/*
Performs the FAS coarse correction as:
fine problem: F(x) = b
coarse problem: F^c(x^c) = b^c
b^c = F^c(Rx) - R(F(x) - b)
*/
PetscErrorCode SNESFASCoarseCorrection(SNES snes, Vec X, Vec F, Vec X_new)
{
PetscErrorCode ierr;
Vec X_c, Xo_c, F_c, B_c;
SNESConvergedReason reason;
SNES next;
Mat restrct, interpolate;
SNES_FAS *fasc;
PetscFunctionBegin;
ierr = SNESFASCycleGetCorrection(snes, &next);CHKERRQ(ierr);
if (next) {
fasc = (SNES_FAS*)next->data;
ierr = SNESFASCycleGetRestriction(snes, &restrct);CHKERRQ(ierr);
ierr = SNESFASCycleGetInterpolation(snes, &interpolate);CHKERRQ(ierr);
X_c = next->vec_sol;
Xo_c = next->work[0];
F_c = next->vec_func;
B_c = next->vec_rhs;
if (fasc->eventinterprestrict) {ierr = PetscLogEventBegin(fasc->eventinterprestrict,0,0,0,0);CHKERRQ(ierr);}
ierr = SNESFASRestrict(snes,X,Xo_c);CHKERRQ(ierr);
/* restrict the defect: R(F(x) - b) */
ierr = MatRestrict(restrct, F, B_c);CHKERRQ(ierr);
if (fasc->eventinterprestrict) {ierr = PetscLogEventEnd(fasc->eventinterprestrict,0,0,0,0);CHKERRQ(ierr);}
if (fasc->eventresidual) {ierr = PetscLogEventBegin(fasc->eventresidual,0,0,0,0);CHKERRQ(ierr);}
/* F_c = F^c(Rx) - R(F(x) - b) since the second term was sitting in next->vec_rhs */
ierr = SNESComputeFunction(next, Xo_c, F_c);CHKERRQ(ierr);
if (fasc->eventresidual) {ierr = PetscLogEventEnd(fasc->eventresidual,0,0,0,0);CHKERRQ(ierr);}
/* solve the coarse problem corresponding to F^c(x^c) = b^c = F^c(Rx) - R(F(x) - b) */
ierr = VecCopy(B_c, X_c);CHKERRQ(ierr);
ierr = VecCopy(F_c, B_c);CHKERRQ(ierr);
ierr = VecCopy(X_c, F_c);CHKERRQ(ierr);
/* set initial guess of the coarse problem to the projected fine solution */
ierr = VecCopy(Xo_c, X_c);CHKERRQ(ierr);
/* recurse to the next level */
ierr = SNESSetInitialFunction(next, F_c);CHKERRQ(ierr);
ierr = SNESSolve(next, B_c, X_c);CHKERRQ(ierr);
ierr = SNESGetConvergedReason(next,&reason);CHKERRQ(ierr);
if (reason < 0 && reason != SNES_DIVERGED_MAX_IT) {
snes->reason = SNES_DIVERGED_INNER;
PetscFunctionReturn(0);
}
/* correct as x <- x + I(x^c - Rx)*/
ierr = VecAXPY(X_c, -1.0, Xo_c);CHKERRQ(ierr);
if (fasc->eventinterprestrict) {ierr = PetscLogEventBegin(fasc->eventinterprestrict,0,0,0,0);CHKERRQ(ierr);}
ierr = MatInterpolateAdd(interpolate, X_c, X, X_new);CHKERRQ(ierr);
if (fasc->eventinterprestrict) {ierr = PetscLogEventEnd(fasc->eventinterprestrict,0,0,0,0);CHKERRQ(ierr);}
}
PetscFunctionReturn(0);
}
/*
The additive cycle looks like:
xhat = x
xhat = dS(x, b)
x = coarsecorrection(xhat, b_d)
x = x + nu*(xhat - x);
(optional) x = uS(x, b)
With the coarse RHS (defect correction) as below.
