Skip to content

Detect divergence in parilu and always do the exact PCILU first #238

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
stevendargaville merged 1 commit into from
May 30, 2026
Merged

Detect divergence in parilu and always do the exact PCILU first #238

Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
89 changes: 54 additions & 35 deletions tests/ilu_factors.c
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -255,6 +255,7 @@ int main(int argc, char **args)
PetscInt max_sweeps = 100, sweep;
PetscReal parilu_tol = 1e-4;
PetscBool converged = PETSC_FALSE;
PetscBool parilu_diverged = PETSC_FALSE;
PetscBool solves_converged = PETSC_TRUE;
PetscInt jac_max_it = 1; /* Jacobi inner iterations, derived from AIR cycle complexity */

Expand Down Expand Up @@ -446,6 +447,40 @@ int main(int argc, char **args)

PetscCall(MatCreateVecs(U, &inv_dU, NULL));


PetscCall(PetscRandomCreate(PETSC_COMM_WORLD, &rnd));
PetscCall(PetscRandomSetFromOptions(rnd));
PetscCall(MatCreateVecs(A, &b_rand, &x_sol));
/* Single random rhs reused across all solves. */
PetscCall(VecSetRandom(b_rand, rnd));

/* A x = b with GMRES(30) and PETSc's built-in PCBJACOBI/ILU baseline, run
before ParILU to establish whether the problem is solvable independently
of factor quality. */
PetscCall(PetscLogStagePush(stage_A_pcilu));
{
KSP ksp_Apc;
PC pc_Apc;
PetscCall(KSPCreate(PETSC_COMM_WORLD, &ksp_Apc));
PetscCall(KSPSetType(ksp_Apc, KSPGMRES));
PetscCall(KSPGMRESSetRestart(ksp_Apc, 30));
PetscCall(KSPSetNormType(ksp_Apc, KSP_NORM_UNPRECONDITIONED));
PetscCall(KSPSetOperators(ksp_Apc, A, A));
PetscCall(KSPSetTolerances(ksp_Apc, 1e-6, 1e-50, PETSC_DEFAULT, 2000));
PetscCall(KSPGetPC(ksp_Apc, &pc_Apc));
/* PCBJACOBI's default sub-PC for AIJ blocks is PCILU(0). In serial that's
exactly PETSc's PCILU on the whole matrix; in MPI it's a per-rank ILU
inside block-Jacobi — the standard "parallel PCILU" pattern. */
PetscCall(PCSetType(pc_Apc, PCBJACOBI));
PetscCall(KSPSetOptionsPrefix(ksp_Apc, "Apc_"));
PetscCall(KSPSetFromOptions(ksp_Apc));
PetscCall(KSPSetUp(ksp_Apc));
PetscCall(KSPSolve(ksp_Apc, b_rand, x_sol));
PetscCall(ReportSolve("A x = b solve (gmres(30) + PCBJACOBI/ILU)", ksp_Apc, A, b_rand, x_sol, &solves_converged));
PetscCall(KSPDestroy(&ksp_Apc));
}
PetscCall(PetscLogStagePop());

/* ParILU sweep:
This won't necessarily converge as well as a true asynchronous (ie Gauss-Seidel) ParILU
but the benefit of this is it works with MPI parallel and in Kokkos automatically
Expand All @@ -457,7 +492,8 @@ int main(int argc, char **args)
R_L *= diag(U)^-1 (right scaling)
L += R_L (subset pattern)
U += R_U (same pattern)
*/
*/
PetscReal res_initial = -1.0;
PetscCall(PetscLogStagePush(stage_parilu));
for (sweep = 0; sweep < max_sweeps; sweep++) {
if (sweep == 0) PetscCall(MatMatMult(L, U, MAT_INITIAL_MATRIX, PETSC_DEFAULT, &M));
Expand All @@ -474,10 +510,19 @@ int main(int argc, char **args)
PetscCall(MatNorm(R_L, NORM_FROBENIUS, &rl_norm));
PetscCall(MatNorm(R_U, NORM_FROBENIUS, &ru_norm));
PetscReal res = PetscSqrtReal(rl_norm * rl_norm + ru_norm * ru_norm);
if (sweep == 0) res_initial = res;
PetscCall(PetscPrintf(PETSC_COMM_WORLD,
" ParILU sweep %3" PetscInt_FMT " stencil residual = %.6e\n",
sweep, (double)res));
if (res < threshold) { converged = PETSC_TRUE; sweep++; break; }
if (PetscIsInfOrNanReal(res) || (res_initial > 0.0 && res > 1000.0 * res_initial)) {
PetscCall(PetscPrintf(PETSC_COMM_WORLD,
" ParILU diverged at sweep %" PetscInt_FMT
": residual %.6e exceeds 1000x initial %.6e or is non-finite\n",
sweep, (double)res, (double)res_initial));
parilu_diverged = PETSC_TRUE;
break;
}

