Actual source code: bcgs.c


  2: #include <../src/ksp/ksp/impls/bcgs/bcgsimpl.h>

  4: PetscErrorCode KSPSetFromOptions_BCGS(KSP ksp, PetscOptionItems *PetscOptionsObject)
  5: {
  6:   PetscOptionsHeadBegin(PetscOptionsObject, "KSP BCGS Options");
  7:   PetscOptionsHeadEnd();
  8:   return 0;
  9: }

 11: PetscErrorCode KSPSetUp_BCGS(KSP ksp)
 12: {
 13:   KSPSetWorkVecs(ksp, 6);
 14:   return 0;
 15: }

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

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

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

 37:   /* with right preconditioning need to save initial guess to add to final solution */
 38:   if (ksp->pc_side == PC_RIGHT && !ksp->guess_zero) {
 39:     if (!bcgs->guess) VecDuplicate(X, &bcgs->guess);
 40:     VecCopy(X, bcgs->guess);
 41:     VecSet(X, 0.0);
 42:   }

 44:   /* Test for nothing to do */
 45:   if (ksp->normtype != KSP_NORM_NONE) {
 46:     VecNorm(R, NORM_2, &dp);
 47:     KSPCheckNorm(ksp, dp);
 48:   }
 49:   PetscObjectSAWsTakeAccess((PetscObject)ksp);
 50:   ksp->its   = 0;
 51:   ksp->rnorm = dp;
 52:   PetscObjectSAWsGrantAccess((PetscObject)ksp);
 53:   KSPLogResidualHistory(ksp, dp);
 54:   KSPMonitor(ksp, 0, dp);
 55:   (*ksp->converged)(ksp, 0, dp, &ksp->reason, ksp->cnvP);
 56:   if (ksp->reason) {
 57:     if (bcgs->guess) VecAXPY(X, 1.0, bcgs->guess);
 58:     return 0;
 59:   }

 61:   /* Make the initial Rp == R */
 62:   VecCopy(R, RP);

 64:   rhoold   = 1.0;
 65:   alpha    = 1.0;
 66:   omegaold = 1.0;
 67:   VecSet(P, 0.0);
 68:   VecSet(V, 0.0);

 70:   i = 0;
 71:   do {
 72:     VecDot(R, RP, &rho); /*   rho <- (r,rp)      */
 73:     beta = (rho / rhoold) * (alpha / omegaold);
 74:     VecAXPBYPCZ(P, 1.0, -omegaold * beta, beta, R, V); /* p <- r - omega * beta* v + beta * p */
 75:     KSP_PCApplyBAorAB(ksp, P, V, T);                   /*   v <- K p           */
 76:     VecDot(V, RP, &d1);
 77:     KSPCheckDot(ksp, d1);
 78:     if (d1 == 0.0) {
 80:       ksp->reason = KSP_DIVERGED_BREAKDOWN;
 81:       PetscInfo(ksp, "Breakdown due to zero inner product\n");
 82:       break;
 83:     }
 84:     alpha = rho / d1;                           /*   a <- rho / (v,rp)  */
 85:     VecWAXPY(S, -alpha, V, R);       /*   s <- r - a v       */
 86:     KSP_PCApplyBAorAB(ksp, S, T, R); /*   t <- K s    */
 87:     VecDotNorm2(S, T, &d1, &d2);
 88:     if (d2 == 0.0) {
 89:       /* t is 0.  if s is 0, then alpha v == r, and hence alpha p
 90:          may be our solution.  Give it a try? */
 91:       VecDot(S, S, &d1);
 92:       if (d1 != 0.0) {
 94:         ksp->reason = KSP_DIVERGED_BREAKDOWN;
 95:         PetscInfo(ksp, "Failed due to singular preconditioned operator\n");
 96:         break;
 97:       }
 98:       VecAXPY(X, alpha, P); /*   x <- x + a p       */
 99:       PetscObjectSAWsTakeAccess((PetscObject)ksp);
100:       ksp->its++;
101:       ksp->rnorm  = 0.0;
102:       ksp->reason = KSP_CONVERGED_RTOL;
103:       PetscObjectSAWsGrantAccess((PetscObject)ksp);
104:       KSPLogResidualHistory(ksp, dp);
105:       KSPMonitor(ksp, i + 1, 0.0);
106:       break;
107:     }
108:     omega = d1 / d2;                                    /*   w <- (t's) / (t't) */
109:     VecAXPBYPCZ(X, alpha, omega, 1.0, P, S); /* x <- alpha * p + omega * s + x */
110:     VecWAXPY(R, -omega, T, S);               /*   r <- s - w t       */
111:     if (ksp->normtype != KSP_NORM_NONE && ksp->chknorm < i + 2) {
112:       VecNorm(R, NORM_2, &dp);
113:       KSPCheckNorm(ksp, dp);
114:     }

