Date: 2013-07-02T14:48:23+00:00

Actual source code: symmlq.c
petsc-3.4.2 2013-07-02

      2: #include <petsc-private/kspimpl.h>

      4: typedef struct {
      5:   PetscReal haptol;
      6: } KSP_SYMMLQ;

     10: PetscErrorCode KSPSetUp_SYMMLQ(KSP ksp)
     11: {

     15:   KSPSetWorkVecs(ksp,9);
     16:   return(0);
     17: }

     21: PetscErrorCode  KSPSolve_SYMMLQ(KSP ksp)
     22: {
     24:   PetscInt       i;
     25:   PetscScalar    alpha,beta,ibeta,betaold,beta1,ceta = 0,ceta_oold = 0.0, ceta_old = 0.0,ceta_bar;
     26:   PetscScalar    c  = 1.0,cold=1.0,s=0.0,sold=0.0,coold,soold,rho0,rho1,rho2,rho3;
     27:   PetscScalar    dp = 0.0;
     28:   PetscReal      np,s_prod;
     29:   Vec            X,B,R,Z,U,V,W,UOLD,VOLD,Wbar;
     30:   Mat            Amat,Pmat;
     31:   MatStructure   pflag;
     32:   KSP_SYMMLQ     *symmlq = (KSP_SYMMLQ*)ksp->data;
     33:   PetscBool      diagonalscale;

     36:   PCGetDiagonalScale(ksp->pc,&diagonalscale);
     37:   if (diagonalscale) SETERRQ1(PetscObjectComm((PetscObject)ksp),PETSC_ERR_SUP,"Krylov method %s does not support diagonal scaling",((PetscObject)ksp)->type_name);

     39:   X    = ksp->vec_sol;
     40:   B    = ksp->vec_rhs;
     41:   R    = ksp->work[0];
     42:   Z    = ksp->work[1];
     43:   U    = ksp->work[2];
     44:   V    = ksp->work[3];
     45:   W    = ksp->work[4];
     46:   UOLD = ksp->work[5];
     47:   VOLD = ksp->work[6];
     48:   Wbar = ksp->work[7];

     50:   PCGetOperators(ksp->pc,&Amat,&Pmat,&pflag);

     52:   ksp->its = 0;

     54:   VecSet(UOLD,0.0);           /* u_old <- zeros;  */
     55:   VecCopy(UOLD,VOLD);          /* v_old <- u_old;  */
     56:   VecCopy(UOLD,W);             /* w     <- u_old;  */
     57:   VecCopy(UOLD,Wbar);          /* w_bar <- u_old;  */
     58:   if (!ksp->guess_zero) {
     59:     KSP_MatMult(ksp,Amat,X,R); /*     r <- b - A*x */
     60:     VecAYPX(R,-1.0,B);
     61:   } else {
     62:     VecCopy(B,R);              /*     r <- b (x is 0) */
     63:   }

     65:   KSP_PCApply(ksp,R,Z); /* z  <- B*r       */
     66:   VecDot(R,Z,&dp);             /* dp = r'*z;      */
     67:   if (PetscAbsScalar(dp) < symmlq->haptol) {
     68:     PetscInfo2(ksp,"Detected happy breakdown %G tolerance %G\n",PetscAbsScalar(dp),symmlq->haptol);
     69:     ksp->rnorm  = 0.0;  /* what should we really put here? */
     70:     ksp->reason = KSP_CONVERGED_HAPPY_BREAKDOWN;  /* bugfix proposed by Lourens (lourens.vanzanen@shell.com) */
     71:     return(0);
     72:   }

     74: #if !defined(PETSC_USE_COMPLEX)
     75:   if (dp < 0.0) {
     76:     ksp->reason = KSP_DIVERGED_INDEFINITE_PC;
     77:     return(0);
     78:   }
     79: #endif
     80:   dp     = PetscSqrtScalar(dp);
     81:   beta   = dp;                         /*  beta <- sqrt(r'*z)  */
     82:   beta1  = beta;
     83:   s_prod = PetscAbsScalar(beta1);

     85:   VecCopy(R,V); /* v <- r; */
     86:   VecCopy(Z,U); /* u <- z; */
     87:   ibeta = 1.0 / beta;
     88:   VecScale(V,ibeta);    /* v <- ibeta*v; */
     89:   VecScale(U,ibeta);    /* u <- ibeta*u; */
     90:   VecCopy(U,Wbar);       /* w_bar <- u;   */
     91:   VecNorm(Z,NORM_2,&np);     /*   np <- ||z||        */
     92:   KSPLogResidualHistory(ksp,np);
     93:   KSPMonitor(ksp,0,np);
     94:   ksp->rnorm = np;
     95:   (*ksp->converged)(ksp,0,np,&ksp->reason,ksp->cnvP); /* test for convergence */
     96:   if (ksp->reason) return(0);

     98:   i = 0; ceta = 0.;
     99:   do {
    100:     ksp->its = i+1;

    102:     /*    Update    */
    103:     if (ksp->its > 1) {
    104:       VecCopy(V,VOLD);  /* v_old <- v; */
    105:       VecCopy(U,UOLD);  /* u_old <- u; */

    107:       VecCopy(R,V);
    108:       VecScale(V,1.0/beta); /* v <- ibeta*r; */
    109:       VecCopy(Z,U);
    110:       VecScale(U,1.0/beta); /* u <- ibeta*z; */

