xref: /petsc/src/snes/impls/ngmres/snesngmres.c (revision 8cc058d9cd56c1ccb3be12a47760ddfc446aaffc)

#include <../src/snes/impls/ngmres/snesngmres.h> /*I "petscsnes.h" I*/
#include <petscblaslapack.h>

const char *const SNESNGMRESRestartTypes[] = {"NONE","PERIODIC","DIFFERENCE","SNESNGMRESRestartType","SNES_NGMRES_RESTART_",0};
const char *const SNESNGMRESSelectTypes[] = {"NONE","DIFFERENCE","LINESEARCH","SNESNGMRESSelectType","SNES_NGMRES_SELECT_",0};

#undef __FUNCT__
#define __FUNCT__ "SNESReset_NGMRES"
PetscErrorCode SNESReset_NGMRES(SNES snes)
{
  SNES_NGMRES    *ngmres = (SNES_NGMRES*) snes->data;
  PetscErrorCode ierr;

  PetscFunctionBegin;
  ierr = VecDestroyVecs(ngmres->msize,&ngmres->Fdot);CHKERRQ(ierr);
  ierr = VecDestroyVecs(ngmres->msize,&ngmres->Xdot);CHKERRQ(ierr);
  ierr = SNESLineSearchDestroy(&ngmres->additive_linesearch);CHKERRQ(ierr);
  PetscFunctionReturn(0);
}

#undef __FUNCT__
#define __FUNCT__ "SNESDestroy_NGMRES"
PetscErrorCode SNESDestroy_NGMRES(SNES snes)
{
  PetscErrorCode ierr;
  SNES_NGMRES    *ngmres = (SNES_NGMRES*)snes->data;

  PetscFunctionBegin;
  ierr = SNESReset_NGMRES(snes);CHKERRQ(ierr);
  ierr = PetscFree5(ngmres->h,ngmres->beta,ngmres->xi,ngmres->fnorms,ngmres->q);CHKERRQ(ierr);
  ierr = PetscFree(ngmres->s);CHKERRQ(ierr);
  ierr = PetscFree(ngmres->xnorms);CHKERRQ(ierr);
#if PETSC_USE_COMPLEX
  ierr = PetscFree(ngmres->rwork);CHKERRQ(ierr);
#endif
  ierr = PetscFree(ngmres->work);CHKERRQ(ierr);
  ierr = PetscFree(snes->data);CHKERRQ(ierr);
  PetscFunctionReturn(0);
}

#undef __FUNCT__
#define __FUNCT__ "SNESSetUp_NGMRES"
PetscErrorCode SNESSetUp_NGMRES(SNES snes)
{
  SNES_NGMRES    *ngmres = (SNES_NGMRES*) snes->data;
  const char     *optionsprefix;
  PetscInt       msize,hsize;
  PetscErrorCode ierr;

  PetscFunctionBegin;
  ierr = SNESDefaultGetWork(snes,5);CHKERRQ(ierr);
  if (!ngmres->Xdot) {ierr = VecDuplicateVecs(snes->vec_sol,ngmres->msize,&ngmres->Xdot);CHKERRQ(ierr);}
  if (!ngmres->Fdot) {ierr = VecDuplicateVecs(snes->vec_sol,ngmres->msize,&ngmres->Fdot);CHKERRQ(ierr);}
  if (!ngmres->setup_called) {
    msize = ngmres->msize;          /* restart size */
    hsize = msize * msize;

