Actual source code: tfqmr.c
petsc-3.15.0 2021-03-30
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      2: #include <petsc/private/kspimpl.h>

      4: static PetscErrorCode KSPSetUp_TFQMR(KSP ksp)
      5: {

      9:   if (ksp->pc_side == PC_SYMMETRIC) SETERRQ(PetscObjectComm((PetscObject)ksp),PETSC_ERR_SUP,"no symmetric preconditioning for KSPTFQMR");
     10:   KSPSetWorkVecs(ksp,9);
     11:   return(0);
     12: }

     14: static PetscErrorCode  KSPSolve_TFQMR(KSP ksp)
     15: {
     17:   PetscInt       i,m;
     18:   PetscScalar    rho,rhoold,a,s,b,eta,etaold,psiold,cf;
     19:   PetscReal      dp,dpold,w,dpest,tau,psi,cm;
     20:   Vec            X,B,V,P,R,RP,T,T1,Q,U,D,AUQ;

     23:   X   = ksp->vec_sol;
     24:   B   = ksp->vec_rhs;
     25:   R   = ksp->work[0];
     26:   RP  = ksp->work[1];
     27:   V   = ksp->work[2];
     28:   T   = ksp->work[3];
     29:   Q   = ksp->work[4];
     30:   P   = ksp->work[5];
     31:   U   = ksp->work[6];
     32:   D   = ksp->work[7];
     33:   T1  = ksp->work[8];
     34:   AUQ = V;

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

     39:   /* Test for nothing to do */
     40:   VecNorm(R,NORM_2,&dp);
     41:   KSPCheckNorm(ksp,dp);
     42:   PetscObjectSAWsTakeAccess((PetscObject)ksp);
     43:   if (ksp->normtype != KSP_NORM_NONE) ksp->rnorm = dp;
     44:   else ksp->rnorm = 0.0;
     45:   ksp->its = 0;
     46:   PetscObjectSAWsGrantAccess((PetscObject)ksp);
     47:   KSPMonitor(ksp,0,ksp->rnorm);
     48:   (*ksp->converged)(ksp,0,ksp->rnorm,&ksp->reason,ksp->cnvP);
     49:   if (ksp->reason) return(0);

     51:   /* Make the initial Rp == R */
     52:   VecCopy(R,RP);

     54:   /* Set the initial conditions */
     55:   etaold = 0.0;
     56:   psiold = 0.0;
     57:   tau    = dp;
     58:   dpold  = dp;

     60:   VecDot(R,RP,&rhoold);       /* rhoold = (r,rp)     */
     61:   VecCopy(R,U);
     62:   VecCopy(R,P);
     63:   KSP_PCApplyBAorAB(ksp,P,V,T);
     64:   VecSet(D,0.0);

     66:   i=0;
     67:   do {
     68:     PetscObjectSAWsTakeAccess((PetscObject)ksp);
     69:     ksp->its++;
     70:     PetscObjectSAWsGrantAccess((PetscObject)ksp);
     71:     VecDot(V,RP,&s);          /* s <- (v,rp)          */
     72:     KSPCheckDot(ksp,s);
     73:     a    = rhoold / s;                              /* a <- rho / s         */
     74:     VecWAXPY(Q,-a,V,U);  /* q <- u - a v         */
     75:     VecWAXPY(T,1.0,U,Q);     /* t <- u + q           */
     76:     KSP_PCApplyBAorAB(ksp,T,AUQ,T1);
     77:     VecAXPY(R,-a,AUQ);      /* r <- r - a K (u + q) */
     78:     VecNorm(R,NORM_2,&dp);
     79:     KSPCheckNorm(ksp,dp);
     80:     for (m=0; m<2; m++) {
     81:       if (!m) w = PetscSqrtReal(dp*dpold);
     82:       else w = dp;
     83:       psi = w / tau;
     84:       cm  = 1.0 / PetscSqrtReal(1.0 + psi * psi);
     85:       tau = tau * psi * cm;
     86:       eta = cm * cm * a;
     87:       cf  = psiold * psiold * etaold / a;
     88:       if (!m) {
     89:         VecAYPX(D,cf,U);
     90:       } else {
     91:         VecAYPX(D,cf,Q);
     92:       }
     93:       VecAXPY(X,eta,D);

