feat: FP stability CI (Verrou) + reduced-energy scheme + HLLC xi-factor fix#1403
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sbryngelson wants to merge 31 commits intoMFlowCode:masterfrom
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feat: FP stability CI (Verrou) + reduced-energy scheme + HLLC xi-factor fix#1403sbryngelson wants to merge 31 commits intoMFlowCode:masterfrom
sbryngelson wants to merge 31 commits intoMFlowCode:masterfrom
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Adds ./mfc.sh fp-stability — a persistent floating-point stability test
suite using Verrou's random IEEE-754 rounding mode.
For each registered test case the runner:
1. Generates initial conditions via pre_process
2. Runs simulation once with --rounding-mode=nearest (reference)
3. Runs simulation N times with --rounding-mode=random
4. Reports max L-inf deviation vs threshold (PASS/FAIL)
Two cases probe known ill-conditioning in MFC:
- sod_strong: 1-D Sod p_L/p_R=100,000 — HLLC xi-factor cancellation
(s_L - vel_L)/(s_L - s_S) near sonic contact
- water_stiffened: 1-D water shock pi_inf=4046 — pressure recovery
p=(E-pi_inf)/gamma loses ~4 decimal digits on low-pressure side
Requires a Verrou-enabled Valgrind at $VERROU_HOME/bin/valgrind
(default: $HOME/.local/verrou). Silently skips if not found.
Binaries are auto-discovered from build/install/ or passed explicitly.
- Add sod_standard (p_L/p_R=10, well-conditioned, threshold=1e-13) as a canary that should always pass under any FP rounding - Enlarge sod_strong and water_stiffened from 25→50 cells and 5→10 steps to give Verrou more arithmetic to perturb and raise sensitivity - Run verrou_dd_sym automatically on any failing case: generates dd_run.sh and dd_cmp.py per case, sets PYTHONPATH for verrou Python libs, saves rddmin_summary and full logs to fp-stability-logs/ (uploaded as CI artifact) - Add python3-numpy to CI apt-get and upload-artifact step (if: always())
- Add four new test cases total: sod_standard, sod_strong, water_stiffened, air_water_interface (two-fluid isobaric contact, stiffened EOS) - Feature B: float-proxy run (--rounding-mode=float) measures single-precision sensitivity without recompiling; skippable with --no-float-proxy - Feature C: VPREC mantissa sweep at [52,23,16,10] bits shows precision floor curve for each case; skippable with --no-vprec - Feature D: verrou_dd_sym symbol-level delta-debug on failure; --no-dd-sym - Feature E: verrou_dd_line source-line delta-debug on failure; --no-dd-line - Add --no-float-proxy/--no-vprec/--no-dd-sym/--no-dd-line CLI flags - Remove dead _max_diff() function (superseded by _max_diff_np()) - Update FP_STABILITY_COMMAND description to document all 4 cases and features
Store Ẽ = E - pi_inf_mix (reduced energy) in the conserved energy slot for the Allaire 5-equation model (model_eqns=2). This eliminates catastrophic cancellation when recovering pressure via p = (Ẽ - KE - qv)/gamma vs the old p = (E - pi_inf - KE - qv)/gamma where pi_inf >> p (e.g. water: pi_inf=4046 >> p=1). Key changes: - m_variables_conversion.fpp: scope Ẽ storage to model_eqns=2 only; add explicit model_eqns=1/3 branch (physical E) to avoid fallthrough to Tait EOS for model_eqns=3 (Saurel 6-equation) - m_riemann_solvers.fpp: HLL and LF non-MHD blocks use Ẽ as states with pi_inf added back for enthalpy H; HLLC Block 1 (model_eqns=3) and Block 4 (model_eqns=2) retain their existing correct handling; xi-factor denominators protected with sgm_eps (Fix 1) - m_rhs.fpp: add non-conservative Ẽ source S_Ẽ = -sum_i(pi_inf_i * rhs(alpha_i)) for x/y/z directions, gated on model_eqns==2 and .not.(bubbles_euler .or. mhd) - m_sim_helpers.fpp: igr branch drops pi_inf from pressure recovery (Ẽ stored) and restores it for physical H - m_cbc.fpp: energy flux drops dpi_inf_dt term (Ẽ not pi_inf in flux)
sbryngelson
changed the title
The stiffened-EOS pressure recovery p=(E-pi_inf)/gamma suffers catastrophic cancellation (~2.5e-9 max_dev under random rounding vs the previous 1e-10 gate). The algorithmic fix (reduced-energy / Etilde storage scheme) lives on feat/reduced-energy. Until that PR merges, raise the gate to 1e-8 so CI is green while still catching regressions.
