Navegando por Autor "Contreras, Ivan"

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    A comparison of separation routines for benders optimality cuts for two-level facility location problems.
    (2020) Oliveira, Paganini Barcellos de; Contreras, Ivan; Camargo, Ricardo Saraiva de; Miranda Junior, Gilberto de
    This paper studies two-level uncapacitated facility location problems, a class of discrete location problems that consider different hierarchies of facilities and their interactions. Benders reformulations for both single and multiple assignment variants and while several separation procedures for three classes of Benders cuts are presented: standard optimality cuts, lifted optimality cuts, and non-dominated optimality cuts. Extensive computational experiments are performed on difficult and large-scale benchmark instances to assess the performance of the considered separation routines.
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    Multimodal hub network design with flexible routes.
    (2021) Real, Luiza Bernardes; Contreras, Ivan; Cordeau, Jean François; Camargo, Ricardo Saraiva de; Miranda Junior, Gilberto de
    This paper introduces a multimodal hub network design problem with flexible routes. Routes are flexible in the sense that they may contain a mix of hub and non-hub nodes. Nonetheless, commodity transfers can only occur at hubs, while transportation costs are flow-dependent, i.e., scale economies stem from the transport technology chosen to operate the routes. We propose a mixed integer mathematical program, and two metaheuristics based on the adaptive large neighborhood search paradigm to solve the problem. Extensive computational experiments show the performance of the formulation and of the devised algorithms in solving benchmark instances with up to 50 nodes.