Fix duplicate-cluster trigger to require >=2 kept candidates#327
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…llow-up) PR #282 added a post-prune diversity step that fires when "all kept neighbors share the same distance". The original guard `!result.empty()` is also satisfied by `result.size() == 1`, because `all_duplicates` stays trivially true when only one candidate has been pushed into `result`. This causes the branch to fire on nodes whose alpha-pruning has collapsed `result` to a single retained neighbor, replacing that sole nearest-neighbor edge with a longer "diversity" edge -- which is unrelated to duplicate clusters. Restrict the trigger to `result.size() >= 2` so it only activates when two or more retained candidates actually share the same distance, matching the intent described in PR #282 / issue #80. Empirical impact (sift-scaled, ws=64, deg=64, pool=32, alpha=1.2, L2): - Pre-#282 baseline: recall = 0.925 - Post-#282 (current behavior): recall = 0.945 (434 triggers, 184 replacements -- all from result.size()==1) - Post-#282 + this fix (result.size() >= 2): recall = 0.925 (0 triggers, 0 replacements -- no real duplicate clusters present) This restores the documented baseline for sift-scaled CI while keeping the genuine duplicate-cluster handling for datasets that actually contain co-located vectors (e.g. issue #80 reproducer).
ethanglaser
approved these changes
May 5, 2026
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PR #282 added a post-prune diversity step that fires when "all kept neighbors share the same distance". The original guard
!result.empty()is also satisfied byresult.size() == 1, becauseall_duplicatesstays trivially true when only one candidate has been pushed intoresult. This causes the branch to fire on nodes whose alpha-pruning has collapsedresultto a single retained neighbor, replacing that sole nearest-neighbor edge with a longer "diversity" edge -- which is unrelated to duplicate clusters.Restrict the trigger to
result.size() >= 2so it only activates when two or more retained candidates actually share the same distance, matching the intent described in PR #282 / issue #80.