Improved approximation algorithm for convex recoloring of trees

  • Authors:
  • Reuven Bar-Yehuda;Ido Feldman;Dror Rawitz

  • Affiliations:
  • Department of Computer Science, Technion, Haifa, Israel;Department of Computer Science, Technion, Haifa, Israel;Caesarea Rothschild Institute, University of Haifa, Haifa, Israel

  • Venue:
  • WAOA'05 Proceedings of the Third international conference on Approximation and Online Algorithms
  • Year:
  • 2005

Quantified Score

Hi-index 0.00

Visualization

Abstract

A pair (T,C) of a tree T and a coloring C is called a colored tree. Given a colored tree (T,C) any coloring C′ of T is called a recoloring of T. Given a weight function on the vertices of the tree the recoloring distance of a recoloring is the total weight of recolored vertices. A coloring of a tree is convex if for any two vertices u and v that are colored by the same color c, every vertex on the path from u to v is also colored by c. In the minimum convex recoloring problem we are given a colored tree and a weight function and our goal is to find a convex recoloring of minimum recoloring distance. The minimum convex recoloring problem naturally arises in the context of phylogenetic trees. Given a set of related species the goal of phylogenetic reconstruction is to construct a tree that would best describe the evolution of this set of species. In this context a convex coloring correspond to perfect phylogeny. Since perfect phylogeny is not always possible the next best thing is to find a tree which is as close to convex as possible, or, in other words, a tree with minimum recoloring distance. We present a (2+ε)-approximation algorithm for the minimum convex recoloring problem, whose running time is O(n2+n(1/ε)2 41/ε). This result improves the previously known 3-approximation algorithm for this NP-hard problem.