    112:       VecCopy(Wbar,W);
    113:       VecScale(W,c);
    114:       VecAXPY(W,s,U);   /* w  <- c*w_bar + s*u;    (w_k) */
    115:       VecScale(Wbar,-s);
    116:       VecAXPY(Wbar,c,U); /* w_bar <- -s*w_bar + c*u; (w_bar_(k+1)) */
    117:       VecAXPY(X,ceta,W); /* x <- x + ceta * w;       (xL_k)  */

    119:       ceta_oold = ceta_old;
    120:       ceta_old  = ceta;
    121:     }

    123:     /*   Lanczos  */
    124:     KSP_MatMult(ksp,Amat,U,R);   /*  r     <- Amat*u; */
    125:     VecDot(U,R,&alpha);          /*  alpha <- u'*r;   */
    126:     KSP_PCApply(ksp,R,Z); /*      z <- B*r;    */

    128:     VecAXPY(R,-alpha,V);   /*  r <- r - alpha* v;  */
    129:     VecAXPY(Z,-alpha,U);   /*  z <- z - alpha* u;  */
    130:     VecAXPY(R,-beta,VOLD); /*  r <- r - beta * v_old; */
    131:     VecAXPY(Z,-beta,UOLD); /*  z <- z - beta * u_old; */
    132:     betaold = beta;                                /* beta_k                  */
    133:     VecDot(R,Z,&dp);       /* dp <- r'*z;             */
    134:     if (PetscAbsScalar(dp) < symmlq->haptol) {
    135:       PetscInfo2(ksp,"Detected happy breakdown %G tolerance %G\n",PetscAbsScalar(dp),symmlq->haptol);
    136:       dp   = 0.0;
    137:     }

    139: #if !defined(PETSC_USE_COMPLEX)
    140:     if (dp < 0.0) {
    141:       ksp->reason = KSP_DIVERGED_INDEFINITE_PC;
    142:       break;
    143:     }
    144: #endif
    145:     beta = PetscSqrtScalar(dp);                    /*  beta = sqrt(dp); */

    147:     /*    QR factorization    */
    148:     coold = cold; cold = c; soold = sold; sold = s;
    149:     rho0  = cold * alpha - coold * sold * betaold;   /* gamma_bar */
    150:     rho1  = PetscSqrtScalar(rho0*rho0 + beta*beta);  /* gamma     */
    151:     rho2  = sold * alpha + coold * cold * betaold;   /* delta     */
    152:     rho3  = soold * betaold;                         /* epsilon   */

    154:     /* Givens rotation: [c -s; s c] (different from the Reference!) */
    155:     c = rho0 / rho1; s = beta / rho1;

    157:     if (ksp->its==1) ceta = beta1/rho1;
    158:     else ceta = -(rho2*ceta_old + rho3*ceta_oold)/rho1;

    160:     s_prod = s_prod*PetscAbsScalar(s);
    161:     if (c == 0.0) np = s_prod*1.e16;
    162:     else np = s_prod/PetscAbsScalar(c);       /* residual norm for xc_k (CGNORM) */

    164:     ksp->rnorm = np;
    165:     KSPLogResidualHistory(ksp,np);
    166:     KSPMonitor(ksp,i+1,np);
    167:     (*ksp->converged)(ksp,i+1,np,&ksp->reason,ksp->cnvP); /* test for convergence */
    168:     if (ksp->reason) break;
    169:     i++;
    170:   } while (i<ksp->max_it);

    172:   /* move to the CG point: xc_(k+1) */
    173:   if (c == 0.0) ceta_bar = ceta*1.e15;
    174:   else ceta_bar = ceta/c;

    176:   VecAXPY(X,ceta_bar,Wbar); /* x <- x + ceta_bar*w_bar */

    178:   if (i >= ksp->max_it) ksp->reason = KSP_DIVERGED_ITS;
    179:   return(0);
    180: }

    182: /*MC
    183:      KSPSYMMLQ -  This code implements the SYMMLQ method.

    185:    Options Database Keys:
    186: .   see KSPSolve()

    188:    Level: beginner

    190:    Notes: The operator and the preconditioner must be symmetric for this method. The
    191:           preconditioner must be POSITIVE-DEFINITE.

    193:           Supports only left preconditioning.

    195:    Reference: Paige & Saunders, 1975.

    197: .seealso: KSPCreate(), KSPSetType(), KSPType (for list of available types), KSP
    198: M*/
    201: PETSC_EXTERN PetscErrorCode KSPCreate_SYMMLQ(KSP ksp)
    202: {
    203:   KSP_SYMMLQ     *symmlq;

    207:   KSPSetSupportedNorm(ksp,KSP_NORM_PRECONDITIONED,PC_LEFT,2);

    209:   PetscNewLog(ksp,KSP_SYMMLQ,&symmlq);
    210:   symmlq->haptol = 1.e-18;
    211:   ksp->data      = (void*)symmlq;

    213:   /*
    214:        Sets the functions that are associated with this data structure
    215:        (in C++ this is the same as defining virtual functions)
    216:   */
    217:   ksp->ops->setup          = KSPSetUp_SYMMLQ;
    218:   ksp->ops->solve          = KSPSolve_SYMMLQ;
    219:   ksp->ops->destroy        = KSPDestroyDefault;
    220:   ksp->ops->setfromoptions = 0;
    221:   ksp->ops->buildsolution  = KSPBuildSolutionDefault;
    222:   ksp->ops->buildresidual  = KSPBuildResidualDefault;
    223:   return(0);
    224: }