1,113 research outputs found
The dispatching problem on multitrack territories: Heuristic approaches based on mixed integer linear programming
No full textTrains running through railway lines often accumulate some delay. When this happens, rescheduling and rerouting decisions must be quickly taken in real time. Despite the fact that even a single wrong decision may deteriorate the performance of the whole railway network, this complex optimization task is still basically performed by human operators. In very recent years, the interest of train operators to implement automated decision systems has grown. Not incidentally, the railway application section (RAS) of INFORMS has issued a challenge devoted to this problem concomitantly with the INFORMS Annual Meeting 2012. In this article, we describe two heuristic approaches to solve the RAS problem based on a mixed integer linear programming formulation, and we report computational results on the three RAS instances and on an additional set of instances defined on a more congested network. Computational results on the challenge test bed show that our algorithms positively compare with other approaches to the RAS problem
A computational study of exact knapsack separation for the generalized assignment problem
No full textGeneralized assignment problem, Cutting plane algorithm, Exact separation,
Single-item reformulations for a vendor managed inventory routing problem: Computational experience with benchmark instances
No full textSolving the dispatching problem on multi-track territories by mixed integer linear programming
No full textComputational testing of a separation procedure for the knapsack set with a single continuous variable
No full text We study an exact separation procedure—SEP-MK—for the knapsack set with a single continuous variable XMK. Then, we address the question of whether SEP-MK can be of practical use in tightening mixed-integer programming (MIP) formulations when using standard (floating-point) MIP solvers. To this purpose, we present a separation procedure for MIP problems—SEP-MIPMK—where we derive knapsack sets of the form XMK by aggregating the continuous variables in the mixed knapsack inequalities of the formulation. Then, we use SEP-MK to generate cutting planes. Before the continuous variables are aggregated, the mixed knapsack inequalities are modified through the use of a bound substitution procedure to take into account fixed and variable bounds on the continuous variables. Bound substitution is made according to some heuristic rules, so even if its basic component SEP-MK is “exact,” the overall separation procedure for MIP problems, SEP-MIPMK, is heuristic. We perform a computational study on a wide set of mixed-integer programming instances from the MIPLIB 2003 [Achterberg, T., T. Koch, A. Martin. 2006. Mixed Integer Problem Library (MIPLIB) 2003. Konrad-Zuse-Zentrum für Informationstechnik Berlin, Berlin. http://miplib.zib.de] and Mittelmann [Mittelmann, H. 2010. MILP testcases. http://plato.asu.edu/ftp/milp] benchmark sets. Computational experiments confirm that lifted cover and mixed-integer rounding (MIR) inequalities are effective from a computational viewpoint. Nevertheless, there are several instances where SEP-MIPMK is able to significantly raise the lower bounds given by lifted cover and MIR inequalities. </jats:p
A computational study of dicut reformulation for the Single Source Capacitated Facility Location problem
No full textThe Capacitated Facility Location Problem is to locate a set of facilities with capacity constraints, with the aim of satisfying at the minimum cost the demands of a set of clients. The Single Source version (SingleCFLP) of the problem has the additional requirement that each client must be assigned to a single facility.
In this paper a reformulation of the problem based on Dicut Inequalities is proposed. Based on the observation that Dicut Inequalities are that are knapsack inequalities, an exact knapsack
separation procedure is used to derive cutting planes from the inequalities which are valid for the Dicut Polytope.
The separation procedure for Dicut inequalities has been embedded into a Branch-and-Cut framework and a computational experience is reported on a wide set of benchmark instances
An optimization approach for congestion control in network routing with quality of service requirements
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