In this paper we consider the covering problem on a network G = (V, E) with edge demands. The task is to cover a subset J ⊆ E of the edges with a minimum number of facilities within a predefined coverage radius. We focus on both the nodal and the absolute version of this problem. In the latter, facilities may be placed everywhere in the network. While there already exist polynomial time algorithms to solve the problem on trees, we establish a finite dominating set (i.e., a finite subset of points provably containing an optimal solution) for the absolute version in general graphs. Complexity and approximability results are given and a greedy strategy is proved to be a (1 + ln(|J|))‐approximate algorithm. Finally, the different approaches are compared in a computational study.

We investigate the single-source-single-destination "shortest" paths problem in acyclic graphs with ordinal weighted arc costs. We define the concepts of ordinal dominance and efficiency for paths and their associated ordinal levels, respectively. Further, we show that the number of ordinally non-dominated paths vectors from the source node to every other node in the graph is polynomially bounded and we propose a polynomial time labeling algorithm for solving the problem of finding the set of ordinally non-dominated paths vectors from source to sink.

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This article investigates a network interdiction problem on a tree network: given a subset of nodes chosen as facilities, an interdictor may dissect the network by removing a size-constrained set of edges, striving to worsen the established facilities best possible. Here, we consider a reachability objective function, which is closely related to the covering objective function: the interdictor aims to minimize the number of customers that are still connected to any facility after interdiction. For the covering objective on general graphs, this problem is known to be NP-complete (Fröhlich and Ruzika In: On the hardness of covering-interdiction problems. Theor. Comput. Sci., 2021). In contrast to this, we propose a polynomial-time solution algorithm to solve the problem on trees. The algorithm is based on dynamic programming and reveals the relation of this location-interdiction problem to knapsack-type problems. However, the input data for the dynamic program must be elaborately generated and relies on the theoretical results presented in this article. As a result, trees are the first known graph class that admits a polynomial-time algorithm for edge interdiction problems in the context of facility location planning.