Actual source code: preonly.c
1: #include <petsc/private/kspimpl.h>
3: static PetscErrorCode KSPSetUp_PREONLY(KSP ksp)
4: {
5: PetscFunctionBegin;
6: PetscFunctionReturn(PETSC_SUCCESS);
7: }
9: static PetscErrorCode KSPSolve_PREONLY(KSP ksp)
10: {
11: PetscReal norm;
12: PetscBool flg;
13: PCFailedReason pcreason;
15: PetscFunctionBegin;
16: PetscCall(PCGetDiagonalScale(ksp->pc, &flg));
17: PetscCheck(!flg, PetscObjectComm((PetscObject)ksp), PETSC_ERR_SUP, "Krylov method %s does not support diagonal scaling", ((PetscObject)ksp)->type_name);
18: if (!ksp->guess_zero) {
19: PetscCall(PetscObjectTypeCompareAny((PetscObject)ksp->pc, &flg, PCREDISTRIBUTE, PCMPI, ""));
20: PetscCheck(flg, PetscObjectComm((PetscObject)ksp), PETSC_ERR_USER, "KSP of type preonly (application of preconditioner only) doesn't make sense with nonzero initial guess you probably want a KSP of type Richardson");
21: }
22: ksp->its = 0;
23: if (ksp->numbermonitors) {
24: PetscCall(VecNorm(ksp->vec_rhs, NORM_2, &norm));
25: PetscCall(KSPMonitor(ksp, 0, norm));
26: }
27: PetscCall(KSP_PCApply(ksp, ksp->vec_rhs, ksp->vec_sol));
28: PetscCall(PCReduceFailedReason(ksp->pc));
29: PetscCall(PCGetFailedReason(ksp->pc, &pcreason));
30: PetscCall(VecFlag(ksp->vec_sol, pcreason));
31: if (pcreason) {
32: PetscCheck(!ksp->errorifnotconverged, PetscObjectComm((PetscObject)ksp), PETSC_ERR_NOT_CONVERGED, "KSPSolve has not converged with PCFailedReason %s", PCFailedReasons[pcreason]);
33: ksp->reason = KSP_DIVERGED_PC_FAILED;
34: } else {
35: ksp->its = 1;
36: ksp->reason = KSP_CONVERGED_ITS;
37: }
38: if (ksp->numbermonitors) {
39: Vec v;
40: Mat A;
42: PetscCall(VecDuplicate(ksp->vec_rhs, &v));
43: PetscCall(PCGetOperators(ksp->pc, &A, NULL));
44: PetscCall(KSP_MatMult(ksp, A, ksp->vec_sol, v));
45: PetscCall(VecAYPX(v, -1.0, ksp->vec_rhs));
46: PetscCall(VecNorm(v, NORM_2, &norm));
47: PetscCall(VecDestroy(&v));
48: PetscCall(KSPMonitor(ksp, 1, norm));
49: }
50: PetscFunctionReturn(PETSC_SUCCESS);
51: }
53: static PetscErrorCode KSPMatSolve_PREONLY(KSP ksp, Mat B, Mat X)
54: {
55: PetscBool diagonalscale;
56: PCFailedReason pcreason;
58: PetscFunctionBegin;
59: PetscCall(PCGetDiagonalScale(ksp->pc, &diagonalscale));
60: PetscCheck(!diagonalscale, PetscObjectComm((PetscObject)ksp), PETSC_ERR_SUP, "Krylov method %s does not support diagonal scaling", ((PetscObject)ksp)->type_name);
61: PetscCheck(ksp->guess_zero, PetscObjectComm((PetscObject)ksp), PETSC_ERR_USER, "Running KSP of preonly doesn't make sense with nonzero initial guess you probably want a KSP type of Richardson");
62: ksp->its = 0;
63: PetscCall(KSP_PCMatApply(ksp, B, X));
64: PetscCall(PCGetFailedReason(ksp->pc, &pcreason));
65: /* Note: only some ranks may have this set; this may lead to problems if the caller assumes ksp->reason is set on all processes or just uses the result */
66: if (pcreason) {
67: PetscCall(MatSetInf(X));
68: ksp->reason = KSP_DIVERGED_PC_FAILED;
69: } else {
70: ksp->its = 1;
71: ksp->reason = KSP_CONVERGED_ITS;
72: }
73: PetscFunctionReturn(PETSC_SUCCESS);
74: }
76: /*MC
77: KSPNONE - An alias for `KSPPREONLY`
79: Options Database Key:
80: . -ksp_type none - use a single application of the preconditioner only
82: Level: beginner
84: Note:
85: See `KSPPREONLY` for more details
87: .seealso: [](ch_ksp), `KSPCreate()`, `KSPSetType()`, `KSPType`, `KSPPREONLY`, `KSP`, `KSPRICHARDSON`, `KSPCHEBYSHEV`, `KSPGetPC()`, `KSPSetInitialGuessNonzero()`,
88: `PCREDISTRIBUTE`, `PCRedistributeGetKSP()`, `KSPPREONLY`
89: M*/
91: /*MC
92: KSPPREONLY - This implements a method that applies ONLY the preconditioner exactly once.