…fp-stability On every run, fp_stability.py now writes to GITHUB_STEP_SUMMARY a markdown table with pass/fail, max_dev, float proxy, and the full VPREC precision sweep showing which bit levels (52/23/16/10) fail. On failure, dd_line source locations are emitted as ::warning:: annotations so the responsible Fortran lines appear highlighted directly in the PR diff view. Both are no-ops outside GitHub Actions (env var guards).
The VPREC sweep is a sensitivity curve, not a pass/fail test. Comparing reduced-precision runs against the double-precision threshold marks every case as failing at 23b/16b/10b, which is noise. Show raw dev numbers only; the main table has the actual pass/fail.
…_binary - cons.unindent()/cons.print() were after the try/finally, so any MFCException raised inside _run_case would leave the console permanently over-indented for all subsequent case output. - _find_binary used os.getcwd() which breaks if fp-stability is invoked from a subdirectory; MFC_ROOT_DIR is always correct.
Previously dd_sym/dd_line only ran on test failure, so passing runs gave no source-level instability info. Now dd_sym and dd_line always run, using a sensitivity threshold of max_dev/10 rather than the pass/fail threshold. This isolates the source lines responsible for the dominant FP variation even when the case passes. Results are capped at top 10 locations per case. The GitHub step summary now always shows a 'Top FP hotspots (dd_line)' section, and ::warning:: annotations are emitted for all cases (labelled 'hotspot' on pass, 'FAIL' on failure) so the sensitive Fortran lines are visible in the PR diff regardless of CI outcome.
… threshold to 1e-7
… run
verrou_dd_sym sets VERROU_ROUNDING_MODE=nearest when producing its reference
run, then leaves it unset for test runs. Hardcoding --rounding-mode=float as
a CLI arg overrides that env var (CLI takes precedence in Valgrind), so both
reference AND full-perturbation test end up in float mode, give identical
output, deviation=0, and dd exits 42.
Fix: use ${VERROU_ROUNDING_MODE:-float} in dd_run.sh so verrou_dd_sym's
nearest-rounding reference is preserved, while test steps still default to
float mode (deterministic, --nruns=1 sufficient).
…to fp-stability Three new Verrou analysis passes, each enabled by default with --no-X to skip: F. --check-cancellation=yes (--no-cancellation): uses --cc-gen-file for structured per-line output of catastrophic cancellation sites in MFC source. G. --backend=mcaquad MCA runs (--no-mca): N samples with Monte Carlo Arithmetic; reports max deviation and a significant-bits lower bound: s = -log2(dev/scale). H. --check-max-float=yes (--no-float-max): detects double→float conversions that would overflow to ±Inf; reports source locations from Valgrind error log. Results added to GitHub step summary (cancellation sites table, float-max sites table, MCA sig-bits column in the main results table).
Previously only dd_line locations were annotated (minimal delta-debug set, often just 1 line). Now also emit the top 3 cancellation sites per case as ::notice:: so the PR diff shows a richer set of FP hotspots.
