Actual source code: cgs.c


  2: /*
  3:     Note that for the complex numbers version, the VecDot() arguments
  4:     within the code MUST remain in the order given for correct computation
  5:     of inner products.
  6: */
  7: #include <petsc/private/kspimpl.h>

  9: static PetscErrorCode KSPSetUp_CGS(KSP ksp)
 10: {
 11:   KSPSetWorkVecs(ksp, 7);
 12:   return 0;
 13: }

 15: static PetscErrorCode KSPSolve_CGS(KSP ksp)
 16: {
 17:   PetscInt    i;
 18:   PetscScalar rho, rhoold, a, s, b;
 19:   Vec         X, B, V, P, R, RP, T, Q, U, AUQ;
 20:   PetscReal   dp = 0.0;
 21:   PetscBool   diagonalscale;

 23:   /* not sure what residual norm it does use, should use for right preconditioning */

 25:   PCGetDiagonalScale(ksp->pc, &diagonalscale);

 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:   Q   = ksp->work[4];
 35:   P   = ksp->work[5];
 36:   U   = ksp->work[6];
 37:   AUQ = V;

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

 42:   /* Test for nothing to do */
 43:   if (ksp->normtype != KSP_NORM_NONE) {
 44:     VecNorm(R, NORM_2, &dp);
 45:     KSPCheckNorm(ksp, dp);
 46:     if (ksp->normtype == KSP_NORM_NATURAL) dp *= dp;
 47:   } else dp = 0.0;

 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) return 0;

 58:   /* Make the initial Rp == R */
 59:   VecCopy(R, RP);
 60:   /*  added for Fidap */
 61:   /* Penalize Startup - Isaac Hasbani Trick for CGS
 62:      Since most initial conditions result in a mostly 0 residual,
 63:      we change all the 0 values in the vector RP to the maximum.
 64:   */
 65:   if (ksp->normtype == KSP_NORM_NATURAL) {
 66:     PetscReal    vr0max;
 67:     PetscScalar *tmp_RP = NULL;
 68:     PetscInt     numnp = 0, *max_pos = NULL;
 69:     VecMax(RP, max_pos, &vr0max);
 70:     VecGetArray(RP, &tmp_RP);
 71:     VecGetLocalSize(RP, &numnp);
 72:     for (i = 0; i < numnp; i++) {
 73:       if (tmp_RP[i] == 0.0) tmp_RP[i] = vr0max;
 74:     }
 75:     VecRestoreArray(RP, &tmp_RP);
 76:   }
 77:   /*  end of addition for Fidap */

 79:   /* Set the initial conditions */
 80:   VecDot(R, RP, &rhoold); /* rhoold = (r,rp)      */
 81:   VecCopy(R, U);
 82:   VecCopy(R, P);
 83:   KSP_PCApplyBAorAB(ksp, P, V, T);

 85:   i = 0;
 86:   do {
 87:     VecDot(V, RP, &s); /* s <- (v,rp)          */
 88:     KSPCheckDot(ksp, s);
 89:     a = rhoold / s;                    /* a <- rho / s         */
 90:     VecWAXPY(Q, -a, V, U);  /* q <- u - a v         */
 91:     VecWAXPY(T, 1.0, U, Q); /* t <- u + q           */
 92:     VecAXPY(X, a, T);       /* x <- x + a (u + q)   */
 93:     KSP_PCApplyBAorAB(ksp, T, AUQ, U);
 94:     VecAXPY(R, -a, AUQ); /* r <- r - a K (u + q) */
 95:     VecDot(R, RP, &rho); /* rho <- (r,rp)        */
 96:     KSPCheckDot(ksp, rho);
 97:     if (ksp->normtype == KSP_NORM_NATURAL) {
 98:       dp = PetscAbsScalar(rho);
 99:     } else if (ksp->normtype != KSP_NORM_NONE) {
100:       VecNorm(R, NORM_2, &dp);
101:       KSPCheckNorm(ksp, dp);
102:     } else dp = 0.0;

104:     PetscObjectSAWsTakeAccess((PetscObject)ksp);
105:     ksp->its++;
106:     ksp->rnorm = dp;
107:     PetscObjectSAWsGrantAccess((PetscObject)ksp);
108:     KSPLogResidualHistory(ksp, dp);
109:     KSPMonitor(ksp, i + 1, dp);
110:     (*ksp->converged)(ksp, i + 1, dp, &ksp->reason, ksp->cnvP);
111:     if (ksp->reason) break;

113:     b = rho / rhoold;                /* b <- rho / rhoold    */
114:     VecWAXPY(U, b, Q, R); /* u <- r + b q         */
115:     VecAXPY(Q, b, P);
116:     VecWAXPY(P, b, Q, U);            /* p <- u + b(q + b p)  */
117:     KSP_PCApplyBAorAB(ksp, P, V, Q); /* v <- K p    */
118:     rhoold = rho;
119:     i++;
120:   } while (i < ksp->max_it);
121:   if (i >= ksp->max_it) ksp->reason = KSP_DIVERGED_ITS;

123:   KSPUnwindPreconditioner(ksp, X, T);
124:   return 0;
125: }

127: /*MC
128:      KSPCGS - This code implements the CGS (Conjugate Gradient Squared) method.

130:    Level: beginner

132:    Notes:
133:    Does not require a symmetric matrix. Does not apply transpose of the matrix.

135:    Supports left and right preconditioning, but not symmetric.

137:    Developer Note:
138:    Has this weird support for doing the convergence test with the natural norm, I assume this works only with
139:    no preconditioning and symmetric positive definite operator.

141:    References:
142: .  * - Sonneveld, 1989.

144: .seealso: [](chapter_ksp), `KSPCreate()`, `KSPSetType()`, `KSPType`, `KSP`, `KSPBCGS`, `KSPSetPCSide()`
145: M*/
146: PETSC_EXTERN PetscErrorCode KSPCreate_CGS(KSP ksp)
147: {
148:   ksp->data = (void *)0;

150:   KSPSetSupportedNorm(ksp, KSP_NORM_PRECONDITIONED, PC_LEFT, 3);
151:   KSPSetSupportedNorm(ksp, KSP_NORM_UNPRECONDITIONED, PC_RIGHT, 2);
152:   KSPSetSupportedNorm(ksp, KSP_NORM_NATURAL, PC_LEFT, 2);
153:   KSPSetSupportedNorm(ksp, KSP_NORM_NATURAL, PC_RIGHT, 2);
154:   KSPSetSupportedNorm(ksp, KSP_NORM_NONE, PC_LEFT, 1);
155:   KSPSetSupportedNorm(ksp, KSP_NORM_NONE, PC_RIGHT, 1);

157:   ksp->ops->setup          = KSPSetUp_CGS;
158:   ksp->ops->solve          = KSPSolve_CGS;
159:   ksp->ops->destroy        = KSPDestroyDefault;
160:   ksp->ops->buildsolution  = KSPBuildSolutionDefault;
161:   ksp->ops->buildresidual  = KSPBuildResidualDefault;
162:   ksp->ops->setfromoptions = NULL;
163:   ksp->ops->view           = NULL;
164:   return 0;
165: }