A local algorithm for finding dense subgraphs

  • Authors:
  • Reid Andersen

  • Affiliations:
  • Microsoft Research, Redmond, WA

  • Venue:
  • ACM Transactions on Algorithms (TALG)
  • Year:
  • 2010

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Abstract

We describe a local algorithm for finding subgraphs with high density, according to a measure of density introduced by Kannan and Vinay [1999]. The algorithm takes as input a bipartite graph G, a starting vertex v, and a parameter k, and outputs an induced subgraph of G. It is local in the sense that it does not examine the entire input graph; instead, it adaptively explores a region of the graph near the starting vertex. The running time of the algorithm is bounded by O(Δ k2), which depends on the maximum degree Δ, but is otherwise independent of the graph. We prove the following approximation guarantee: for any subgraph S with k′ vertices and density θ, there exists a set S′ ⊆ S for which the algorithm outputs a subgraph with density Ω(θ/log Δ) whenever v ∈ S′ and k ≥ k′. We prove that S′ contains at least half of the edges in S.