Variable Neighborhood Search (VNS) is a recent and effective metaheuristic for solving combinatorial and global optimization problems. It is capable of escaping from the local optima by systematic changes of the neighborhood structures within the search. In this paper several parallelization strategies for VNS have been proposed and compared on the large instances of the p-median problem. ∗The ...

In this paper we deal with the problem of building new or extending an existing railway infrastructure. The goal is to determine a minimum cost infrastructure fulfilling the requirements defined by an integrated timetable and the operation of the railway system. We first model this planning task as a combinatorial network optimization problem, capturing the essential aspects. We then present a ...

We introduce a real-life problem faced by the blood bank of the Austrian Red Cross for Eastern Austria: how to cost-effectively organize the periodic delivery of blood products to Austrian hospitals. We present various solution approaches, based on integer programming and variable neighborhood search, and empirically evaluate their performance. Moreover, we study the potential value of switchin...

Public bike sharing systems are important alternatives to motorized individual traffic and are gaining popularity in larger cities worldwide. In order to maintain user satisfaction, operators need to actively rebalance the systems so that there are enough bikes available for rental as well as sufficient free slots for returning them at each station. This is done by a vehicle fleet that moves bi...

We present two heuristic methods for solving the Discrete Ordered Median Problem (DOMP), for which no such approaches have been developed so far. The DOMP generalizes classical discrete facility location problems, such as the p-median, p-center and Uncapacitated Facility Location problems. The first procedure proposed in this paper is based on a genetic algorithm developed by Moreno Vega [MV96]...