    /* explicit least squares minimization solve */
    ierr = PetscMalloc5(hsize,PetscScalar,&ngmres->h,
                        msize,PetscScalar,&ngmres->beta,
                        msize,PetscScalar,&ngmres->xi,
                        msize,PetscReal, &ngmres->fnorms,
                        hsize,PetscScalar,&ngmres->q);CHKERRQ(ierr);
    if (ngmres->singlereduction) {
      ierr = PetscMalloc(msize*sizeof(PetscReal),&ngmres->xnorms);CHKERRQ(ierr);
    }
    ngmres->nrhs  = 1;
    ngmres->lda   = msize;
    ngmres->ldb   = msize;
    ierr          = PetscMalloc(msize*sizeof(PetscScalar),&ngmres->s);CHKERRQ(ierr);
    ierr          = PetscMemzero(ngmres->h,   hsize*sizeof(PetscScalar));CHKERRQ(ierr);
    ierr          = PetscMemzero(ngmres->q,   hsize*sizeof(PetscScalar));CHKERRQ(ierr);
    ierr          = PetscMemzero(ngmres->xi,  msize*sizeof(PetscScalar));CHKERRQ(ierr);
    ierr          = PetscMemzero(ngmres->beta,msize*sizeof(PetscScalar));CHKERRQ(ierr);
    ngmres->lwork = 12*msize;
#if PETSC_USE_COMPLEX
    ierr = PetscMalloc(sizeof(PetscReal)*ngmres->lwork,&ngmres->rwork);CHKERRQ(ierr);
#endif
    ierr = PetscMalloc(sizeof(PetscScalar)*ngmres->lwork,&ngmres->work);CHKERRQ(ierr);
  }

  /* linesearch setup */
  ierr = SNESGetOptionsPrefix(snes,&optionsprefix);CHKERRQ(ierr);

  if (ngmres->select_type == SNES_NGMRES_SELECT_LINESEARCH) {
    ierr = SNESLineSearchCreate(PetscObjectComm((PetscObject)snes),&ngmres->additive_linesearch);CHKERRQ(ierr);
    ierr = SNESLineSearchSetSNES(ngmres->additive_linesearch,snes);CHKERRQ(ierr);
    ierr = SNESLineSearchSetType(ngmres->additive_linesearch,SNESLINESEARCHL2);CHKERRQ(ierr);
    ierr = SNESLineSearchAppendOptionsPrefix(ngmres->additive_linesearch,"additive_");CHKERRQ(ierr);
    ierr = SNESLineSearchAppendOptionsPrefix(ngmres->additive_linesearch,optionsprefix);CHKERRQ(ierr);
    ierr = SNESLineSearchSetFromOptions(ngmres->additive_linesearch);CHKERRQ(ierr);
  }

  ngmres->setup_called = PETSC_TRUE;
  PetscFunctionReturn(0);
}

#undef __FUNCT__
#define __FUNCT__ "SNESSetFromOptions_NGMRES"
PetscErrorCode SNESSetFromOptions_NGMRES(SNES snes)
{
  SNES_NGMRES    *ngmres = (SNES_NGMRES*) snes->data;
  PetscErrorCode ierr;
  PetscBool      debug;
  SNESLineSearch linesearch;

  PetscFunctionBegin;
  ierr = PetscOptionsHead("SNES NGMRES options");CHKERRQ(ierr);
  ierr = PetscOptionsEnum("-snes_ngmres_select_type","Select type","SNESNGMRESSetSelectType",SNESNGMRESSelectTypes,
                          (PetscEnum)ngmres->select_type,(PetscEnum*)&ngmres->select_type,NULL);CHKERRQ(ierr);
  ierr = PetscOptionsEnum("-snes_ngmres_restart_type","Restart type","SNESNGMRESSetRestartType",SNESNGMRESRestartTypes,
                          (PetscEnum)ngmres->restart_type,(PetscEnum*)&ngmres->restart_type,NULL);CHKERRQ(ierr);
  ierr = PetscOptionsBool("-snes_ngmres_candidate", "Use candidate storage",              "SNES",ngmres->candidate,&ngmres->candidate,NULL);CHKERRQ(ierr);
  ierr = PetscOptionsBool("-snes_ngmres_approxfunc","Linearly approximate the function", "SNES",ngmres->approxfunc,&ngmres->approxfunc,NULL);CHKERRQ(ierr);
  ierr = PetscOptionsInt("-snes_ngmres_m",          "Number of directions",               "SNES",ngmres->msize,&ngmres->msize,NULL);CHKERRQ(ierr);
  ierr = PetscOptionsInt("-snes_ngmres_restart",    "Iterations before forced restart",   "SNES",ngmres->restart_periodic,&ngmres->restart_periodic,NULL);CHKERRQ(ierr);
  ierr = PetscOptionsInt("-snes_ngmres_restart_it", "Tolerance iterations before restart","SNES",ngmres->restart_it,&ngmres->restart_it,NULL);CHKERRQ(ierr);
  ierr = PetscOptionsBool("-snes_ngmres_monitor",   "Monitor actions of NGMRES",          "SNES",ngmres->monitor ? PETSC_TRUE : PETSC_FALSE,&debug,NULL);CHKERRQ(ierr);
  if (debug) {
    ngmres->monitor = PETSC_VIEWER_STDOUT_(PetscObjectComm((PetscObject)snes));CHKERRQ(ierr);
  }
  ierr = PetscOptionsReal("-snes_ngmres_gammaA",    "Residual selection constant",   "SNES",ngmres->gammaA,&ngmres->gammaA,NULL);CHKERRQ(ierr);
  ierr = PetscOptionsReal("-snes_ngmres_gammaC",    "Residual restart constant",     "SNES",ngmres->gammaC,&ngmres->gammaC,NULL);CHKERRQ(ierr);
  ierr = PetscOptionsReal("-snes_ngmres_epsilonB",  "Difference selection constant", "SNES",ngmres->epsilonB,&ngmres->epsilonB,NULL);CHKERRQ(ierr);
  ierr = PetscOptionsReal("-snes_ngmres_deltaB",    "Difference residual selection constant", "SNES",ngmres->deltaB,&ngmres->deltaB,NULL);CHKERRQ(ierr);
  ierr = PetscOptionsBool("-snes_ngmres_single_reduction", "Aggregate reductions",  "SNES",ngmres->singlereduction,&ngmres->singlereduction,NULL);CHKERRQ(ierr);
  ierr = PetscOptionsTail();CHKERRQ(ierr);
  if ((ngmres->gammaA > ngmres->gammaC) && (ngmres->gammaC > 2.)) ngmres->gammaC = ngmres->gammaA;

