Recent contributions of OR to network optimization

This feature issue of the European Journal of Operational Research was originally thought as the follow up of the AIRO Winter Conference 2005 (AW05). The meeting, held in Cortina d’Ampezzo from January 31st to February 5th, 2005, was conceived in its early editions and then enthusiastically supported by the late Mario Lucertini and Stefano Pallottino, whose original contribution to network problems is well known to many scholars of OR, and whom the AW conferences are now devoted to. The issue collects contributions from participants to AW05, as well as other papers that were accurately selected (about 15% of submitted papers) from a large number of manuscripts coming from the global OR community. The outcome is in our opinion a nice multicolour picture of recent advances in network optimization: as such, it includes combinatorial problems and algorithms, game-theoretical models, simulation and queuing theory results, with applications ranging from telecommunication, through political districting, to road traffic management. The first paper of the volume addresses a class of Linear Ordering problems on complete directed graphs. Livio Bertacco, Lorenzo Brunetta and Matteo Fischetti focus on a particular case where the cost of positioning a node is recursively defined through the costs of the nodes and arcs which proceed from it in the order. The problem, referred to as the Linear Ordering Problem with Cumulative Costs, is motivated by applications in wireless telecommunication networks. The paper, besides a clear theoretical characterization including an analysis of computational complexity, provides a set of algorithms to tackle the problem from the practical side, and a large body of experimental results.