Actual source code: tfqmr.c
petsc-3.10.5 2019-03-28
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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:   PetscObjectSAWsTakeAccess((PetscObject)ksp);
     42:   ksp->rnorm = dp;
     43:   ksp->its   = 0;
     44:   PetscObjectSAWsGrantAccess((PetscObject)ksp);
     45:   KSPMonitor(ksp,0,dp);
     46:   (*ksp->converged)(ksp,0,dp,&ksp->reason,ksp->cnvP);
     47:   if (ksp->reason) return(0);

     49:   /* Make the initial Rp == R */
     50:   VecCopy(R,RP);

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

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

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

     91:       dpest      = PetscSqrtReal(m + 1.0) * tau;
     92:       PetscObjectSAWsTakeAccess((PetscObject)ksp);
     93:       ksp->rnorm = dpest;
     94:       PetscObjectSAWsGrantAccess((PetscObject)ksp);
     95:       KSPLogResidualHistory(ksp,dpest);
     96:       KSPMonitor(ksp,i+1,dpest);
     97:       (*ksp->converged)(ksp,i+1,dpest,&ksp->reason,ksp->cnvP);
     98:       if (ksp->reason) break;

    100:       etaold = eta;
    101:       psiold = psi;
    102:     }
    103:     if (ksp->reason) break;

    105:     VecDot(R,RP,&rho);        /* rho <- (r,rp)       */
    106:     b    = rho / rhoold;                            /* b <- rho / rhoold   */
    107:     VecWAXPY(U,b,Q,R);       /* u <- r + b q        */
    108:     VecAXPY(Q,b,P);
    109:     VecWAXPY(P,b,Q,U);       /* p <- u + b(q + b p) */
    110:     KSP_PCApplyBAorAB(ksp,P,V,Q); /* v <- K p  */

    112:     rhoold = rho;
    113:     dpold  = dp;

    115:     i++;
    116:   } while (i<ksp->max_it);
    117:   if (i >= ksp->max_it) ksp->reason = KSP_DIVERGED_ITS;

    119:   KSPUnwindPreconditioner(ksp,X,T);
    120:   return(0);
    121: }

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

    126:    Options Database Keys:
    127: .   see KSPSolve()

    129:    Level: beginner

    131:    Notes:
    132:     Supports left and right preconditioning, but not symmetric

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

    138:    References:
    139: .   1. -  Freund, 1993

    141: .seealso: KSPCreate(), KSPSetType(), KSPType (for list of available types), KSP, KSPTCQMR
    142: M*/
    143: PETSC_EXTERN PetscErrorCode KSPCreate_TFQMR(KSP ksp)
    144: {

    148:   KSPSetSupportedNorm(ksp,KSP_NORM_PRECONDITIONED,PC_LEFT,3);
    149:   KSPSetSupportedNorm(ksp,KSP_NORM_UNPRECONDITIONED,PC_RIGHT,2);

    151:   ksp->data                = (void*)0;
    152:   ksp->ops->setup          = KSPSetUp_TFQMR;
    153:   ksp->ops->solve          = KSPSolve_TFQMR;
    154:   ksp->ops->destroy        = KSPDestroyDefault;
    155:   ksp->ops->buildsolution  = KSPBuildSolutionDefault;
    156:   ksp->ops->buildresidual  = KSPBuildResidualDefault;
    157:   ksp->ops->setfromoptions = 0;
    158:   ksp->ops->view           = 0;
    159:   return(0);
    160: }