Matroid and knapsack center problems

  • Authors:
  • Danny Z. Chen;Jian Li;Hongyu Liang;Haitao Wang

  • Affiliations:
  • Department of Computer Science and Engineering, University of Notre Dame, Notre Dame, IN;Institute for Interdisciplinary Information Sciences (IIIS), Tsinghua University, Beijing, China;Institute for Interdisciplinary Information Sciences (IIIS), Tsinghua University, Beijing, China;Department of Computer Science, Utah State University, Logan, UT

  • Venue:
  • IPCO'13 Proceedings of the 16th international conference on Integer Programming and Combinatorial Optimization
  • Year:
  • 2013

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Abstract

In the classic k-center problem, we are given a metric graph, and the objective is to open k nodes as centers such that the maximum distance from any vertex to its closest center is minimized. In this paper, we consider two important generalizations of k-center, the matroid center problem and the knapsack center problem. Both problems are motivated by recent content distribution network applications. Our contributions can be summarized as follows: 1 We consider the matroid center problem in which the centers are required to form an independent set of a given matroid. We show this problem is NP-hard even on a line. We present a 3-approximation algorithm for the problem on general metrics. We also consider the outlier version of the problem where a given number of vertices can be excluded as the outliers from the solution. We present a 7-approximation for the outlier version. 2 We consider the (multi-)knapsack center problem in which the centers are required to satisfy one (or more) knapsack constraint(s). It is known that the knapsack center problem with a single knapsack constraint admits a 3-approximation. However, when there are at least two knapsack constraints, we show this problem is not approximable at all. To complement the hardness result, we present a polynomial time algorithm that gives a 3-approximate solution such that one knapsack constraint is satisfied and the others may be violated by at most a factor of 1+ε. We also obtain a 3-approximation for the outlier version that may violate the knapsack constraint by 1+ε.