  /* set the default type of the line search if the user hasn't already. */
  if (!snes->linesearch) {
    ierr = SNESGetSNESLineSearch(snes,&linesearch);CHKERRQ(ierr);
    ierr = SNESLineSearchSetType(linesearch,SNESLINESEARCHBASIC);CHKERRQ(ierr);
  }
  PetscFunctionReturn(0);
}

#undef __FUNCT__
#define __FUNCT__ "SNESView_NGMRES"
PetscErrorCode SNESView_NGMRES(SNES snes,PetscViewer viewer)
{
  SNES_NGMRES    *ngmres = (SNES_NGMRES*) snes->data;
  PetscBool      iascii;
  PetscErrorCode ierr;

  PetscFunctionBegin;
  ierr = PetscObjectTypeCompare((PetscObject) viewer,PETSCVIEWERASCII,&iascii);CHKERRQ(ierr);
  if (iascii) {
    ierr = PetscViewerASCIIPrintf(viewer,"  Number of stored past updates: %d\n", ngmres->msize);CHKERRQ(ierr);
    ierr = PetscViewerASCIIPrintf(viewer,"  Residual selection: gammaA=%1.0e, gammaC=%1.0e\n",ngmres->gammaA,ngmres->gammaC);CHKERRQ(ierr);
    ierr = PetscViewerASCIIPrintf(viewer,"  Difference restart: epsilonB=%1.0e, deltaB=%1.0e\n",ngmres->epsilonB,ngmres->deltaB);CHKERRQ(ierr);
  }
  PetscFunctionReturn(0);
}

#undef __FUNCT__
#define __FUNCT__ "SNESSolve_NGMRES"
PetscErrorCode SNESSolve_NGMRES(SNES snes)
{

  SNES_NGMRES *ngmres = (SNES_NGMRES*) snes->data;
  /* present solution, residual, and preconditioned residual */
  Vec X,F,B,D,Y;

  /* candidate linear combination answers */
  Vec XA,FA,XM,FM,FPC;

  /* coefficients and RHS to the minimization problem */
  PetscReal fnorm,fMnorm,fAnorm;
  PetscInt  k,k_restart,l,ivec,restart_count = 0;

  /* solution selection data */
  PetscBool selectRestart;
  PetscReal dnorm,dminnorm = 0.0;
  PetscReal fminnorm,xnorm,ynorm;

  SNESConvergedReason reason;
  PetscBool           lssucceed;
  PetscErrorCode      ierr;

  PetscFunctionBegin;
  /* variable initialization */
  snes->reason = SNES_CONVERGED_ITERATING;
  X            = snes->vec_sol;
  F            = snes->vec_func;
  B            = snes->vec_rhs;
  XA           = snes->vec_sol_update;
  FA           = snes->work[0];
  D            = snes->work[1];