116:     rhoold   = rho;
117:     omegaold = omega;

119:     PetscObjectSAWsTakeAccess((PetscObject)ksp);
120:     ksp->its++;
121:     ksp->rnorm = dp;
122:     PetscObjectSAWsGrantAccess((PetscObject)ksp);
123:     KSPLogResidualHistory(ksp, dp);
124:     KSPMonitor(ksp, i + 1, dp);
125:     (*ksp->converged)(ksp, i + 1, dp, &ksp->reason, ksp->cnvP);
126:     if (ksp->reason) break;
127:     if (rho == 0.0) {
129:       ksp->reason = KSP_DIVERGED_BREAKDOWN;
130:       PetscInfo(ksp, "Breakdown due to zero rho inner product\n");
131:       break;
132:     }
133:     i++;
134:   } while (i < ksp->max_it);

136:   if (i >= ksp->max_it) ksp->reason = KSP_DIVERGED_ITS;

138:   KSPUnwindPreconditioner(ksp, X, T);
139:   if (bcgs->guess) VecAXPY(X, 1.0, bcgs->guess);
140:   return 0;
141: }

143: PetscErrorCode KSPBuildSolution_BCGS(KSP ksp, Vec v, Vec *V)
144: {
145:   KSP_BCGS *bcgs = (KSP_BCGS *)ksp->data;

147:   if (ksp->pc_side == PC_RIGHT) {
148:     if (v) {
149:       KSP_PCApply(ksp, ksp->vec_sol, v);
150:       if (bcgs->guess) VecAXPY(v, 1.0, bcgs->guess);
151:       *V = v;
152:     } else SETERRQ(PetscObjectComm((PetscObject)ksp), PETSC_ERR_SUP, "Not working with right preconditioner");
153:   } else {
154:     if (v) {
155:       VecCopy(ksp->vec_sol, v);
156:       *V = v;
157:     } else *V = ksp->vec_sol;
158:   }
159:   return 0;
160: }

162: PetscErrorCode KSPReset_BCGS(KSP ksp)
163: {
164:   KSP_BCGS *cg = (KSP_BCGS *)ksp->data;

166:   VecDestroy(&cg->guess);
167:   return 0;
168: }

170: PetscErrorCode KSPDestroy_BCGS(KSP ksp)
171: {
172:   KSPReset_BCGS(ksp);
173:   KSPDestroyDefault(ksp);
174:   return 0;
175: }

177: /*MC
178:      KSPBCGS - Implements the BiCGStab (Stabilized version of Biconjugate Gradient) method.

180:    Level: beginner

182:    Notes:
183:    Supports left and right preconditioning but not symmetric

185:    See `KSPBCGSL` for additional stabilization

187:    See `KSPFBCGS`, `KSPFBCGSR`, and `KSPPIPEBCGS` for flexible and pipelined versions of the algorithm

189:    Reference:
190: .  * - van der Vorst, SIAM J. Sci. Stat. Comput., 1992.

192: .seealso: [](chapter_ksp), `KSPFBCGS`, `KSPFBCGSR`, `KSPPIPEBCGS`, `KSPBCGSL`, `KSPCreate()`, `KSPSetType()`, `KSPType`, `KSP`, `KSPBICG`, `KSPBCGSL`, `KSPFBICG`, `KSPQMRCGS`, `KSPSetPCSide()`
193: M*/
194: PETSC_EXTERN PetscErrorCode KSPCreate_BCGS(KSP ksp)
195: {
196:   KSP_BCGS *bcgs;

198:   PetscNew(&bcgs);

200:   ksp->data                = bcgs;
201:   ksp->ops->setup          = KSPSetUp_BCGS;
202:   ksp->ops->solve          = KSPSolve_BCGS;
203:   ksp->ops->destroy        = KSPDestroy_BCGS;
204:   ksp->ops->reset          = KSPReset_BCGS;
205:   ksp->ops->buildsolution  = KSPBuildSolution_BCGS;
206:   ksp->ops->buildresidual  = KSPBuildResidualDefault;
207:   ksp->ops->setfromoptions = KSPSetFromOptions_BCGS;

209:   KSPSetSupportedNorm(ksp, KSP_NORM_PRECONDITIONED, PC_LEFT, 3);
210:   KSPSetSupportedNorm(ksp, KSP_NORM_UNPRECONDITIONED, PC_RIGHT, 2);
211:   KSPSetSupportedNorm(ksp, KSP_NORM_NONE, PC_LEFT, 1);
212:   KSPSetSupportedNorm(ksp, KSP_NORM_NONE, PC_RIGHT, 1);
213:   return 0;
214: }