Showing papers by "David Pisinger published in 2009"

Two- and Three-index formulations of the Minimum Cost Multicommodity k-splittable Flow Problem

Abstract: The multicommodity flow problem (MCFP) considers the efficient routing of commodities from their origins to their destinations subject to capacity restrictions and edge costs. Baier et al. [G. Baier, E. Kohler, M. Skutella, On the k-splittable flow problem, in: 10th Annual European Symposium on Algorithms, 2002, 101–113] introduced the maximum flow multicommodity k-splittable flow problem (MCkFP) where each commodity may use at most k paths between its origin and its destination. This paper studies the NP -hard minimum cost multicommodity k-splittable flow problem (MCMCkFP) in which a given flow of commodities has to be satisfied at the lowest possible cost. The problem has applications in transportation problems where a number of commodities must be routed, using a limited number of distinct transportation units for each commodity. Based on a three-index formulation by Truffot et al. [J. Truffot, C. Duhamel, P. Mahey, Branch and price pour le probleme du multiflot k-separable de cout minimal, in: LIMOS, UMR 6158 – CNRS, ROADEF’05, 2005] we present a new two-index formulation for the problem, and solve both formulations through branch-and-price. The three-index algorithm by Truffot et al. is improved by introducing a simple heuristic method to reach a feasible solution by eliminating some symmetry. A novel branching strategy for the two-index formulation is presented, forbidding subpaths in the branching children. Though the proposed heuristic for the three-index algorithm improves its performance, the three-index algorithm is still outperformed by the two-index algorithm, both with respect to running time and to the number of solved test instances.

Integration of loading and routing in logistics outsourcing

Abstract: Transportation management is a crucial issue in today’s business environment. Firms pay attention to their core business and focus their competences and resources to improve and strengthen their competitive advantages. Consequently, firms find themselves integrated in a network of agents, since they purchase products and services to complete their processes. Logistics activities and services are committed to specialized companies. This changes the standard formulations of delivery and routing problems. This paper focuses the attention in a new formulation of the transportation problem accounting the supplier relationships of freight and groupage and the transportation problem. Transportation Management includes load planning and delivery route planning, respectively referred as Container Loading Problem and Vehicle Routing Problem. The two problems are very investigated but deal with optimization separately. This paper focuses the attention on an integrated approach considering also the outsourcing of logistic.