  /* work for the line search */
  Y  = snes->work[2];
  XM = snes->work[3];
  FM = snes->work[4];

  ierr       = PetscObjectTakeAccess(snes);CHKERRQ(ierr);
  snes->iter = 0;
  snes->norm = 0.;
  ierr       = PetscObjectGrantAccess(snes);CHKERRQ(ierr);

  /* initialization */

  /* r = F(x) */
  if (!snes->vec_func_init_set) {
    ierr = SNESComputeFunction(snes,X,F);CHKERRQ(ierr);
    if (snes->domainerror) {
      snes->reason = SNES_DIVERGED_FUNCTION_DOMAIN;
      PetscFunctionReturn(0);
    }
  } else snes->vec_func_init_set = PETSC_FALSE;

  if (!snes->norm_init_set) {
    ierr = VecNorm(F,NORM_2,&fnorm);CHKERRQ(ierr);
    if (PetscIsInfOrNanReal(fnorm)) {
      snes->reason = SNES_DIVERGED_FNORM_NAN;
      PetscFunctionReturn(0);
    }
  } else {
    fnorm               = snes->norm_init;
    snes->norm_init_set = PETSC_FALSE;
  }
  fminnorm = fnorm;

  /* q_{00} = nu  */
  SNESNGMRESUpdateSubspace_Private(snes,0,0,F,fnorm,X);

  ierr       = PetscObjectTakeAccess(snes);CHKERRQ(ierr);
  snes->norm = fnorm;
  ierr       = PetscObjectGrantAccess(snes);CHKERRQ(ierr);
  ierr       = SNESLogConvergenceHistory(snes,fnorm,0);CHKERRQ(ierr);
  ierr       = SNESMonitor(snes,0,fnorm);CHKERRQ(ierr);
  ierr       = (*snes->ops->converged)(snes,0,0.0,0.0,fnorm,&snes->reason,snes->cnvP);CHKERRQ(ierr);
  if (snes->reason) PetscFunctionReturn(0);

  k_restart = 1;
  l         = 1;
  for (k=1; k < snes->max_its+1; k++) {
    /* select which vector of the stored subspace will be updated */
    ivec = k_restart % ngmres->msize; /* replace the last used part of the subspace */

    /* Computation of x^M */
    if (snes->pc && snes->pcside == PC_RIGHT) {
      ierr = VecCopy(X,XM);CHKERRQ(ierr);
      ierr = SNESSetInitialFunction(snes->pc,F);CHKERRQ(ierr);
      ierr = SNESSetInitialFunctionNorm(snes->pc,fnorm);CHKERRQ(ierr);

      ierr = PetscLogEventBegin(SNES_NPCSolve,snes->pc,XM,B,0);CHKERRQ(ierr);
      ierr = SNESSolve(snes->pc,B,XM);CHKERRQ(ierr);
      ierr = PetscLogEventEnd(SNES_NPCSolve,snes->pc,XM,B,0);CHKERRQ(ierr);

      ierr = SNESGetConvergedReason(snes->pc,&reason);CHKERRQ(ierr);
      if (reason < 0 && reason != SNES_DIVERGED_MAX_IT) {
        snes->reason = SNES_DIVERGED_INNER;
        PetscFunctionReturn(0);
      }
      ierr = SNESGetFunction(snes->pc,&FPC,NULL,NULL);CHKERRQ(ierr);
      ierr = VecCopy(FPC,FM);CHKERRQ(ierr);
      ierr = SNESGetFunctionNorm(snes->pc,&fMnorm);CHKERRQ(ierr);
    } else {
      /* no preconditioner -- just take gradient descent with line search */
      ierr = VecCopy(F,Y);CHKERRQ(ierr);
      ierr = VecCopy(F,FM);CHKERRQ(ierr);
      ierr = VecCopy(X,XM);CHKERRQ(ierr);

      fMnorm = fnorm;

      ierr = SNESLineSearchApply(snes->linesearch,XM,FM,&fMnorm,Y);CHKERRQ(ierr);
      ierr = SNESLineSearchGetSuccess(snes->linesearch,&lssucceed);CHKERRQ(ierr);
      if (!lssucceed) {
        if (++snes->numFailures >= snes->maxFailures) {
          snes->reason = SNES_DIVERGED_LINE_SEARCH;
          PetscFunctionReturn(0);
        }
      }
    }
    ierr = SNESNGMRESFormCombinedSolution_Private(snes,l,XM,FM,fMnorm,X,XA,FA);CHKERRQ(ierr);
    /* r = F(x) */
    if (fminnorm > fMnorm) fminnorm = fMnorm;  /* the minimum norm is now of F^M */