PetscCall(MatGetDiagonal(U, inv_dU));
PetscCall(VecReciprocal(inv_dU));
Expand All @@ -501,6 +546,14 @@ int main(int argc, char **args)
PetscCall(MatDestroy(&A_U));
PetscCall(VecDestroy(&inv_dU));

if (parilu_diverged) {
PetscCall(MatDestroy(&L));
PetscCall(MatDestroy(&U));
PetscCall(MatDestroy(&A));
PetscCall(PetscFinalize());
return 1;
}

/* Capture 1/diag(U_raw) and left-scale U by it (mirrors test_ilu.py).
U becomes unit-diagonal, which reduces non-normality and helps the inner
AIR solves on the U factor. L is already unit-diagonal so left-scaling by
Expand All @@ -520,16 +573,9 @@ int main(int argc, char **args)
/* U x = b same five inner PCs */
/* A x = b GMRES(30) + shell PC = U^-1 L^-1 via PCAIR inner */
/* A x = b GMRES(30) + shell PC = U^-1 L^-1 via PCJACOBI inner */
/* A x = b GMRES(30) + PETSc's built-in PCBJACOBI/ILU */
/* All factor solves use the unpreconditioned residual norm and rtol=1e-6. */
/* ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ */

PetscCall(PetscRandomCreate(PETSC_COMM_WORLD, &rnd));
PetscCall(PetscRandomSetFromOptions(rnd));
PetscCall(MatCreateVecs(A, &b_rand, &x_sol));
/* Single random rhs reused across all solves. */
PetscCall(VecSetRandom(b_rand, rnd));

/* The PCAIR Ax=b shell-PC solve below consumes inv_diag_U_raw (its destroy
callback frees it). The PCJACOBI-inner Ax=b shell solve added later also
needs the raw-diagonal compensation between L and U solves, so duplicate
Expand Down Expand Up @@ -689,36 +735,9 @@ int main(int argc, char **args)
}
PetscCall(PetscLogStagePop());

/* L and U are no longer needed past the shell-PC solves; release before the
PCILU comparison to free memory. */
PetscCall(MatDestroy(&L));
PetscCall(MatDestroy(&U));

/* A x = b with GMRES(30) and PETSc's built-in PCBJACOBI/ILU baseline. */
PetscCall(PetscLogStagePush(stage_A_pcilu));
{
KSP ksp_Apc;
PC pc_Apc;
PetscCall(KSPCreate(PETSC_COMM_WORLD, &ksp_Apc));
PetscCall(KSPSetType(ksp_Apc, KSPGMRES));
PetscCall(KSPGMRESSetRestart(ksp_Apc, 30));
PetscCall(KSPSetNormType(ksp_Apc, KSP_NORM_UNPRECONDITIONED));
PetscCall(KSPSetOperators(ksp_Apc, A, A));
PetscCall(KSPSetTolerances(ksp_Apc, 1e-6, 1e-50, PETSC_DEFAULT, 2000));
PetscCall(KSPGetPC(ksp_Apc, &pc_Apc));
/* PCBJACOBI's default sub-PC for AIJ blocks is PCILU(0). In serial that's
exactly PETSc's PCILU on the whole matrix; in MPI it's a per-rank ILU
inside block-Jacobi — the standard "parallel PCILU" pattern. */
PetscCall(PCSetType(pc_Apc, PCBJACOBI));
PetscCall(KSPSetOptionsPrefix(ksp_Apc, "Apc_"));
PetscCall(KSPSetFromOptions(ksp_Apc));
PetscCall(KSPSetUp(ksp_Apc));
PetscCall(KSPSolve(ksp_Apc, b_rand, x_sol));
PetscCall(ReportSolve("A x = b solve (gmres(30) + PCBJACOBI/ILU)", ksp_Apc, A, b_rand, x_sol, &solves_converged));
PetscCall(KSPDestroy(&ksp_Apc));
}
PetscCall(PetscLogStagePop());

int exit_code = (converged && solves_converged) ? 0 : 1;

/* Final cleanup */
Expand Down
Loading