A Graph Reduction Step Preserving Element-Connectivity and Applications

  • Authors:
  • Chandra Chekuri;Nitish Korula

  • Affiliations:
  • Dept. of Computer Science, University of Illinois, Urbana, 61801;Dept. of Computer Science, University of Illinois, Urbana, 61801

  • Venue:
  • ICALP '09 Proceedings of the 36th International Colloquium on Automata, Languages and Programming: Part I
  • Year:
  • 2009

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Abstract

Given an undirected graph G = (V ,E ) and subset of terminals T *** V , the element-connectivity *** *** G (u ,v ) of two terminals u ,v *** T is the maximum number of u -v paths that are pairwise disjoint in both edges and non-terminals V *** T (the paths need not be disjoint in terminals). Element-connectivity is more general than edge-connectivity and less general than vertex-connectivity. Hind and Oellermann [18] gave a graph reduction step that preserves the global element-connectivity of the graph. We show that this step also preserves local connectivity, that is, all the pairwise element-connectivities of the terminals. We give two applications of the step to connectivity and network design problems: First, we show a polylogarithmic approximation for the problem of packing element-disjoint Steiner forests in general graphs, and an O (1)-approximation in planar graphs. Second, we find a very short and intuitive proof of a spider-decomposition theorem of Chuzhoy and Khanna [10] in the context of the single-sink k -vertex-connectivity problem. Our results highlight the effectiveness of the element-connectivity reduction step; we believe it will find more applications in the future.