Date: 2025-03-28T21:11:07+00:00

Actual source code: snespc.c

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

      3: /*@
      4:   SNESApplyNPC - Calls `SNESSolve()` on the preconditioner for the `SNES`

      6:   Collective

      8:   Input Parameters:
      9: + snes - the `SNES` context
     10: . x    - input vector
     11: - f    - optional; the function evaluation on `x`

     13:   Output Parameter:
     14: . y - function vector, as set by `SNESSetFunction()`

     16:   Level: developer

     18:   Note:
     19:   `SNESComputeFunction()` should be called on `x` before `SNESApplyNPC()` is called, as it is
     20:   with `SNESComuteJacobian()`.

     22: .seealso: [](ch_snes), `SNES`, `SNESGetNPC()`, `SNESSetNPC()`, `SNESComputeFunction()`
     23: @*/
     24: PetscErrorCode SNESApplyNPC(SNES snes, Vec x, Vec f, Vec y)
     25: {
     26:   PetscFunctionBegin;
     30:   PetscCheckSameComm(snes, 1, x, 2);
     31:   PetscCheckSameComm(snes, 1, y, 4);
     32:   PetscCall(VecValidValues_Internal(x, 2, PETSC_TRUE));
     33:   if (snes->npc) {
     34:     if (f) PetscCall(SNESSetInitialFunction(snes->npc, f));
     35:     PetscCall(VecCopy(x, y));
     36:     PetscCall(PetscLogEventBegin(SNES_NPCSolve, snes->npc, x, y, 0));
     37:     PetscCall(SNESSolve(snes->npc, snes->vec_rhs, y));
     38:     PetscCall(PetscLogEventEnd(SNES_NPCSolve, snes->npc, x, y, 0));
     39:     PetscCall(VecAYPX(y, -1.0, x));
     40:   }
     41:   PetscFunctionReturn(PETSC_SUCCESS);
     42: }

     44: PetscErrorCode SNESComputeFunctionDefaultNPC(SNES snes, Vec X, Vec F)
     45: {
     46:   /* This is to be used as an argument to SNESMF -- NOT as a "function" */
     47:   SNESConvergedReason reason;

     49:   PetscFunctionBegin;
     50:   if (snes->npc) {
     51:     PetscCall(SNESApplyNPC(snes, X, NULL, F));
     52:     PetscCall(SNESGetConvergedReason(snes->npc, &reason));
     53:     if (reason < 0 && reason != SNES_DIVERGED_MAX_IT) PetscCall(SNESSetFunctionDomainError(snes));
     54:   } else {
     55:     PetscCall(SNESComputeFunction(snes, X, F));
     56:   }
     57:   PetscFunctionReturn(PETSC_SUCCESS);
     58: }

     60: /*@
     61:   SNESGetNPCFunction - Gets the current function value and its norm from a nonlinear preconditioner after `SNESSolve()` has been called on that `SNES`

     63:   Collective

     65:   Input Parameter:
     66: . snes - the `SNES` context

     68:   Output Parameters:
     69: + F     - function vector
     70: - fnorm - the norm of `F`

     72:   Level: developer

     74: .seealso: [](ch_snes), `SNES`, `SNESGetNPC()`, `SNESSetNPC()`, `SNESComputeFunction()`, `SNESApplyNPC()`, `SNESSolve()`
     75: @*/
     76: PetscErrorCode SNESGetNPCFunction(SNES snes, Vec F, PetscReal *fnorm)
     77: {
     78:   PCSide           npcside;
     79:   SNESFunctionType functype;
     80:   SNESNormSchedule normschedule;
     81:   Vec              FPC, XPC;

     83:   PetscFunctionBegin;
     85:   if (fnorm) PetscAssertPointer(fnorm, 3);
     86:   PetscCheck(snes->npc, PETSC_COMM_SELF, PETSC_ERR_ARG_WRONGSTATE, "No nonlinear preconditioner set");
     87:   PetscCall(SNESGetNPCSide(snes->npc, &npcside));
     88:   PetscCall(SNESGetFunctionType(snes->npc, &functype));
     89:   PetscCall(SNESGetNormSchedule(snes->npc, &normschedule));

     91:   /* check if the function is valid based upon how the inner solver is preconditioned */
     92:   if (normschedule != SNES_NORM_NONE && normschedule != SNES_NORM_INITIAL_ONLY && (npcside == PC_RIGHT || functype == SNES_FUNCTION_UNPRECONDITIONED)) {
     93:     PetscCall(SNESGetFunction(snes->npc, &FPC, NULL, NULL));
     94:     PetscCheck(FPC, PETSC_COMM_SELF, PETSC_ERR_ARG_WRONGSTATE, "Nonlinear preconditioner has no function");
     95:     if (fnorm) PetscCall(VecNorm(FPC, NORM_2, fnorm));
     96:     PetscCall(VecCopy(FPC, F));
     97:   } else {
     98:     PetscCall(SNESGetSolution(snes->npc, &XPC));
     99:     PetscCheck(XPC, PETSC_COMM_SELF, PETSC_ERR_ARG_WRONGSTATE, "Nonlinear preconditioner has no solution");
    100:     PetscCall(SNESComputeFunction(snes->npc, XPC, F));
    101:     if (fnorm) PetscCall(VecNorm(F, NORM_2, fnorm));
    102:   }
    103:   PetscFunctionReturn(PETSC_SUCCESS);
    104: }