Actual source code: bcgs.c


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

  4: PetscErrorCode KSPSetFromOptions_BCGS(KSP ksp, PetscOptionItems *PetscOptionsObject)
  5: {
  6:   PetscFunctionBegin;
  7:   PetscOptionsHeadBegin(PetscOptionsObject, "KSP BCGS Options");
  8:   PetscOptionsHeadEnd();
  9:   PetscFunctionReturn(PETSC_SUCCESS);
 10: }

 12: PetscErrorCode KSPSetUp_BCGS(KSP ksp)
 13: {
 14:   PetscFunctionBegin;
 15:   PetscCall(KSPSetWorkVecs(ksp, 6));
 16:   PetscFunctionReturn(PETSC_SUCCESS);
 17: }

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

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

 37:   /* Compute initial preconditioned residual */
 38:   PetscCall(KSPInitialResidual(ksp, X, V, T, R, B));

 40:   /* with right preconditioning need to save initial guess to add to final solution */
 41:   if (ksp->pc_side == PC_RIGHT && !ksp->guess_zero) {
 42:     if (!bcgs->guess) PetscCall(VecDuplicate(X, &bcgs->guess));
 43:     PetscCall(VecCopy(X, bcgs->guess));
 44:     PetscCall(VecSet(X, 0.0));
 45:   }

 47:   /* Test for nothing to do */
 48:   if (ksp->normtype != KSP_NORM_NONE) {
 49:     PetscCall(VecNorm(R, NORM_2, &dp));
 50:     KSPCheckNorm(ksp, dp);
 51:   }
 52:   PetscCall(PetscObjectSAWsTakeAccess((PetscObject)ksp));
 53:   ksp->its   = 0;
 54:   ksp->rnorm = dp;
 55:   PetscCall(PetscObjectSAWsGrantAccess((PetscObject)ksp));
 56:   PetscCall(KSPLogResidualHistory(ksp, dp));
 57:   PetscCall(KSPMonitor(ksp, 0, dp));
 58:   PetscCall((*ksp->converged)(ksp, 0, dp, &ksp->reason, ksp->cnvP));
 59:   if (ksp->reason) {
 60:     if (bcgs->guess) PetscCall(VecAXPY(X, 1.0, bcgs->guess));
 61:     PetscFunctionReturn(PETSC_SUCCESS);
 62:   }

 64:   /* Make the initial Rp == R */
 65:   PetscCall(VecCopy(R, RP));

 67:   rhoold   = 1.0;
 68:   alpha    = 1.0;
 69:   omegaold = 1.0;
 70:   PetscCall(VecSet(P, 0.0));
 71:   PetscCall(VecSet(V, 0.0));

 73:   i = 0;
 74:   do {
 75:     PetscCall(VecDot(R, RP, &rho)); /*   rho <- (r,rp)      */
 76:     beta = (rho / rhoold) * (alpha / omegaold);
 77:     PetscCall(VecAXPBYPCZ(P, 1.0, -omegaold * beta, beta, R, V)); /* p <- r - omega * beta* v + beta * p */
 78:     PetscCall(KSP_PCApplyBAorAB(ksp, P, V, T));                   /*   v <- K p           */
 79:     PetscCall(VecDot(V, RP, &d1));
 80:     KSPCheckDot(ksp, d1);
 81:     if (d1 == 0.0) {
 82:       PetscCheck(!ksp->errorifnotconverged, PetscObjectComm((PetscObject)ksp), PETSC_ERR_NOT_CONVERGED, "KSPSolve breakdown due to zero inner product");
 83:       ksp->reason = KSP_DIVERGED_BREAKDOWN;
 84:       PetscCall(PetscInfo(ksp, "Breakdown due to zero inner product\n"));
 85:       break;
 86:     }
 87:     alpha = rho / d1;                           /*   a <- rho / (v,rp)  */
 88:     PetscCall(VecWAXPY(S, -alpha, V, R));       /*   s <- r - a v       */
 89:     PetscCall(KSP_PCApplyBAorAB(ksp, S, T, R)); /*   t <- K s    */
 90:     PetscCall(VecDotNorm2(S, T, &d1, &d2));
 91:     if (d2 == 0.0) {
 92:       /* t is 0.  if s is 0, then alpha v == r, and hence alpha p
 93:          may be our solution.  Give it a try? */
 94:       PetscCall(VecDot(S, S, &d1));
 95:       if (d1 != 0.0) {
 96:         PetscCheck(!ksp->errorifnotconverged, PetscObjectComm((PetscObject)ksp), PETSC_ERR_NOT_CONVERGED, "KSPSolve has failed due to singular preconditioned operator");
 97:         ksp->reason = KSP_DIVERGED_BREAKDOWN;
 98:         PetscCall(PetscInfo(ksp, "Failed due to singular preconditioned operator\n"));
 99:         break;
100:       }
101:       PetscCall(VecAXPY(X, alpha, P)); /*   x <- x + a p       */
102:       PetscCall(PetscObjectSAWsTakeAccess((PetscObject)ksp));
103:       ksp->its++;
104:       ksp->rnorm  = 0.0;
105:       ksp->reason = KSP_CONVERGED_RTOL;
106:       PetscCall(PetscObjectSAWsGrantAccess((PetscObject)ksp));
107:       PetscCall(KSPLogResidualHistory(ksp, dp));
108:       PetscCall(KSPMonitor(ksp, i + 1, 0.0));
109:       break;
110:     }
111:     omega = d1 / d2;                                    /*   w <- (t's) / (t't) */
112:     PetscCall(VecAXPBYPCZ(X, alpha, omega, 1.0, P, S)); /* x <- alpha * p + omega * s + x */
113:     PetscCall(VecWAXPY(R, -omega, T, S));               /*   r <- s - w t       */
114:     if (ksp->normtype != KSP_NORM_NONE && ksp->chknorm < i + 2) {
115:       PetscCall(VecNorm(R, NORM_2, &dp));
116:       KSPCheckNorm(ksp, dp);
117:     }

