Optimal 3-Terminal Cuts and Linear Programming

  • Authors:
  • William H. Cunningham;Lawrence Tang

  • Affiliations:
  • -;-

  • Venue:
  • Proceedings of the 7th International IPCO Conference on Integer Programming and Combinatorial Optimization
  • Year:
  • 1999

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Abstract

Given an undirected graph G = (V,E) and three specified terminal nodes t1, t2, t3, a 3-cut is a subset A of E such that no two terminals are in the same component of G\A. If a non-negative edge weight ce is specified for each e ∈ E, the optimal 3-cut problem is to find a 3-cut of minimum total weight. This problem is NP-hard, and in fact, is max-SNP-hard. An approximation algorithm having performance guarantee 7/6 has recently been given by Călinescu, Karloff, and Rabani. It is based on a certain linear programming relaxation, for which it is shown that the optimal 3-cut has weight at most 7/6 times the optimal LP value. It is proved here that 7/6 can be improved to 12/11, and that this is best possible. As a consequence, we obtain an approximation algorithm for the optimal 3-cut problem having performance guarantee 12/11.