Isolation concepts for enumerating dense subgraphs

  • Authors:
  • Christian Komusiewicz;Falk Hüffner;Hannes Moser;Rolf Niedermeier

  • Affiliations:
  • Institut für Informatik, Friedrich-Schiller-Universität Jena, Jena, Germany;Institut für Informatik, Friedrich-Schiller-Universität Jena, Jena, Germany;Institut für Informatik, Friedrich-Schiller-Universität Jena, Jena, Germany;Institut für Informatik, Friedrich-Schiller-Universität Jena, Jena, Germany

  • Venue:
  • COCOON'07 Proceedings of the 13th annual international conference on Computing and Combinatorics
  • Year:
  • 2007

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Abstract

In a graph G = (V,E), a vertex subset S ⊆ V of size k is called c-isolated if it has less than c ċ k outgoing edges. We repair a nontrivially flawed algorithm for enumerating all c-isolated cliques due to Ito et al. [European Symposium on Algorithms 2005] and obtain an algorithm running in O(4c ċ c4 ċ |E|) time. We describe a speedup trick that also helps parallelizing the enumeration. Moreover, we introduce a more restricted and a more general isolation concept and show that both lead to faster enumeration algorithms. Finally, we extend our considerations to s-plexes (a relaxation of the clique notion), pointing out a W[1]-hardness result and providing a fixed-parameter algorithm for enumerating isolated s-plexes.