Multi-level Algorithms for Modularity Clustering

  • Authors:
  • Andreas Noack;Randolf Rotta

  • Affiliations:
  • Brandenburg University of Technology, Cottbus, Germany 03013;Brandenburg University of Technology, Cottbus, Germany 03013

  • Venue:
  • SEA '09 Proceedings of the 8th International Symposium on Experimental Algorithms
  • Year:
  • 2009

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Abstract

Modularity is a widely used quality measure for graph clusterings. Its exact maximization is prohibitively expensive for large graphs. Popular heuristics progressively merge clusters starting from singletons (coarsening), and optionally improve the resulting clustering by moving vertices between clusters (refinement). This paper experimentally compares existing and new heuristics of this type with respect to their effectiveness (achieved modularity) and runtime. For coarsening, it turns out that the most widely used criterion for merging clusters (modularity increase) is outperformed by other simple criteria, and that a recent multi-step algorithm is no improvement over simple single-step coarsening for these criteria. For refinement, a new multi-level algorithm produces significantly better clusterings than conventional single-level algorithms. A comparison with published benchmark results and algorithm implementations shows that combinations of coarsening and multi-level refinement are competitive with the best algorithms in the literature.