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

  3: typedef struct {
  4:   PetscBool transpose_solve;
  5: } SNES_KSPONLY;

  7: static PetscErrorCode SNESSolve_KSPONLY(SNES snes)
  8: {
  9:   SNES_KSPONLY *ksponly = (SNES_KSPONLY *)snes->data;
 10:   PetscInt      lits;
 11:   Vec           Y, X, F;

 13:   PetscFunctionBegin;
 14:   PetscCheck(!snes->xl && !snes->xu && !snes->ops->computevariablebounds, PetscObjectComm((PetscObject)snes), PETSC_ERR_ARG_WRONGSTATE, "SNES solver %s does not support bounds", ((PetscObject)snes)->type_name);

 16:   snes->numFailures            = 0;
 17:   snes->numLinearSolveFailures = 0;
 18:   snes->reason                 = SNES_CONVERGED_ITERATING;
 19:   snes->iter                   = 0;
 20:   snes->norm                   = 0.0;

 22:   X = snes->vec_sol;
 23:   F = snes->vec_func;
 24:   Y = snes->vec_sol_update;

 26:   if (!snes->vec_func_init_set) {
 27:     PetscCall(SNESComputeFunction(snes, X, F));
 28:   } else snes->vec_func_init_set = PETSC_FALSE;

 30:   if (snes->numbermonitors) {
 31:     PetscReal fnorm;
 32:     PetscCall(VecNorm(F, NORM_2, &fnorm));
 33:     SNESCheckFunctionNorm(snes, fnorm);
 34:     PetscCall(SNESMonitor(snes, 0, fnorm));
 35:   }

 37:   /* Call general purpose update function */
 38:   PetscTryTypeMethod(snes, update, 0);

 40:   /* Solve J Y = F, where J is Jacobian matrix */
 41:   PetscCall(SNESComputeJacobian(snes, X, snes->jacobian, snes->jacobian_pre));

 43:   SNESCheckJacobianDomainerror(snes);

 45:   PetscCall(KSPSetOperators(snes->ksp, snes->jacobian, snes->jacobian_pre));
 46:   if (ksponly->transpose_solve) {
 47:     PetscCall(KSPSolveTranspose(snes->ksp, F, Y));
 48:   } else {
 49:     PetscCall(KSPSolve(snes->ksp, F, Y));
 50:   }
 51:   snes->reason = SNES_CONVERGED_ITS;
 52:   SNESCheckKSPSolve(snes);

 54:   PetscCall(KSPGetIterationNumber(snes->ksp, &lits));
 55:   PetscCall(PetscInfo(snes, "iter=%" PetscInt_FMT ", linear solve iterations=%" PetscInt_FMT "\n", snes->iter, lits));
 56:   snes->iter++;

 58:   /* Take the computed step. */
 59:   PetscCall(VecAXPY(X, -1.0, Y));
 60:   if (snes->numbermonitors) {
 61:     PetscReal fnorm;
 62:     PetscCall(SNESComputeFunction(snes, X, F));
 63:     PetscCall(VecNorm(F, NORM_2, &fnorm));
 64:     SNESCheckFunctionNorm(snes, fnorm);
 65:     PetscCall(SNESMonitor(snes, 1, fnorm));
 66:   }
 67:   PetscFunctionReturn(PETSC_SUCCESS);
 68: }

 70: static PetscErrorCode SNESSetUp_KSPONLY(SNES snes)
 71: {
 72:   PetscFunctionBegin;
 73:   PetscCall(SNESSetUpMatrices(snes));
 74:   PetscFunctionReturn(PETSC_SUCCESS);
 75: }

 77: static PetscErrorCode SNESDestroy_KSPONLY(SNES snes)
 78: {
 79:   PetscFunctionBegin;
 80:   PetscCall(PetscFree(snes->data));
 81:   PetscFunctionReturn(PETSC_SUCCESS);
 82: }

 84: /*MC
 85:    SNESKSPONLY - Nonlinear solver that performs one Newton step with `KSPSolve()` and does not compute any norms.

 87:    Level: beginner

 89:    Note:
 90:    The main purpose of this solver is to solve linear problems using the `SNES` interface, without
 91:    any additional overhead in the form of vector norm operations.

 93: .seealso: [](ch_snes), `SNES`, `SNESType`, `SNESCreate()`, `SNES`, `SNESSetType()`, `SNESNEWTONLS`, `SNESNEWTONTR`, `SNESKSPTRANSPOSEONLY`
 94: M*/
 95: PETSC_EXTERN PetscErrorCode SNESCreate_KSPONLY(SNES snes)
 96: {
 97:   SNES_KSPONLY *ksponly;

 99:   PetscFunctionBegin;
100:   snes->ops->setup          = SNESSetUp_KSPONLY;
101:   snes->ops->solve          = SNESSolve_KSPONLY;
102:   snes->ops->destroy        = SNESDestroy_KSPONLY;
103:   snes->ops->setfromoptions = NULL;
104:   snes->ops->view           = NULL;
105:   snes->ops->reset          = NULL;

107:   snes->usesksp = PETSC_TRUE;
108:   snes->usesnpc = PETSC_FALSE;

110:   snes->alwayscomputesfinalresidual = PETSC_FALSE;

112:   PetscCall(SNESParametersInitialize(snes));

114:   PetscCall(PetscNew(&ksponly));
115:   snes->data = (void *)ksponly;
116:   PetscFunctionReturn(PETSC_SUCCESS);
117: }

119: /*MC
120:    SNESKSPTRANSPOSEONLY - Nonlinear solver that performs one Newton step with `KSPSolveTranspose()` and does not compute any norms.

122:    Level: beginner

124:    Note:
125:    The main purpose of this solver is to solve transposed linear problems using the `SNES` interface, without
126:    any additional overhead in the form of vector operations within adjoint solvers.

128: .seealso: [](ch_snes), `SNES`, `SNESType`, `SNESCreate()`, `SNES`, `SNESSetType()`, `SNESKS`, `SNESNEWTONLS`, `SNESNEWTONTR`
129: M*/
130: PETSC_EXTERN PetscErrorCode SNESCreate_KSPTRANSPOSEONLY(SNES snes)
131: {
132:   SNES_KSPONLY *kspo;

134:   PetscFunctionBegin;
135:   PetscCall(SNESCreate_KSPONLY(snes));
136:   PetscCall(PetscObjectChangeTypeName((PetscObject)snes, SNESKSPTRANSPOSEONLY));
137:   kspo                  = (SNES_KSPONLY *)snes->data;
138:   kspo->transpose_solve = PETSC_TRUE;
139:   PetscFunctionReturn(PETSC_SUCCESS);
140: }