Improved Approximation Algorithms for PRIZE-COLLECTING STEINER TREE and TSP

  • Authors:
  • Aaron Archer;Mohammad Hossein Bateni;Mohammad Taghi Hajiaghayi;Howard Karloff

  • Affiliations:
  • -;-;-;-

  • Venue:
  • FOCS '09 Proceedings of the 2009 50th Annual IEEE Symposium on Foundations of Computer Science
  • Year:
  • 2009

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Abstract

We study the prize-collecting versions of the Steiner tree, traveling salesman, and stroll (a.k.a. Path-TSP) problems (PCST, PCTSP, and PCS, respectively): given a graph (V, E) with costs on each edge and a penalty (a.k.a. prize) on each node, the goal is to find a tree (for PCST), cycle (for PCTSP), or stroll (for PCS) that minimizes the sum of the edge costs in the tree/cycle/stroll and the penalties of the nodes not spanned by it. In addition to being a useful theoretical tool for helping to solve other optimization problems, PCST has been applied fruitfully by AT&T to the optimization of real-world telecommunications networks. The most recent improvements for the first two problems, giving a 2-approximation algorithm for each, appeared first in 1992. (A 2-approximation for PCS appeared in 2003.) The natural linear programming (LP) relaxation of PCST has an integrality gap of 2, which has been a barrier to further improvements for this problem. We present (2-epsilon)-approximation algorithms for all three problems, connected by a unified technique for improving prize-collecting algorithms that allows us to circumvent the integrality gap barrier.