A Local Algorithm for Finding Dense Subgraphs

We present a local algorithm for finding dense subgraphs of bipartite graphs, according to the definition of density proposed by Kannan and Vinay. Our algorithm takes as input a bipartite graph with a specified starting vertex, and attempts to find a dense subgraph near that vertex. We prove that for any subgraph S with k vertices and density theta, there are a significant number of starting vertices within S for which our algorithm produces a subgraph S' with density theta / O(log n) on at most O(D k^2) vertices, where D is the maximum degree. The running time of the algorithm is O(D k^2), independent of the number of vertices in the graph.