Locating facilities on a network to minimize their average service radius

  • Authors:
  • Davide Bilò;Jörg Derungs;Luciano Gualà;Guido Proietti;Peter Widmayer

  • Affiliations:
  • Institut für Theoretische Informatik, ETH, Zürich, Switzerland;Institut für Theoretische Informatik, ETH, Zürich, Switzerland;Dipartimento di Matematica, Università di Tor Vergata, Roma, Italy;Dipartimento di Informatica, Università di L'Aquila, L'Aquila, Italy and Istituto di Analisi dei Sistemi ed Informatica, CNR, Roma, Italy;Institut für Theoretische Informatik, ETH, Zürich, Switzerland

  • Venue:
  • ISAAC'07 Proceedings of the 18th international conference on Algorithms and computation
  • Year:
  • 2007

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Abstract

Let G = (V,E) denote an undirected weighted graph of n nodes and m edges, and let U ⊆ V. The relative eccentricity of a node v ∈ U is the maximum distance in G between v and any other node of U, while the radius of U in G is the minimum relative eccentricity of all the nodes in U. Several facility location problems ask for partitioning the nodes of G so as to minimize some global optimization function of the radii of the subsets of the partition. Here, we focus on the problem of partitioning the nodes of G into exactly p ≥ 2 non-empty subsets, so as to minimize the sum of the subset radii, called the total radius of the partition. This problem can be easily seen to be NP-hard when p is part of the input, but when p is fixed it can be solved in polynomial time by reducing it to a similar partitioning problem. In this paper, we first present an efficient O(n3) time algorithm for the notable case p = 2, which improves the O(mn2 + n3 log n) running time obtainable by applying the aforementioned reduction. Then, in an effort of characterizing meaningful polynomial-time solvable instances of the problem when p is part of the input, we show that (i) when G is a tree, then the problem can be solved in O(n3p3) time, and (ii) when G has bounded treewidth h, then the problem can be solved in O(n4h+4p3) time.