Actual source code: bcgs.c

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

182: /*MC
183:    KSPBCGS - Implements the BiCGStab (Stabilized version of Biconjugate Gradient) method {cite}`vorst92`

185:    Level: beginner

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

190:    See `KSPBCGSL` for additional stabilization

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

194: .seealso: [](ch_ksp), `KSPFBCGS`, `KSPFBCGSR`, `KSPPIPEBCGS`, `KSPBCGSL`, `KSPCreate()`, `KSPSetType()`, `KSPType`, `KSP`, `KSPBICG`, `KSPBCGSL`, `KSPFBICG`, `KSPQMRCGS`, `KSPSetPCSide()`
195: M*/
196: PETSC_EXTERN PetscErrorCode KSPCreate_BCGS(KSP ksp)
197: {
198:   KSP_BCGS *bcgs;

200:   PetscFunctionBegin;
201:   PetscCall(PetscNew(&bcgs));

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

212:   PetscCall(KSPSetSupportedNorm(ksp, KSP_NORM_PRECONDITIONED, PC_LEFT, 3));
213:   PetscCall(KSPSetSupportedNorm(ksp, KSP_NORM_UNPRECONDITIONED, PC_RIGHT, 2));
214:   PetscCall(KSPSetSupportedNorm(ksp, KSP_NORM_NONE, PC_LEFT, 1));
215:   PetscCall(KSPSetSupportedNorm(ksp, KSP_NORM_NONE, PC_RIGHT, 1));
216:   PetscFunctionReturn(PETSC_SUCCESS);
217: }