*/
PetscErrorCode SNESFASCycle_Additive(SNES snes, Vec X)
{
Vec F, B, Xhat;
Vec X_c, Xo_c, F_c, B_c;
PetscErrorCode ierr;
SNESConvergedReason reason;
PetscReal xnorm, fnorm, ynorm;
PetscBool lssuccess;
SNES next;
Mat restrct, interpolate;
SNES_FAS *fas = (SNES_FAS*)snes->data,*fasc;
PetscFunctionBegin;
ierr = SNESFASCycleGetCorrection(snes, &next);CHKERRQ(ierr);
F = snes->vec_func;
B = snes->vec_rhs;
Xhat = snes->work[1];
ierr = VecCopy(X, Xhat);CHKERRQ(ierr);
/* recurse first */
if (next) {
fasc = (SNES_FAS*)next->data;
ierr = SNESFASCycleGetRestriction(snes, &restrct);CHKERRQ(ierr);
ierr = SNESFASCycleGetInterpolation(snes, &interpolate);CHKERRQ(ierr);
if (fas->eventresidual) {ierr = PetscLogEventBegin(fas->eventresidual,0,0,0,0);CHKERRQ(ierr);}
ierr = SNESComputeFunction(snes, Xhat, F);CHKERRQ(ierr);
if (fas->eventresidual) {ierr = PetscLogEventEnd(fas->eventresidual,0,0,0,0);CHKERRQ(ierr);}
ierr = VecNorm(F, NORM_2, &fnorm);CHKERRQ(ierr);
X_c = next->vec_sol;
Xo_c = next->work[0];
F_c = next->vec_func;
B_c = next->vec_rhs;
ierr = SNESFASRestrict(snes,Xhat,Xo_c);CHKERRQ(ierr);
/* restrict the defect */
ierr = MatRestrict(restrct, F, B_c);CHKERRQ(ierr);
/* solve the coarse problem corresponding to F^c(x^c) = b^c = Rb + F^c(Rx) - RF(x) */
if (fasc->eventresidual) {ierr = PetscLogEventBegin(fasc->eventresidual,0,0,0,0);CHKERRQ(ierr);}
ierr = SNESComputeFunction(next, Xo_c, F_c);CHKERRQ(ierr);
if (fasc->eventresidual) {ierr = PetscLogEventEnd(fasc->eventresidual,0,0,0,0);CHKERRQ(ierr);}
ierr = VecCopy(B_c, X_c);CHKERRQ(ierr);
ierr = VecCopy(F_c, B_c);CHKERRQ(ierr);
ierr = VecCopy(X_c, F_c);CHKERRQ(ierr);
/* set initial guess of the coarse problem to the projected fine solution */
ierr = VecCopy(Xo_c, X_c);CHKERRQ(ierr);
/* recurse */
ierr = SNESSetInitialFunction(next, F_c);CHKERRQ(ierr);
ierr = SNESSolve(next, B_c, X_c);CHKERRQ(ierr);
/* smooth on this level */
ierr = SNESFASDownSmooth_Private(snes, B, X, F, &fnorm);CHKERRQ(ierr);
ierr = SNESGetConvergedReason(next,&reason);CHKERRQ(ierr);
if (reason < 0 && reason != SNES_DIVERGED_MAX_IT) {
snes->reason = SNES_DIVERGED_INNER;
PetscFunctionReturn(0);
}
/* correct as x <- x + I(x^c - Rx)*/
ierr = VecAYPX(X_c, -1.0, Xo_c);CHKERRQ(ierr);
ierr = MatInterpolate(interpolate, X_c, Xhat);CHKERRQ(ierr);
/* additive correction of the coarse direction*/
ierr = SNESLineSearchApply(snes->linesearch, X, F, &fnorm, Xhat);CHKERRQ(ierr);
ierr = SNESLineSearchGetSuccess(snes->linesearch, &lssuccess);CHKERRQ(ierr);
if (!lssuccess) {
if (++snes->numFailures >= snes->maxFailures) {
snes->reason = SNES_DIVERGED_LINE_SEARCH;
PetscFunctionReturn(0);
}
}
ierr = SNESLineSearchGetNorms(snes->linesearch, &xnorm, &snes->norm, &ynorm);CHKERRQ(ierr);
} else {
ierr = SNESFASDownSmooth_Private(snes, B, X, F, &snes->norm);CHKERRQ(ierr);
}
PetscFunctionReturn(0);
}
PETSC_EXTERN void PETSC_STDCALL snesfascyclegetinterpolation_(SNES snes,Mat *mat, int *__ierr ){
*__ierr = SNESFASCycleGetInterpolation(
(SNES)PetscToPointer((snes) ),mat);
}
