Correlation Clustering (SCC)

Original Repository: https://github.com/ScalableCorrelationClustering/ScalableCorrelationClustering

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Overview

Correlation clustering operates on graphs with signed edge weights: positive weights indicate similarity, negative weights indicate dissimilarity. The goal is to partition the vertex set into an arbitrary number of clusters that minimizes the total disagreements -- positive edges that cross cluster boundaries plus negative edges that remain within the same cluster.

Unlike standard clustering, the number of clusters is not fixed a priori but determined automatically by the optimization. CHSZLabLib provides two SCC variants:

Method	Description
correlation_clustering()	Multilevel label propagation (fast)
evolutionary_correlation_clustering()	Memetic evolutionary algorithm (higher quality, longer runtime)

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Decomposition.correlation_clustering()

Signature

Decomposition.correlation_clustering(
    g: Graph,
    seed: int = 0,
    time_limit: float = 0,
) -> CorrelationClusteringResult

Parameters

Parameter	Type	Default	Description
g	Graph	required	Input graph with signed edge weights. Positive = similarity, negative = dissimilarity.
seed	int	0	Random seed for reproducibility.
time_limit	float	0	Time limit in seconds (0 = no limit).

Returns

CorrelationClusteringResult

Field	Type	Description
edge_cut	int	Number of disagreements.
num_clusters	int	Number of clusters found.
assignment	np.ndarray (int32)	Cluster ID for each node (0-indexed).

Example

from chszlablib import Graph, Decomposition

g = Graph(num_nodes=4)
g.add_edge(0, 1, weight=1)    # similar
g.add_edge(1, 2, weight=-1)   # dissimilar
g.add_edge(2, 3, weight=1)    # similar
g.add_edge(0, 3, weight=-1)   # dissimilar
g.finalize()

result = Decomposition.correlation_clustering(g, seed=42)
print(f"Clusters: {result.num_clusters}, disagreements: {result.edge_cut}")

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Decomposition.evolutionary_correlation_clustering()

A higher-quality variant that uses a population-based memetic evolutionary algorithm with recombination and multilevel local search.

Signature

Decomposition.evolutionary_correlation_clustering(
    g: Graph,
    seed: int = 0,
    time_limit: float = 5.0,
) -> CorrelationClusteringResult

Parameters

Parameter	Type	Default	Description
g	Graph	required	Input graph with signed edge weights.
seed	int	0	Random seed for reproducibility.
time_limit	float	5.0	Time budget in seconds for the evolutionary search.

Returns

CorrelationClusteringResult (same fields as above).

Example

from chszlablib import Graph, Decomposition

g = Graph.from_metis("signed_graph.graph")

# Fast version
fast = Decomposition.correlation_clustering(g, seed=42)
print(f"Fast: {fast.num_clusters} clusters, {fast.edge_cut} disagreements")

# Evolutionary refinement
evo = Decomposition.evolutionary_correlation_clustering(g, time_limit=30.0, seed=42)
print(f"Evo:  {evo.num_clusters} clusters, {evo.edge_cut} disagreements")

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Performance Disclaimer

This Python interface wraps the SCC C++ library via pybind11. While convenient for prototyping and integration into Python workflows, there is inherent overhead from the Python/C++ boundary and data conversion. For maximum performance on large-scale instances, use the original C++ implementation directly from the SCC repository.

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References

@inproceedings{DBLP:conf/alenex/HausbergerF025,
  author    = {Felix Hausberger and Marcelo Fonseca Faraj and Christian Schulz},
  title     = {Scalable Multilevel and Memetic Signed Graph Clustering},
  booktitle = {Proceedings of the 27th Symposium on Algorithm Engineering and Experiments,
               {ALENEX} 2025},
  pages     = {81--94},
  publisher = {{SIAM}},
  year      = {2025},
  doi       = {10.1137/1.9781611978339.7}
}