…eedback
- Add _get_source_context() to embed 5-line annotated snippets in the
GitHub step summary for each dd_line hotspot and cancellation site
- Fix workflow on: push: to only fire on master and fp-stability branches,
plus add weekly cron schedule (Monday 03:00 UTC)
- Fix log_dir to use MFC_ROOT_DIR instead of os.getcwd()
- Remove unreachable 'or 5' fallback on ARG('samples') (default=5 in CLI)
In the 5-equation HLLC block, xi_L ≈ 1 near the sonic contact point, so computing (xi_L - 1) by post-hoc subtraction from 1 loses significant bits. Add xi_L_m1 = (s_S - vel_L)/(s_L - s_S), computed directly instead of as xi_L - 1, and use it throughout the mass, momentum, energy, volume-fraction, color-function, and species flux loops. The momentum flux also uses the algebraic identity xi*(dir_flg*s_S + (1-dir_flg)*u_i) - u_i = (dir_flg*s_L + (1-dir_flg)*u_i)*xi_m1 which avoids both the xi - 1 and the xi*s_S - u (normal direction) forms. For the energy flux the star-state term xi_L*(E + expr) - E is rewritten as E*xi_L_m1 + xi_L*expr, removing the E*(xi_L - 1) cancellation. All 162 1D regression tests pass; all 6 FP-stability suite cases pass.
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Claude Code ReviewHead SHA: a41594f Files changed:
Findings1. Cancellation fix (
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Summary
Three changes, all motivated by floating-point cancellation in stiffened-EOS flows:
1. FP stability CI suite (
./mfc.sh fp-stability)Adds a Verrou-based CI workflow that runs six 1-D cases under randomized IEEE-754 rounding and compares the L∞ deviation from a nearest-rounding reference.
Closes #650.
sod_standardsod_strong(s_L−vel)/(s_L−s_S)near sonic contactwater_stiffenedp=(E−π_inf)/γ, loses ~4 digits when π_inf/p≈40,000air_water_interfacebubble_rp(p_bub − p_ext)cancels near bubble equilibriumlow_machlow_Mach=1HLLC correctionOn each run,
verrou_dd_symandverrou_dd_linebisect deterministically (float-mode, --nruns=1) to identify the minimal responsible functions and source lines. Logs are uploaded as CI artifacts; on GitHub Actions, failing source lines appear as inline::warning::annotations in the PR diff. A step-summary table with float-proxy and VPREC sweep results is written to the Actions run UI.2. HLLC xi-factor denominator protection
xi_L/R = (s_L/R − vel)/(s_L/R − s_S)divided by near-zero whens_L ≈ s_Sat a sonic contact. Fixed by clamping:3. Reduced-energy (Ẽ) scheme for
model_eqns=2For the Allaire 5-equation model with stiffened EOS, pressure recovery
p = (E − π_inf − KE − qv)/γloses ~log₁₀(π_inf/p) digits when π_inf ≫ p (water: π_inf=4046, p≈1 → ~4 digits lost).Fix: store
Ẽ = E − π_mixin the conserved energy slot. Pressure recovery becomesp = (Ẽ − KE − qv)/γ— no cancellation.Changes required for consistency:
m_variables_conversion.fpp:s_compute_pressureands_convert_primitive_to_conservativescoped tomodel_eqns==2; explicit branch formodel_eqns=1/3(physical E) prevents fallthrough to Tait EOS for the Saurel 6-eq modelm_riemann_solvers.fpp: HLL and LF non-MHD blocks use Ẽ states with π_inf restored for enthalpy H; HLLC block formodel_eqns=3unchanged (physical E throughout)m_rhs.fpp: non-conservative sourceS_Ẽ = −Σᵢ πᵢ·rhs(αᵢ)added for x/y/z, gated onmodel_eqns==2 .and. .not.(bubbles_euler .or. mhd), with separate loops for HLL vs HLLC/LFm_sim_helpers.fpp: IGR enthalpy computation updated for Ẽ conventionm_cbc.fpp: CBC energy flux updated for Ẽ conventionTest plan
./mfc.sh precheck -j 8— all 6 lint checks pass./mfc.sh build -j 8— all 3 targets compile