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 (for the callback function provided by `SNESSetFunction()`,
 62:   and its norm from a nonlinear preconditioner after `SNESSolve()` has been called on that `SNES`

 64:   Collective

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

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

 73:   Level: developer

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

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

 92:   /* check if the function is valid based upon how the inner solver is preconditioned */
 93:   if (normschedule != SNES_NORM_NONE && normschedule != SNES_NORM_INITIAL_ONLY && (npcside == PC_RIGHT || functype == SNES_FUNCTION_UNPRECONDITIONED)) {
 94:     PetscCall(SNESGetFunction(snes->npc, &FPC, NULL, NULL));
 95:     PetscCheck(FPC, PETSC_COMM_SELF, PETSC_ERR_ARG_WRONGSTATE, "Nonlinear preconditioner has no function");
 96:     if (fnorm) PetscCall(VecNorm(FPC, NORM_2, fnorm));
 97:     PetscCall(VecCopy(FPC, F));
 98:   } else {
 99:     PetscCall(SNESGetSolution(snes->npc, &XPC));
100:     PetscCheck(XPC, PETSC_COMM_SELF, PETSC_ERR_ARG_WRONGSTATE, "Nonlinear preconditioner has no solution");
101:     PetscCall(SNESComputeFunction(snes->npc, XPC, F));
102:     if (fnorm) PetscCall(VecNorm(F, NORM_2, fnorm));
103:   }
104:   PetscFunctionReturn(PETSC_SUCCESS);
105: }