2:  #include <petsc/private/snesimpl.h>

  4: static PetscErrorCode SNESSolve_KSPONLY(SNES snes)
  5: {
  6:   PetscErrorCode     ierr;
  7:   PetscInt           lits;
  8:   Vec                Y,X,F;

 11:   if (snes->xl || snes->xu || snes->ops->computevariablebounds) SETERRQ1(PetscObjectComm((PetscObject)snes),PETSC_ERR_ARG_WRONGSTATE, "SNES solver %s does not support bounds", ((PetscObject)snes)->type_name);

 13:   snes->numFailures            = 0;
 14:   snes->numLinearSolveFailures = 0;
 15:   snes->reason                 = SNES_CONVERGED_ITERATING;
 16:   snes->iter                   = 0;
 17:   snes->norm                   = 0.0;

 19:   X = snes->vec_sol;
 20:   F = snes->vec_func;
 21:   Y = snes->vec_sol_update;

 23:   SNESComputeFunction(snes,X,F);
 24:   if (snes->numbermonitors) {
 25:     PetscReal fnorm;
 26:     VecNorm(F,NORM_2,&fnorm);
 27:     SNESMonitor(snes,0,fnorm);
 28:   }

 30:   /* Call general purpose update function */
 31:   if (snes->ops->update) {
 32:     (*snes->ops->update)(snes, 0);
 33:   }

 35:   /* Solve J Y = F, where J is Jacobian matrix */
 36:   SNESComputeJacobian(snes,X,snes->jacobian,snes->jacobian_pre);
 37:   KSPSetOperators(snes->ksp,snes->jacobian,snes->jacobian_pre);
 38:   KSPSolve(snes->ksp,F,Y);
 39:   snes->reason = SNES_CONVERGED_ITS;
 40:   SNESCheckKSPSolve(snes);

 42:   KSPGetIterationNumber(snes->ksp,&lits);
 43:   snes->linear_its += lits;
 44:   PetscInfo2(snes,"iter=%D, linear solve iterations=%D\n",snes->iter,lits);
 45:   snes->iter++;

 47:   /* Take the computed step. */
 48:   VecAXPY(X,-1.0,Y);
 49:   if (snes->numbermonitors) {
 50:     PetscReal fnorm;
 51:     SNESComputeFunction(snes,X,F);
 52:     VecNorm(F,NORM_2,&fnorm);
 53:     SNESMonitor(snes,1,fnorm);
 54:   }
 55:   return(0);
 56: }

 58: static PetscErrorCode SNESSetUp_KSPONLY(SNES snes)
 59: {

 63:   SNESSetUpMatrices(snes);
 64:   return(0);
 65: }

 67: static PetscErrorCode SNESDestroy_KSPONLY(SNES snes)
 68: {

 71:   return(0);
 72: }

 74: /* -------------------------------------------------------------------------- */
 75: /*MC
 76:       SNESKSPONLY - Nonlinear solver that only performs one Newton step and does not compute any norms.
 77:       The main purpose of this solver is to solve linear problems using the SNES interface, without
 78:       any additional overhead in the form of vector operations.

 80:    Level: beginner

 82: .seealso:  SNESCreate(), SNES, SNESSetType(), SNESNEWTONLS, SNESNEWTONTR
 83: M*/
 84: PETSC_EXTERN PetscErrorCode SNESCreate_KSPONLY(SNES snes)
 85: {

 88:   snes->ops->setup          = SNESSetUp_KSPONLY;
 89:   snes->ops->solve          = SNESSolve_KSPONLY;
 90:   snes->ops->destroy        = SNESDestroy_KSPONLY;
 91:   snes->ops->setfromoptions = 0;
 92:   snes->ops->view           = 0;
 93:   snes->ops->reset          = 0;

 95:   snes->usesksp = PETSC_TRUE;
 96:   snes->usesnpc = PETSC_FALSE;

 98:   snes->alwayscomputesfinalresidual = PETSC_FALSE;

100:   snes->data = 0;
101:   return(0);
102: }