The sequential ordering problem (SOP) is the generalisation of the asymmetric travelling salesman problem in which there are precedence relations between pairs of nodes. Hernández & Salazar introduced a multi-commodity flow (MCF) formulation for a generalisation of the SOP in which the vehicle has a limited capacity. We strengthen this MCF formulation by fixing variables and adding valid equati...

We solve an important problem for the liner shipping industry called the Liner Shipping Fleet Repositioning Problem (LSFRP). The LSFRP poses a large financial burden on liner shipping firms. During repositioning, vessels are moved between services in a liner shipping network. Shippers wish to reposition vessels as cheaply as possible without disrupting the cargo flows of the network. The LSFRP ...

This paper presents an algorithm to obtain near optimal solutions for the Steiner tree problem in graphs. It is based on a Lagrangian relaxation of a multi-commodity flow formulation of the problem. An extension of the subgradient algorithm, the volume algorithm, has been used to obtain lower bounds and to estimate primal solutions. It was possible to solve several difficult instances from the ...

We present a generic mathematical modeling approach for solving rolling stock scheduling problems. Our approach is based on a time-space network and a multi-commodity flow model; in order to deal with the various types of rolling stock scheduling problems faced by SNCF planners, it integrates numerous modeling settings and features including maintenance routing requirements which are treated by...

We present results from an experiment where the effects of automatic flow control at a single substation is compared to automatic cooperative concurrent flow control at multiple substations. The latter approach is made possible by equipping individual substations with some computing power and integrating them into a communications network. Software agents, whose purpose is to cooperate with oth...

The availability of commodity multi-core andmulti-processor machinesandthe inherentparallelism inconstraintprogrammingsearchoffer significant opportunities for constraint programming.They also present a fundamental challenge: how to exploit parallelism transparently to speed upconstraintprograms.Thispaper showshowtoparallelize constraintprograms transparently without changes to the code. The ma...

We study the community structure of the multi-network of commodity-specific trade relations among world countries over the 1992-2003 period. We compare structures across commodities and time by means of the normalized mutual information index (NMI). We also compare them with exogenous community structures induced by geographical distances and regional trade agreements. We find that commodityspe...

According to several studies, telecom operators account for a not negligible power consumption, and several initiatives are being put into place to reduce the power consumption of the ICT sector in general. To this goal, we propose a novel approach to switch off some portions of the UMTS core network while still guaranteeing full connectivity and maximum link utilization. After showing that the...

Collaborative filtering is an effective recommendation approach in which the preference of a user on an item is predicted based on the preferences of other users with similar interests. A big challenge in using collaborative filtering methods is the data sparsity problem which often arises because each user typically only rates very few items and hence the rating matrix is extremely sparse. In ...