k-edge-connectivity: approximation and LP relaxation

  • Authors:
  • David Pritchard

  • Affiliations:
  • École Polytechnique Fédérale de Lausanne

  • Venue:
  • WAOA'10 Proceedings of the 8th international conference on Approximation and online algorithms
  • Year:
  • 2010

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Abstract

In the k-edge-connected spanning subgraph problem we are given a graph (V, E) and costs for each edge, and want to find a minimum-cost F ⊂ E such that (V, F) is k-edge-connected. We show there is a constant ε 0 so that for all k 1, finding a (1 + ε)-approximation for k-ECSS is NP-hard, establishing a gap between the unit-cost and general-cost versions. Next, we consider the multi-subgraph cousin of k-ECSS, in which we purchase a multi-subset F of E, with unlimited parallel copies available at the same cost as the original edge. We conjecture that a (1+ Θ(1/k))-approximation algorithm exists, and we describe an approach based on graph decompositions applied to its natural linear programming (LP) relaxation. The LP is essentially equivalent to the Held-Karp LP for TSP and the undirected LP for Steiner tree. We give a family of extreme points for the LP which are more complex than those previously known.