    /* differences for selection and restart */
    if (ngmres->restart_type == SNES_NGMRES_RESTART_DIFFERENCE || ngmres->select_type == SNES_NGMRES_SELECT_DIFFERENCE) {
      ierr = SNESNGMRESCalculateDifferences_Private(snes,l,X,F,XM,FM,XA,FA,D,&dnorm,&dminnorm,&fAnorm);CHKERRQ(ierr);
    } else {
      ierr = VecNorm(FA,NORM_2,&fAnorm);CHKERRQ(ierr);
    }
    if (PetscIsInfOrNanReal(fAnorm)) {
      snes->reason = SNES_DIVERGED_FNORM_NAN;
      PetscFunctionReturn(0);
    }

    /* combination (additive) or selection (multiplicative) of the N-GMRES solution */
    ierr          = SNESNGMRESSelect_Private(snes,k_restart,XM,FM,fMnorm,XA,FA,fAnorm,dnorm,fminnorm,dminnorm,X,F,Y,&fnorm);CHKERRQ(ierr);
    selectRestart = PETSC_FALSE;
    if (ngmres->restart_type == SNES_NGMRES_RESTART_DIFFERENCE) {
      ierr = SNESNGMRESSelectRestart_Private(snes,l,fAnorm,dnorm,fminnorm,dminnorm,&selectRestart);CHKERRQ(ierr);
      /* if the restart conditions persist for more than restart_it iterations, restart. */
      if (selectRestart) restart_count++;
      else restart_count = 0;
    } else if (ngmres->restart_type == SNES_NGMRES_RESTART_PERIODIC) {
      if (k_restart > ngmres->restart_periodic) {
        if (ngmres->monitor) ierr = PetscViewerASCIIPrintf(ngmres->monitor,"periodic restart after %D iterations\n",k_restart);CHKERRQ(ierr);
        restart_count = ngmres->restart_it;
      }
    }
    /* restart after restart conditions have persisted for a fixed number of iterations */
    if (restart_count >= ngmres->restart_it) {
      if (ngmres->monitor) {
        ierr = PetscViewerASCIIPrintf(ngmres->monitor,"Restarted at iteration %d\n",k_restart);CHKERRQ(ierr);
      }
      restart_count = 0;
      k_restart     = 1;
      l             = 1;
      /* q_{00} = nu */
      if (ngmres->candidate) {
        ierr = SNESNGMRESUpdateSubspace_Private(snes,0,0,FM,fMnorm,XM);CHKERRQ(ierr);
      } else {
        ierr = SNESNGMRESUpdateSubspace_Private(snes,0,0,F,fMnorm,X);CHKERRQ(ierr);
      }
    } else {
      /* select the current size of the subspace */
      if (l < ngmres->msize) l++;
      k_restart++;
      /* place the current entry in the list of previous entries */
      if (ngmres->candidate) {
        if (fminnorm > fMnorm) fminnorm = fMnorm;
        ierr = SNESNGMRESUpdateSubspace_Private(snes,ivec,l,FM,fMnorm,XM);CHKERRQ(ierr);
      } else {
        if (fminnorm > fnorm) fminnorm = fnorm;
        ierr = SNESNGMRESUpdateSubspace_Private(snes,ivec,l,F,fnorm,X);CHKERRQ(ierr);
      }
    }

