);
 61:   ksp->its   = 0;
 62:   ksp->rnorm = dp;
 63:   PetscObjectSAWsGrantAccess((PetscObject)ksp);
 64:   KSPLogResidualHistory(ksp, dp);
 65:   KSPMonitor(ksp, 0, dp);
 66:   (*ksp->converged)(ksp, 0, dp, &ksp->reason, ksp->cnvP);
 67:   if (ksp->reason) return 0;

 69:   /* Make the initial Rp == R */
 70:   VecCopy(R, RP);

 72:   rhoold   = 1.0;
 73:   alpha    = 1.0;
 74:   omegaold = 1.0;
 75:   VecSet(P, 0.0);
 76:   VecSet(V, 0.0);

 78:   i = 0;
 79:   do {
 80:     VecDot(R, RP, &rho); /* rho <- (r,rp) */
 81:     beta = (rho / rhoold) * (alpha / omegaold);
 82:     VecAXPBYPCZ(P, 1.0, -omegaold * beta, beta, R, V); /* p <- r - omega * beta* v + beta * p */

 84:     KSP_PCApply(ksp, P, P2);      /* p2 <- K p */
 85:     KSP_MatMult(ksp, mat, P2, V); /* v <- A p2 */

 87:     VecDot(V, RP, &d1);
 88:     if (d1 == 0.0) {
 90:       ksp->reason = KSP_DIVERGED_BREAKDOWN;
 91:       PetscInfo(ksp, "Breakdown due to zero inner product\n");
 92:       break;
 93:     }
 94:     alpha = rho / d1;                     /* alpha <- rho / (v,rp) */
 95:     VecWAXPY(S, -alpha, V, R); /* s <- r - alpha v */

 97:     KSP_PCApply(ksp, S, S2);      /* s2 <- K s */
 98:     KSP_MatMult(ksp, mat, S2, T); /* t <- A s2 */

100:     VecDotNorm2(S, T, &d1, &d2);
101:     if (d2 == 0.0) {
102:       /* t is 0. if s is 0, then alpha v == r, and hence alpha p may be our solution. Give it a try? */
103:       VecDot(S, S, &d1);
104:       if (d1 != 0.0) {
106:         ksp->reason = KSP_DIVERGED_BREAKDOWN;
107:         PetscInfo(ksp, "Failed due to singular preconditioned operator\n");
108:         break;
109:       }
110:       VecAXPY(X, alpha, P2); /* x <- x + alpha p2 */
111:       PetscObjectSAWsTakeAccess((PetscObject)ksp);
112:       ksp->its++;
113:       ksp->rnorm  = 0.0;
114:       ksp->reason = KSP_CONVERGED_RTOL;
115:       PetscObjectSAWsGrantAccess((PetscObject)ksp);
116:       KSPLogResidualHistory(ksp, dp);
117:       KSPMonitor(ksp, i + 1, 0.0);
118:       break;
119:     }
120:     omega = d1 / d2;                                      /* omega <- (t's) / (t't) */
121:     VecAXPBYPCZ(X, alpha, omega, 1.0, P2, S2); /* x <- alpha * p2 + omega * s2 + x */

123:     VecWAXPY(R, -omega, T, S); /* r <- s - omega t */
124:     if (ksp->normtype != KSP_NORM_NONE && ksp->chknorm < i + 2) VecNorm(R, NORM_2, &dp);

126:     rhoold   = rho;
127:     omegaold = omega;

129:     PetscObjectSAWsTakeAccess((PetscObject)ksp);
130:     ksp->its++;
131:     ksp->rnorm = dp;
132:     PetscObjectSAWsGrantAccess((PetscObject)ksp);
133:     KSPLogResidualHistory(ksp, dp);
134:     KSPMonitor(ksp, i + 1, dp);
135:     (*ksp->converged)(ksp, i + 1, dp, &ksp->reason, ksp->cnvP);
136:     if (ksp->reason) break;
137:     if (rho == 0.0) {
139:       ksp->reason = KSP_DIVERGED_BREAKDOWN;
140:       PetscInfo(ksp, "Breakdown due to zero rho inner product\n");
141:       break;
142:     }
143:     i++;
144:   } while (i < ksp->max_it);

146:   if (i >= ksp->max_it) ksp->reason = KSP_DIVERGED_ITS;
147:   return 0;
148: }

150: /*MC
151:      KSPFBCGS - Implements flexible BiCGStab method.

153:    Options Database Keys:
154:     see KSPSolve()

156:    Level: beginner

158:    Notes:
159:     Only allow right preconditioning

161: .seealso: `KSPCreate()`, `KSPSetType()`, `KSPType`, `KSP`, `KSPBICG`, `KSPFBCGSL`, `KSPSetPCSide()`
162: M*/
163: PETSC_EXTERN PetscErrorCode KSPCreate_FBCGS(KSP ksp)
164: {
165:   KSP_BCGS *bcgs;

167:   PetscNew(&bcgs);

169:   ksp->data                = bcgs;
170:   ksp->ops->setup          = KSPSetUp_FBCGS;
171:   ksp->ops->solve          = KSPSolve_FBCGS;
172:   ksp->ops->destroy        = KSPDestroy_BCGS;
173:   ksp->ops->reset          = KSPReset_BCGS;
174:   ksp->ops->buildresidual  = KSPBuildResidualDefault;
175:   ksp->ops->setfromoptions = KSPSetFromOptions_BCGS;
176:   ksp->pc_side             = PC_RIGHT; /* set default PC side */

178:   KSPSetSupportedNorm(ksp, KSP_NORM_PRECONDITIONED, PC_LEFT, 3);
179:   KSPSetSupportedNorm(ksp, KSP_NORM_UNPRECONDITIONED, PC_RIGHT, 2);
180:   KSPSetSupportedNorm(ksp, KSP_NORM_NONE, PC_LEFT, 1);
181:   KSPSetSupportedNorm(ksp, KSP_NORM_NONE, PC_RIGHT, 1);
182:   return 0;
183: }