perf(lindblad): store the expm generator cache as blocked flat CSC - #229
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build_mf_cols / build_orbit_rep_cols returned one Vec per column, each reserved at the full L* output count although only in-basis entries are kept. On large bases this over-reserves the cache severalfold and leaves one small allocation per basis string per expm call for the allocator to retain. The cache is now a BlockCsc: blocks of up to 4096 columns, each an exactly sized offsets/rows/vals triple (structure of arrays, 12 B per real entry instead of 16 B). CscOp::dot keeps the same per-thread column partition, so results are bit-identical. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
david-pl
approved these changes
Sep 28, 2026
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Stacked on #222 (
split/5-kossakowski).Summary
build_mf_cols/build_orbit_rep_colsreturned oneVecper column, each reserved at the full L* output count although only in-basis entries are kept. The expm generator cache is now aBlockCsc: blocks of up to 4096 columns, each an exactly sizedoffsets/rows/valstriple (structure of arrays, 12 B per real entry instead of 16 B).CscOp::dotkeeps the same per-thread column partition, so results are bit-identical.Single commit,
crates/ppvm-lindblad/src/mf_expm.rsonly.Measurements
pc_stepon the two-leg XY ladder with a local probe (not part of this PR): L = 41 rungs (N = 82),max_basis = 2^18,admit_basis = 3·2^18, dt = 0.1, 25 steps, 4 threads,drop_tol = 0. Apple M4 MacBook Air (fanless, so wall times are only comparable within a rep). Max RSS from/usr/bin/time -l; live-heap peak from a counting global allocator./usr/bin/time -l) drops by about 3–13%. With the macOS system allocator, RSS is not reproducible (768–1237 MiB for the same binary), so the effect cannot be resolved there.Tests:
cargo test -p ppvm-lindbladpasses (8/8) with this change stacked together with the skip-empty-hop2 PR; not yet run on this branch alone (CI will).🤖 Generated with Claude Code