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METIS_OPTION_NSEPS (candidate separators per split) is the one NodeND knob that reproducibly improves the ACOPF KKT orderings: on kkt_pglib_opf_case78484_epigrids_condensed_10 (n = 157k), nd_nseps = 4 gives nnz(L) 14.42M vs 14.76M (-2.3%), factorization flops -6.7%, and the PR #107 fused refactorization 30.1 ms vs 32.1 ms (-6.2%, interleaved A/B on a GV100, correctness-gated) at the same schedule depth. The ordering itself runs ~2x slower, so the default stays at the METIS default (-1); the option pays off when one symbolic analysis is reused across many factorizations and is exposed like nd_ubfactor. ND_PROVIDER gains a third argument (values < 1 fall back to the library default); validated like the other config ints and covered in test_options and test_symbolic_etree.
sshin23
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Oct 13, 2026
…ering knobs, division-free Cholesky, GV100 record (#126) Device-built symbolic maps, the nd_nseps/nd_seed ordering parameters, the division-free Cholesky column step, the fused factorization/solve pipeline (src/fused.jl) with its no-pivot LDL mode and per-architecture tuning, the MadNLP package extension (exported SDSSolver with sds_factorization = :ldl and true inertia; no-pivot LDL disables 2x2 pivot-pair detection), the CPU fast path and HSL reference benches, the fresh-machine @sds workflow, and the campaign write-ups. Full validation record in the PR body. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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What
Exposes
METIS_OPTION_NSEPS(number of candidate separators METIS evaluates per split, keeping the best) as a cuDSS-style config parameternd_nseps, next tond_ubfactor. Default-1keeps the METIS default; values ≥ 1 are passed through, values < 1 fall back to the default.Why
Follow-up to the #107 ordering study:
nsepsis the one NodeND knob that reproducibly improves the ACOPF KKT orderings. Onkkt_pglib_opf_case78484_epigrids_condensed_10(n = 157k, the 78k-bus condensed KKT),nd_nseps = 4vs the default:GPU numbers are interleaved A/B medians, correctness-gated (info 0, factor delta ~3e-10 vs stock, matching residuals). The ordering itself roughly doubles in cost, so this stays opt-in: it pays when one symbolic analysis is reused across many factorizations (interior-point refactorization loops), which is the MadNLP usage pattern.
How
Optionsfield +ParameterSpec+ validation, mirroringnd_ubfactorND_PROVIDERcontract gains a third argument; the Metis extension passesnsepstoCliqueTrees.METIStest_options(roundtrip, type error, out-of-range) andtest_symbolic_etree(provider passthrough + fallback)Tests:
test_options+test_symbolic_etreeon CPU, 1658 pass. CUDA: pending CI.🤖 Generated with Claude Code