Hans-Christoph Wirth

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We examine a network design problem under the reload cost model. Given an undirected edge colored graph, reload costs on a path arise at a node where the path uses consecutive edges of di(erent colors. We consider the problem of 0nding a spanning tree of minimum diameter with respect to the reload costs. We present lower bounds for the approximability even(More)
We study budget constrained network upgrading problems. We are given an undirected edge weighted graph G V E where node v V can be upgraded at a cost of c v . This upgrade reduces the weight of each edge incident on v. The goal is to find a minimum cost set of nodes to be upgraded so that the resulting network has a minimum spanning tree of weight no more(More)
An instance of the (r, p)-centroid problem is given by an edge and node weighted graph. Two competitors, the leader and the follower, are allowed to place p or r facilities, respectively, into the graph. Users at the nodes connect to the closest facility. A solution of the (r, p)-centroid problem is a leader placement such that the maximum total weight of(More)
An instance of the maximum coverage problem is given by a set of weighted ground elements and a cost weighted family of subsets of the ground element set. The goal is to select a subfamily of total cost of at most that of a given budget maximizing the weight of the covered elements. We formulate the problem on graphs: In this situation the set of ground(More)