119:     rhoold   = rho;
120:     omegaold = omega;

122:     PetscCall(PetscObjectSAWsTakeAccess((PetscObject)ksp));
123:     ksp->its++;
124:     ksp->rnorm = dp;
125:     PetscCall(PetscObjectSAWsGrantAccess((PetscObject)ksp));
126:     PetscCall(KSPLogResidualHistory(ksp, dp));
127:     PetscCall(KSPMonitor(ksp, i + 1, dp));
128:     PetscCall((*ksp->converged)(ksp, i + 1, dp, &ksp->reason, ksp->cnvP));
129:     if (ksp->reason) break;
130:     if (rho == 0.0) {
131:       PetscCheck(!ksp->errorifnotconverged, PetscObjectComm((PetscObject)ksp), PETSC_ERR_NOT_CONVERGED, "KSPSolve breakdown due to zero inner product");
132:       ksp->reason = KSP_DIVERGED_BREAKDOWN;
133:       PetscCall(PetscInfo(ksp, "Breakdown due to zero rho inner product\n"));
134:       break;
135:     }
136:     i++;
137:   } while (i < ksp->max_it);

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

141:   PetscCall(KSPUnwindPreconditioner(ksp, X, T));
142:   if (bcgs->guess) PetscCall(VecAXPY(X, 1.0, bcgs->guess));
143:   PetscFunctionReturn(PETSC_SUCCESS);
144: }

146: PetscErrorCode KSPBuildSolution_BCGS(KSP ksp, Vec v, Vec *V)
147: {
148:   KSP_BCGS *bcgs = (KSP_BCGS *)ksp->data;

150:   PetscFunctionBegin;
151:   if (ksp->pc_side == PC_RIGHT) {
152:     if (v) {
153:       PetscCall(KSP_PCApply(ksp, ksp->vec_sol, v));
154:       if (bcgs->guess) PetscCall(VecAXPY(v, 1.0, bcgs->guess));
155:       *V = v;
156:     } else SETERRQ(PetscObjectComm((PetscObject)ksp), PETSC_ERR_SUP, "Not working with right preconditioner");
157:   } else {
158:     if (v) {
159:       PetscCall(VecCopy(ksp->vec_sol, v));
160:       *V = v;
161:     } else *V = ksp->vec_sol;
162:   }
163:   PetscFunctionReturn(PETSC_SUCCESS);
164: }

166: PetscErrorCode KSPReset_BCGS(KSP ksp)
167: {
168:   KSP_BCGS *cg = (KSP_BCGS *)ksp->data;

170:   PetscFunctionBegin;
171:   PetscCall(VecDestroy(&cg->guess));
172:   PetscFunctionReturn(PETSC_SUCCESS);
173: }

175: PetscErrorCode KSPDestroy_BCGS(KSP ksp)
176: {
177:   PetscFunctionBegin;
178:   PetscCall(KSPReset_BCGS(ksp));
179:   PetscCall(KSPDestroyDefault(ksp));
180:   PetscFunctionReturn(PETSC_SUCCESS);
181: }

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

186:    Level: beginner

188:    Notes:
189:    Supports left and right preconditioning but not symmetric

191:    See `KSPBCGSL` for additional stabilization

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

195:    Reference:
196: .  * - van der Vorst, SIAM J. Sci. Stat. Comput., 1992.

198: .seealso: [](ch_ksp), `KSPFBCGS`, `KSPFBCGSR`, `KSPPIPEBCGS`, `KSPBCGSL`, `KSPCreate()`, `KSPSetType()`, `KSPType`, `KSP`, `KSPBICG`, `KSPBCGSL`, `KSPFBICG`, `KSPQMRCGS`, `KSPSetPCSide()`
199: M*/
200: PETSC_EXTERN PetscErrorCode KSPCreate_BCGS(KSP ksp)
201: {
202:   KSP_BCGS *bcgs;

204:   PetscFunctionBegin;
205:   PetscCall(PetscNew(&bcgs));

207:   ksp->data                = bcgs;
208:   ksp->ops->setup          = KSPSetUp_BCGS;
209:   ksp->ops->solve          = KSPSolve_BCGS;
210:   ksp->ops->destroy        = KSPDestroy_BCGS;
211:   ksp->ops->reset          = KSPReset_BCGS;
212:   ksp->ops->buildsolution  = KSPBuildSolution_BCGS;
213:   ksp->ops->buildresidual  = KSPBuildResidualDefault;
214:   ksp->ops->setfromoptions = KSPSetFromOptions_BCGS;

216:   PetscCall(KSPSetSupportedNorm(ksp, KSP_NORM_PRECONDITIONED, PC_LEFT, 3));
217:   PetscCall(KSPSetSupportedNorm(ksp, KSP_NORM_UNPRECONDITIONED, PC_RIGHT, 2));
218:   PetscCall(KSPSetSupportedNorm(ksp, KSP_NORM_NONE, PC_LEFT, 1));
219:   PetscCall(KSPSetSupportedNorm(ksp, KSP_NORM_NONE, PC_RIGHT, 1));
220:   PetscFunctionReturn(PETSC_SUCCESS);
221: }