    ierr       = PetscObjectTakeAccess(snes);CHKERRQ(ierr);
    snes->iter = k;
    snes->norm = fnorm;
    ierr = PetscObjectGrantAccess(snes);CHKERRQ(ierr);
    ierr = SNESLogConvergenceHistory(snes,snes->norm,snes->iter);CHKERRQ(ierr);
    ierr = SNESMonitor(snes,snes->iter,snes->norm);CHKERRQ(ierr);
    ierr = VecNormBegin(Y,NORM_2,&ynorm);CHKERRQ(ierr);
    ierr = VecNormBegin(X,NORM_2,&xnorm);CHKERRQ(ierr);
    ierr = VecNormEnd(Y,NORM_2,&ynorm);CHKERRQ(ierr);
    ierr = VecNormEnd(X,NORM_2,&xnorm);CHKERRQ(ierr);
    ierr = (*snes->ops->converged)(snes,snes->iter,xnorm,ynorm,fnorm,&snes->reason,snes->cnvP);CHKERRQ(ierr);
    if (snes->reason) PetscFunctionReturn(0);
  }
  snes->reason = SNES_DIVERGED_MAX_IT;
  PetscFunctionReturn(0);
}

#undef __FUNCT__
#define __FUNCT__ "SNESNGMRESSetRestartType"
/*@
    SNESNGMRESSetRestartType - Sets the restart type for SNESNGMRES.

    Logically Collective on SNES

    Input Parameters:
+   snes - the iterative context
-   rtype - restart type

    Options Database:
+   -snes_ngmres_restart_type<difference,periodic,none> - set the restart type
-   -snes_ngmres_restart[30] - sets the number of iterations before restart for periodic

    Level: intermediate

    SNESNGMRESRestartTypes:
+   SNES_NGMRES_RESTART_NONE - never restart
.   SNES_NGMRES_RESTART_DIFFERENCE - restart based upon difference criteria
-   SNES_NGMRES_RESTART_PERIODIC - restart after a fixed number of iterations

    Notes:
    The default line search used is the L2 line search and it requires two additional function evaluations.

.keywords: SNES, SNESNGMRES, restart, type, set SNESLineSearch
@*/
PetscErrorCode SNESNGMRESSetRestartType(SNES snes,SNESNGMRESRestartType rtype)
{
  PetscErrorCode ierr;

  PetscFunctionBegin;
  PetscValidHeaderSpecific(snes,SNES_CLASSID,1);
  ierr = PetscTryMethod(snes,"SNESNGMRESSetRestartType_C",(SNES,SNESNGMRESRestartType),(snes,rtype));CHKERRQ(ierr);
  PetscFunctionReturn(0);
}

#undef __FUNCT__
#define __FUNCT__ "SNESNGMRESSetSelectType"
/*@
    SNESNGMRESSetSelectType - Sets the selection type for SNESNGMRES.  This determines how the candidate solution and
    combined solution are used to create the next iterate.

    Logically Collective on SNES

    Input Parameters:
+   snes - the iterative context
-   stype - selection type

    Options Database:
.   -snes_ngmres_select_type<difference,none,linesearch>

    Level: intermediate

    SNESNGMRESSelectTypes:
+   SNES_NGMRES_SELECT_NONE - choose the combined solution all the time
.   SNES_NGMRES_SELECT_DIFFERENCE - choose based upon the selection criteria
-   SNES_NGMRES_SELECT_LINESEARCH - choose based upon line search combination

    Notes:
    The default line search used is the L2 line search and it requires two additional function evaluations.

.keywords: SNES, SNESNGMRES, selection, type, set SNESLineSearch
@*/
PetscErrorCode SNESNGMRESSetSelectType(SNES snes,SNESNGMRESSelectType stype)
{
  PetscErrorCode ierr;

  PetscFunctionBegin;
  PetscValidHeaderSpecific(snes,SNES_CLASSID,1);
  ierr = PetscTryMethod(snes,"SNESNGMRESSetSelectType_C",(SNES,SNESNGMRESSelectType),(snes,stype));CHKERRQ(ierr);
  PetscFunctionReturn(0);
}

#undef __FUNCT__
#define __FUNCT__ "SNESNGMRESSetSelectType_NGMRES"
PetscErrorCode SNESNGMRESSetSelectType_NGMRES(SNES snes,SNESNGMRESSelectType stype)
{
  SNES_NGMRES *ngmres = (SNES_NGMRES*)snes->data;

  PetscFunctionBegin;
  ngmres->select_type = stype;
  PetscFunctionReturn(0);
}

#undef __FUNCT__
#define __FUNCT__ "SNESNGMRESSetRestartType_NGMRES"
PetscErrorCode SNESNGMRESSetRestartType_NGMRES(SNES snes,SNESNGMRESRestartType rtype)
{
  SNES_NGMRES *ngmres = (SNES_NGMRES*)snes->data;

  PetscFunctionBegin;
  ngmres->restart_type = rtype;
  PetscFunctionReturn(0);
}

/*MC
  SNESNGMRES - The Nonlinear Generalized Minimum Residual method.

