NEW REDUCTION TECHNIQUES FOR THE GROUP STEINER TREE PROBLEM.

The group Steiner tree problem consists of, given a graph G, a collection R of subsets of V (G), and a positive cost ce for each edge e of G, finding a minimum-cost tree in G that contains at least one vertex from each R ∈ R. We call the sets in R groups. The well-known Steiner tree problem is the special case of the group Steiner tree problem in which each set in R is unitary. In this paper, we present a general reduction test designed to remove group vertices, that is, vertices belonging to some group. Through the use of these tests we can conclude that a given group vertex can be considered a nonterminal and hence can be removed from its group. We also present some computational results on instances from SteinLib [T. Koch, A. Martin, and S. Voss, SteinLib: An updated library on Steiner tree problems in graphs, in Steiner Trees in Industry, Kluwer Academic Publishers, Dordrecht, The Netherlands, 2001, pp. 285-325]. [ABSTRACT FROM AUTHOR]