LIPIcs.ISAAC.2024.7.pdf
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In this paper, we consider the study for the connected minimum sum of radii problem. In this problem, we are given as input a metric defined on a set of facilities and clients, along with some cost parameters. The objective is to open a subset of facilities, assign every client to an open facilitiy, and connect open facilities using a Steiner tree so that the weighted (by cost parameters) sum of the maximum assignment distance of each facility and the Steiner tree cost is minimized. This problem introduces the min-sum radii objective, an objective function that is widely considered in the clustering literature, to the connected facility location problem, a well-studied network design/clustering problem. This problem is useful in communication network design on a shared medium, or energy optimization of mobile wireless chargers. We present both a constant-factor approximation algorithm and hardness results for this problem. Our algorithm is based on rounding an LP relaxation that jointly models the min-sum of radii problem and the rooted Steiner tree problem. To round the solution we use a careful clustering procedure that guarantees that every open facility has a proxy client nearby. This allows a reinterpretation for part of the LP solution as a fractional rooted Steiner tree. Combined with a cost filtering technique, this yields a 5.542-approximation algorithm.
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