Managing a Time Expanded Network through Project-and-Lift
Résumé
Vehicle
Routing Problems with synchronizations or resource transfers. However, such models are usually difficult to handle due to their large size and because the reduction techniques to discard some arcs and vertices may introduce errors with an unpredictable impact on feasibility and on solution quality. Recently, we have developed an alternative two-step approach, that we call “Project-and-lift”, to solve a Relocation Problem using a Mixed Integer Linear Programming Model which involves two coupled flows over a Time Expanded Network. In the first step, we solve a “Projected” version of the problem that handles a part of the time constraints in an implicit way. Then, in the second step we try to convert (i.e., “Lift”) the “projected” solutions into solutions of the Relocation Problem. Here, we slightly improve the objective function of the Projected
model and propose an exact mixed integer linear programming model for the weak version of the Lift problem. We also revisit some of the heuristics that we have proposed to handle this last Lift problem and perform some numerical experiments.