feat(clustering): Louvain community detection - #7
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Add LouvainClustering implementing ClusteringAlgorithm<V> in org.jgrapht.alg.clustering: alternating local-moving and aggregation phases that greedily maximise modularity, with weighted/self-loop handling and modularity conventions matching UndirectedModularityMeasurer (reused for getModularity()). Constructors mirror LabelPropagationClustering ((graph), (graph, rng), (graph, rng, tolerance)). - 15 JUnit5 tests: cliques->2, ring->3, complete->1 (Q=0), weighted, seed determinism, single/empty/isolated, self-loops, random partition-validity, getModularity vs measurer, beats all-singletons. - JMH benchmark (perf/clustering) vs LabelPropagation and GreedyModularity on planted-partition graphs; export the new perf package(s) in the surefire argLine, matching the existing per-package pattern. checkstyle clean (etc/jgrapht_checks.xml); javadoc clean. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
…weights Adversarial review follow-ups on the Louvain PR: - Zero-weight edges (2m == 0) made getModularity() return NaN because the modularity guard tested edgeSet().isEmpty() rather than the actual total weight. Guard on totalWeight > 0 instead; return 0 otherwise. - Reject negative edge weights with IllegalArgumentException at compute time (modularity is undefined for negative weights), documented on the class. - Replace the circular getModularityMatchesMeasurer test (getModularity delegates to the measurer) with a pinned exact value Q = 11/26 for the two-K4-plus-bridge graph; add regressions for zero-weight (no NaN) and negative-weight (throws). 17/17 tests pass; checkstyle clean. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
This was referenced May 30, 2026
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Superseded by #9 — Louvain + Leiden combined into a single clustering PR. |
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Self-review PR (fork only — not for upstream; Louvain holds for a
jgrapht-devsignal first per project cadence).What
LouvainClustering<V,E>inorg.jgrapht.alg.clustering, implementingClusteringAlgorithm<V>.Alternating local-moving + aggregation phases greedily maximising modularity; weighted/self-loop
aware; modularity conventions match
UndirectedModularityMeasurer(reused forgetModularity()).Constructors mirror
LabelPropagationClustering:(graph),(graph, rng),(graph, rng, tolerance).Tests — 15/15 green
cliques→2, ring→3, complete→1 (Q=0), weighted, seed determinism, single/empty/isolated,
self-loops, random partition-validity ×20,
getModularityvs measurer, beats all-singletons.Benchmark (
perf/clustering, planted partitions, in-process forks=0)Louvain ≈ LabelPropagation cost while directly optimising modularity; 5–10× faster than
GreedyModularity and scales far better.
pom.xmlexports the newperf.clusteringpackage(s)in the surefire argLine (matches the documented per-package pattern).
Gates
checkstyle clean (
etc/jgrapht_checks.xml), javadoc clean. Companion/clustering/visualization added in jgrapht-algo-visualization (separate repo). Dev-list draft prepared.
Review focus
UndirectedModularityMeasurerRandom🤖 Generated with Claude Code