Two O (log* k)-Approximation Algorithms for the Asymmetric k-Center Problem

  • Authors:
  • Aaron Archer

  • Affiliations:
  • -

  • Venue:
  • Proceedings of the 8th International IPCO Conference on Integer Programming and Combinatorial Optimization
  • Year:
  • 2001

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Abstract

Given a set V of n points and the distances between each pair, the k-center problem asks us to choose a subset C ⊆ V of size k that minimizes the maximum over all points of the distance from C to the point. This problem is NP-hardev en when the distances are symmetric and satisfy the triangle inequality, and Hochbaum and Shmoys gave a best-possible 2-approximation for this case. We consider the version where the distances are asymmetric. Panigrahy and Vish wanathan gave an O(log* n)-approximation for this case, leading many to believe that a constant approximation factor shouldb e possible. Their approach is purely combinatorial. We show how to use a natural linear programming relaxation to define a promising new measure of progress, anduse it to obtain two different O(log*k)-approximation algorithms. There is hope of obtaining further improvement from this LP, since we do not know of an instance where it has an integrality gap worse than 3.