Sparsest cuts and concurrent flows in product graphs

  • Authors:
  • Paul Bonsma

  • Affiliations:
  • Department of Applied Mathematics, University of Twente, P.O. Box 217, 7500 AE Enschede, Netherlands

  • Venue:
  • Discrete Applied Mathematics - The 1st cologne-twente workshop on graphs and combinatorial optimization (CTW 2001)
  • Year:
  • 2004

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Abstract

A cut [S, S] is a sparsest cut of a graph G if its cut value |S||S|/|[S, S]| is maximum (this is the reciprocal of the well-known edge-density of the cut). In the (undirected) uniform concurrent flow problem on G, between every vertex pair of G flow paths with a total flow of 1 have to be established. The objective is to minimize the maximum amount of flow through an edge (edge congestion). The minimum congestion value of the uniform concurrent flow problem on G is an upper bound for the maximum cut value of cuts in G. If both values are equal, G is called a bottleneck graph. The bottleneck properties of cartesian product graphs G × H are studied. First, a flow in G × H is constructed using optimal flows in G and H, and proven to be optimal. Secondly, two cuts are constructed in G × H using sparsest cuts of G and H. It is shown that one of these cuts is a sparsest cut of G × H. As a consequence, we can prove that G × H is (not) a bottleneck graph if both G and H are (not) bottleneck graphs.