   Level: beginner

   Options Database:
+  -snes_ngmres_select_type<difference,none,linesearch> - choose the select between candidate and combined solution
.  -snes_ngmres_restart_type<difference,none,periodic> - choose the restart conditions
.  -snes_ngmres_candidate        - Use NGMRES variant which combines candidate solutions instead of actual solutions
.  -snes_ngmres_m                - Number of stored previous solutions and residuals
.  -snes_ngmres_restart_it       - Number of iterations the restart conditions hold before restart
.  -snes_ngmres_gammaA           - Residual tolerance for solution select between the candidate and combination
.  -snes_ngmres_gammaC           - Residual tolerance for restart
.  -snes_ngmres_epsilonB         - Difference tolerance between subsequent solutions triggering restart
.  -snes_ngmres_deltaB           - Difference tolerance between residuals triggering restart
.  -snes_ngmres_monitor          - Prints relevant information about the ngmres iteration
.  -snes_linesearch_type <basic,basicnonorms,quadratic,critical> - Line search type used for the default smoother
-  -additive_snes_linesearch_type - linesearch type used to select between the candidate and combined solution with additive select type

   Notes:

   The N-GMRES method combines m previous solutions into a minimum-residual solution by solving a small linearized
   optimization problem at each iteration.

   References:

   "Krylov Subspace Acceleration of Nonlinear Multigrid with Application to Recirculating Flows", C. W. Oosterlee and T. Washio,
   SIAM Journal on Scientific Computing, 21(5), 2000.

.seealso: SNESCreate(), SNES, SNESSetType(), SNESType (for list of available types)
M*/

#undef __FUNCT__
#define __FUNCT__ "SNESCreate_NGMRES"
PETSC_EXTERN PetscErrorCode SNESCreate_NGMRES(SNES snes)
{
  SNES_NGMRES    *ngmres;
  PetscErrorCode ierr;

  PetscFunctionBegin;
  snes->ops->destroy        = SNESDestroy_NGMRES;
  snes->ops->setup          = SNESSetUp_NGMRES;
  snes->ops->setfromoptions = SNESSetFromOptions_NGMRES;
  snes->ops->view           = SNESView_NGMRES;
  snes->ops->solve          = SNESSolve_NGMRES;
  snes->ops->reset          = SNESReset_NGMRES;

  snes->usespc  = PETSC_TRUE;
  snes->usesksp = PETSC_FALSE;

  ierr          = PetscNewLog(snes,SNES_NGMRES,&ngmres);CHKERRQ(ierr);
  snes->data    = (void*) ngmres;
  ngmres->msize = 30;

  if (!snes->tolerancesset) {
    snes->max_funcs = 30000;
    snes->max_its   = 10000;
  }

  ngmres->candidate = PETSC_FALSE;

  ngmres->additive_linesearch = NULL;
  ngmres->approxfunc       = PETSC_FALSE;
  ngmres->restart_it       = 2;
  ngmres->restart_periodic = 30;
  ngmres->gammaA           = 2.0;
  ngmres->gammaC           = 2.0;
  ngmres->deltaB           = 0.9;
  ngmres->epsilonB         = 0.1;

  ngmres->restart_type = SNES_NGMRES_RESTART_DIFFERENCE;
  ngmres->select_type  = SNES_NGMRES_SELECT_DIFFERENCE;

  ierr = PetscObjectComposeFunction((PetscObject)snes,"SNESNGMRESSetSelectType_C","SNESNGMRESSetSelectType_NGMRES",SNESNGMRESSetSelectType_NGMRES);CHKERRQ(ierr);
  ierr = PetscObjectComposeFunction((PetscObject)snes,"SNESNGMRESSetRestartType_C","SNESNGMRESSetRestartType_NGMRES",SNESNGMRESSetRestartType_NGMRES);CHKERRQ(ierr);
  PetscFunctionReturn(0);
}