     95:       dpest = PetscSqrtReal(m + 1.0) * tau;
     96:       PetscObjectSAWsTakeAccess((PetscObject)ksp);
     97:       if (ksp->normtype != KSP_NORM_NONE) ksp->rnorm = dpest;
     98:       else ksp->rnorm = 0.0;
     99:       PetscObjectSAWsGrantAccess((PetscObject)ksp);
    100:       KSPLogResidualHistory(ksp,ksp->rnorm);
    101:       KSPMonitor(ksp,i+1,ksp->rnorm);
    102:       (*ksp->converged)(ksp,i+1,ksp->rnorm,&ksp->reason,ksp->cnvP);
    103:       if (ksp->reason) break;

    105:       etaold = eta;
    106:       psiold = psi;
    107:     }
    108:     if (ksp->reason) break;

    110:     VecDot(R,RP,&rho);        /* rho <- (r,rp)       */
    111:     b    = rho / rhoold;                            /* b <- rho / rhoold   */
    112:     VecWAXPY(U,b,Q,R);       /* u <- r + b q        */
    113:     VecAXPY(Q,b,P);
    114:     VecWAXPY(P,b,Q,U);       /* p <- u + b(q + b p) */
    115:     KSP_PCApplyBAorAB(ksp,P,V,Q); /* v <- K p  */

    117:     rhoold = rho;
    118:     dpold  = dp;

    120:     i++;
    121:   } while (i<ksp->max_it);
    122:   if (i >= ksp->max_it) ksp->reason = KSP_DIVERGED_ITS;

    124:   KSPUnwindPreconditioner(ksp,X,T);
    125:   return(0);
    126: }

    128: /*MC
    129:      KSPTFQMR - A transpose free QMR (quasi minimal residual),

    131:    Options Database Keys:
    132: .   see KSPSolve()

    134:    Level: beginner

    136:    Notes:
    137:     Supports left and right preconditioning, but not symmetric

    139:           The "residual norm" computed in this algorithm is actually just an upper bound on the actual residual norm.
    140:           That is for left preconditioning it is a bound on the preconditioned residual and for right preconditioning
    141:           it is a bound on the true residual.

    143:    References:
    144: .   1. -  Freund, 1993

    146: .seealso: KSPCreate(), KSPSetType(), KSPType (for list of available types), KSP, KSPTCQMR
    147: M*/
    148: PETSC_EXTERN PetscErrorCode KSPCreate_TFQMR(KSP ksp)
    149: {

    153:   KSPSetSupportedNorm(ksp,KSP_NORM_PRECONDITIONED,PC_LEFT,3);
    154:   KSPSetSupportedNorm(ksp,KSP_NORM_UNPRECONDITIONED,PC_RIGHT,2);
    155:   KSPSetSupportedNorm(ksp,KSP_NORM_NONE,PC_LEFT,1);
    156:   KSPSetSupportedNorm(ksp,KSP_NORM_NONE,PC_RIGHT,1);

    158:   ksp->data                = (void*)0;
    159:   ksp->ops->setup          = KSPSetUp_TFQMR;
    160:   ksp->ops->solve          = KSPSolve_TFQMR;
    161:   ksp->ops->destroy        = KSPDestroyDefault;
    162:   ksp->ops->buildsolution  = KSPBuildSolutionDefault;
    163:   ksp->ops->buildresidual  = KSPBuildResidualDefault;
    164:   ksp->ops->setfromoptions = NULL;
    165:   ksp->ops->view           = NULL;
    166:   return(0);
    167: }