fix: sort space points before Acts seeding to ensure MT reproducibility - #2804
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wdconinc wants to merge 3 commits into
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fix: sort space points before Acts seeding to ensure MT reproducibility#2804wdconinc wants to merge 3 commits into
wdconinc wants to merge 3 commits into
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Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
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Pull request overview
This PR improves multi-thread reproducibility in the tracking seeding chain by deterministically ordering SpacePoint inputs before building the Acts space-point container and running Acts::SeedFinderOrthogonal, reducing sensitivity to input-order-dependent KDTree behavior.
Changes:
- Added a deterministic
std::stable_sortofspacePointsinTrackSeeding::processusing a lexicographic coordinate key and anObjectIDtie-breaker. - Added the necessary
<algorithm>include to support the new sort.
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| std::stable_sort(spacePoints.begin(), spacePoints.end(), [](const auto* lhs, const auto* rhs) { | ||
| const auto lhsPositionKey = std::tuple{lhs->r(), lhs->phi(), lhs->z(), lhs->x(), lhs->y()}; | ||
| const auto rhsPositionKey = std::tuple{rhs->r(), rhs->phi(), rhs->z(), rhs->x(), rhs->y()}; | ||
| if (lhsPositionKey != rhsPositionKey) { | ||
| return lhsPositionKey < rhsPositionKey; | ||
| } | ||
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| const auto lhsId = lhs->getObjectID(); | ||
| const auto rhsId = rhs->getObjectID(); | ||
| return std::tie(lhsId.collectionID, lhsId.index) < std::tie(rhsId.collectionID, rhsId.index); | ||
| }); |
SpacePoint only exposes x(), y(), z(), r(). Use (r, z, x, y) as the sort key; phi = atan2(y, x) is fully encoded by (x, y) so no sorting information is lost. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
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| auto [trk_seeds, trk_params] = output; | ||
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| std::vector<const eicrecon::SpacePoint*> spacePoints = getSpacePoints(*trk_hits); | ||
| std::stable_sort(spacePoints.begin(), spacePoints.end(), [](const auto* lhs, const auto* rhs) { |
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use a ranges version of this algorithm
Suggested change
| std::stable_sort(spacePoints.begin(), spacePoints.end(), [](const auto* lhs, const auto* rhs) { | |
| std::ranges::stable_sort(spacePoints,, [](const auto* lhs, const auto* rhs) { |
…ty (fix: iwyu) (#2812) This PR applies the include-what-you-use fixes as suggested by https://github.com/eic/EICrecon/actions/runs/30486835399. Please merge this PR into the branch `wdconinc-fix-trackseeding-sp-sort-for-mt-reproduc` to resolve failures in PR #2804. Auto-generated by [create-pull-request][1] [1]: https://github.com/peter-evans/create-pull-request Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
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Capybara summary for PR 2804
Last updated 2026-07-29T20:36-04:00 227195c |
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Briefly, what does this PR introduce? Please link to any relevant presentations or discussions.
This introduces a deterministic pre-sort of
spacePointsinTrackSeeding::processbefore constructing the Acts space-point container and callingActs::SeedFinderOrthogonal.The sort is
std::stable_sortwith lexicographic key(r, phi, z, x, y)and a finalObjectID(collectionID, index)tie-breaker for exact coordinate ties. This canonicalizes seeding input order across runs.Motivation/background:
compare-single-multi-threadedinvestigations showed ~1 ULP ST/MT differences inCentralCKFTracksUnfiltered/CentralCKFTrackParametersUnfiltereddue to ordering sensitivity in the seed/track chain.Acts::SeedFinderOrthogonaluses KDTree internals whose split behavior (std::partition) can be input-order sensitive for near-equal coordinates.wdconinc-fix-digi-determinism, commitcc20d099e).What is the urgency of this PR?
What kind of change does this PR introduce?
Please check if any of the following apply
AI usage: assisted with implementing the deterministic stable sort, preparing commit/PR text, and running targeted local build/configuration checks.