Date: 2025-03-28T21:10:52+00:00

Actual source code: modpcf.c

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

      3: /*@C
      4:   KSPFGMRESSetModifyPC - Sets the routine used by `KSPFGMRES` to modify the preconditioner. [](sec_flexibleksp)

      6:   Logically Collective

      8:   Input Parameters:
      9: + ksp     - iterative context obtained from `KSPCreate()`
     10: . fcn     - modifypc function
     11: . ctx     - optional context
     12: - destroy - optional context destroy routine

     14:   Calling sequence of `fcn`:
     15: + ksp       - the ksp context being used.
     16: . total_its - the total number of FGMRES iterations that have occurred.
     17: . local_its - the number of FGMRES iterations since last restart.
     18: . res_norm  - the current residual norm.
     19: - ctx       - optional context variable

     21:   Calling sequence of `destroy`:
     22: . ctx - the function context

     24:   Options Database Keys:
     25: + -ksp_fgmres_modifypcnochange - do not change the `PC`
     26: - -ksp_fgmres_modifypcksp      - changes the inner KSP solver tolerances

     28:   Level: intermediate

     30:   Note:
     31:   Several `fcn` routines are predefined, including `KSPFGMRESModifyPCNoChange()`, and  `KSPFGMRESModifyPCKSP()`

     33: .seealso: [](ch_ksp), [](sec_flexibleksp), `KSPFGMRES`, `KSPFGMRESModifyPCNoChange()`, `KSPFGMRESModifyPCKSP()`
     34: @*/
     35: PetscErrorCode KSPFGMRESSetModifyPC(KSP ksp, PetscErrorCode (*fcn)(KSP ksp, PetscInt total_its, PetscInt local_its, PetscReal res_norm, void *ctx), void *ctx, PetscErrorCode (*destroy)(void *ctx))
     36: {
     37:   PetscFunctionBegin;
     39:   PetscTryMethod(ksp, "KSPFGMRESSetModifyPC_C", (KSP, PetscErrorCode (*)(KSP, PetscInt, PetscInt, PetscReal, void *), void *, PetscErrorCode (*)(void *)), (ksp, fcn, ctx, destroy));
     40:   PetscFunctionReturn(PETSC_SUCCESS);
     41: }

     43: /*@
     44:   KSPFGMRESModifyPCNoChange - this is the default used by `KSPFMGMRES` - it doesn't change the preconditioner. [](sec_flexibleksp)

     46:   Input Parameters:
     47: + ksp       - the ksp context being used.
     48: . total_its - the total number of `KSPFGMRES` iterations that have occurred.
     49: . loc_its   - the number of `KSPFGMRES` iterations since last restart.
     50: . res_norm  - the current residual norm.
     51: - ctx       - context variable, unused in this routine

     53:   Level: intermediate

     55: .seealso: [](ch_ksp), [](sec_flexibleksp), `KSPFGMRES`, `KSPFGMRESSetModifyPC()`, `KSPFGMRESModifyPCKSP()`
     56: @*/
     57: PetscErrorCode KSPFGMRESModifyPCNoChange(KSP ksp, PetscInt total_its, PetscInt loc_its, PetscReal res_norm, void *ctx)
     58: {
     59:   PetscFunctionBegin;
     60:   PetscFunctionReturn(PETSC_SUCCESS);
     61: }

     63: /*@
     64:   KSPFGMRESModifyPCKSP - modifies the attributes of the `KSPFGMRES` preconditioner, see [](sec_flexibleksp).

     66:   Input Parameters:
     67: + ksp       - the ksp context being used.
     68: . total_its - the total number of `KSPFGMRES` iterations that have occurred.
     69: . loc_its   - the number of `KSPFGMRES` iterations since last restart.
     70: . res_norm  - the current residual norm.
     71: - ctx       - context, not used here

     73:   Level: intermediate

     75:   Note:
     76:   You can use this as a template for writing a custom modification callback

     78: .seealso: [](ch_ksp), [](sec_flexibleksp), `KSPFGMRES`, `KSPFGMRESSetModifyPC()`
     79: @*/
     80: PetscErrorCode KSPFGMRESModifyPCKSP(KSP ksp, PetscInt total_its, PetscInt loc_its, PetscReal res_norm, void *ctx)
     81: {
     82:   PC        pc;
     83:   PetscInt  maxits;
     84:   KSP       sub_ksp;
     85:   PetscReal rtol, abstol, dtol;
     86:   PetscBool isksp;

     88:   PetscFunctionBegin;
     89:   PetscCall(KSPGetPC(ksp, &pc));

     91:   PetscCall(PetscObjectTypeCompare((PetscObject)pc, PCKSP, &isksp));
     92:   if (isksp) {
     93:     PetscCall(PCKSPGetKSP(pc, &sub_ksp));

     95:     /* note that at this point you could check the type of KSP with KSPGetType() */

     97:     /* Now we can use functions such as KSPGMRESSetRestart() or
     98:       KSPGMRESSetOrthogonalization() or KSPSetTolerances() */

    100:     PetscCall(KSPGetTolerances(sub_ksp, &rtol, &abstol, &dtol, &maxits));
    101:     if (!loc_its) rtol = .1;
    102:     else rtol *= .9;
    103:     PetscCall(KSPSetTolerances(sub_ksp, rtol, abstol, dtol, maxits));
    104:   }
    105:   PetscFunctionReturn(PETSC_SUCCESS);
    106: }