94: It is commonly used with the direct solver preconditioners like `PCLU` and `PCCHOLESKY`, but it may also be used when a single iteration of the
95: preconditioner is needed for smoothing in multigrid, `PCMG` or `PCGAMG` or within some other nested linear solve such as `PCFIELDSPLIT` or `PCBJACOBI`.
97: There is an alias of this with the name `KSPNONE`.
99: Options Database Key:
100: . -ksp_type preonly - use a single application of the preconditioner only
102: Level: beginner
104: Notes:
105: Since this does not involve an iteration the basic `KSP` parameters such as tolerances and maximum iteration counts
106: do not apply
108: To apply the preconditioner multiple times in a simple iteration use `KSPRICHARDSON`
110: This `KSPType` cannot be used with the flag `-ksp_initial_guess_nonzero` or the call `KSPSetInitialGuessNonzero()` since it simply applies
111: the preconditioner to the given right-hand side during `KSPSolve()`. Except when the
112: `PCType` is `PCREDISTRIBUTE`; in that situation pass the nonzero initial guess flag with `-ksp_initial_guess_nonzero` or `KSPSetInitialGuessNonzero()`
113: both to the outer `KSP` (which is `KSPPREONLY`) and the inner `KSP` object obtained with `KSPGetPC()` followed by `PCRedistributedGetKSP()`
114: followed by `KSPSetInitialGuessNonzero()` or the option `-redistribute_ksp_initial_guess_nonzero`.
116: Developer Note:
117: Even though this method does not use any norms, the user is allowed to set the `KSPNormType` to any value.
118: This is so the users does not have to change `KSPNormType` options when they switch from other `KSP` methods to this one.
120: .seealso: [](ch_ksp), `KSPCreate()`, `KSPSetType()`, `KSPType`, `KSP`, `KSPRICHARDSON`, `KSPCHEBYSHEV`, `KSPGetPC()`, `KSPSetInitialGuessNonzero()`,
121: `PCREDISTRIBUTE`, `PCRedistributeGetKSP()`, `KSPNONE`
122: M*/
124: PETSC_EXTERN PetscErrorCode KSPCreate_PREONLY(KSP ksp)
125: {
126: PetscFunctionBegin;
127: PetscCall(KSPSetSupportedNorm(ksp, KSP_NORM_NONE, PC_LEFT, 3));
128: PetscCall(KSPSetSupportedNorm(ksp, KSP_NORM_NONE, PC_RIGHT, 2));
129: PetscCall(KSPSetSupportedNorm(ksp, KSP_NORM_PRECONDITIONED, PC_LEFT, 2));
130: PetscCall(KSPSetSupportedNorm(ksp, KSP_NORM_PRECONDITIONED, PC_RIGHT, 2));
131: PetscCall(KSPSetSupportedNorm(ksp, KSP_NORM_UNPRECONDITIONED, PC_LEFT, 2));
132: PetscCall(KSPSetSupportedNorm(ksp, KSP_NORM_UNPRECONDITIONED, PC_RIGHT, 2));
133: PetscCall(KSPSetSupportedNorm(ksp, KSP_NORM_NATURAL, PC_LEFT, 2));
135: ksp->data = NULL;
136: ksp->ops->setup = KSPSetUp_PREONLY;
137: ksp->ops->solve = KSPSolve_PREONLY;
138: ksp->ops->matsolve = KSPMatSolve_PREONLY;
139: ksp->ops->destroy = KSPDestroyDefault;
140: ksp->ops->buildsolution = KSPBuildSolutionDefault;
141: ksp->ops->buildresidual = KSPBuildResidualDefault;
142: ksp->ops->setfromoptions = NULL;
143: ksp->ops->view = NULL;
144: ksp->guess_not_read = PETSC_TRUE; // A KSP of preonly never needs to zero the input x since PC do not use an initial guess
145: PetscFunctionReturn(PETSC_SUCCESS);
146: }