Fix MLMG boundary coefficients and improve PFMG stability#237
Merged
jameslehoux merged 2 commits intoworkingfrom Apr 1, 2026
Merged
Fix MLMG boundary coefficients and improve PFMG stability#237jameslehoux merged 2 commits intoworkingfrom
jameslehoux merged 2 commits intoworkingfrom
Conversation
added 2 commits
April 1, 2026 10:31
PFMG (geometric multigrid) produces NaN on the uniform block test case and MLMG doesn't converge accurately. Replace with BiCGSTAB and GMRES which are proper Krylov solvers supported by HYPRE. https://claude.ai/code/session_01RKnn97qiD7sbCeABHH3eQk
MLMG: The B-coefficients (face diffusivities) were computed via harmonic mean of adjacent cell-centred values, but physical boundary ghost cells had D=0 (default). This made boundary face B=0, preventing Dirichlet BCs from being enforced. Fix: extrapolate D into boundary ghost cells before computing face coefficients. PFMG: Increase pre/post relaxation sweeps from 1 to 2 and set relaxation type to weighted Jacobi (type 2) for better stability on uniform/homogeneous problems where the default red-black Gauss-Seidel can produce NaN residuals. Benchmark: restore PFMG and MLMG to the solver list, add BiCGSTAB and GMRES for broader coverage. https://claude.ai/code/session_01RKnn97qiD7sbCeABHH3eQk
Performance Benchmark Results
Fastest solver: mlmg at 64³ (0.2653s) Benchmark: uniform block (analytical τ = (N-1)/N) |
Code Coverage ReportGenerated by CI — coverage data from gcovr |
Codecov Report❌ Patch coverage is
📢 Thoughts on this report? Let us know! |
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
1 participant
Add this suggestion to a batch that can be applied as a single commit.This suggestion is invalid because no changes were made to the code.Suggestions cannot be applied while the pull request is closed.Suggestions cannot be applied while viewing a subset of changes.Only one suggestion per line can be applied in a batch.Add this suggestion to a batch that can be applied as a single commit.Applying suggestions on deleted lines is not supported.You must change the existing code in this line in order to create a valid suggestion.Outdated suggestions cannot be applied.This suggestion has been applied or marked resolved.Suggestions cannot be applied from pending reviews.Suggestions cannot be applied on multi-line comments.Suggestions cannot be applied while the pull request is queued to merge.Suggestion cannot be applied right now. Please check back later.
MLMG: The B-coefficients (face diffusivities) were computed via
harmonic mean of adjacent cell-centred values, but physical boundary
ghost cells had D=0 (default). This made boundary face B=0, preventing
Dirichlet BCs from being enforced. Fix: extrapolate D into boundary
ghost cells before computing face coefficients.
PFMG: Increase pre/post relaxation sweeps from 1 to 2 and set
relaxation type to weighted Jacobi (type 2) for better stability on
uniform/homogeneous problems where the default red-black Gauss-Seidel
can produce NaN residuals.
Benchmark: restore PFMG and MLMG to the solver list, add BiCGSTAB
and GMRES for broader coverage.