A two-stage stochastic transportation problem with fixed handling costs and a priori selection of the distribution channels

In this paper, a transportation problem comprising stochastic demands, fixed handling costs at the origins, and fixed costs associated with the links is addressed. It is assumed that uncertainty is adequately captured via a finite set of scenarios. The problem is formulated as a two-stage stochastic program. The goal is to minimize the total cost associated with the selected links plus the expected transportation and fixed handling costs. A prototype problem is initially presented which is then progressively extended to accommodate capacities at the origins and multiple commodities. The results of an extensive set of computational tests are reported and discussed

The Single Period Coverage Facility Location Problem: Lagrangean heuristic and column generation approaches

In this paper we introduce the Single Period Coverage Facility Location Problem. It is a multi-period discrete location problem in which each customer is serviced in exactly one period of the planning horizon. The locational decisions are made independently for each period, so that the facilities that are open need not be the same in different time periods. It is also assumed that at each period there is a minimum number of customers that can be assigned to the facilities that are open. The decisions to be made include not only the facilities to open at each time period and the time period in which each customer will be served, but also the allocation of customers to open facilities in their service period. We propose two alternative formulations that use different sets of decision variables. We prove that in the first formulation the coefficient matrix of the allocation subproblem that results when fixing the facilities to open at each time period is totally unimodular. On the other hand, we also show that the pricing problem of the second model can be solved by inspection. We prove that a Lagrangean relaxation of the first one yields the same lower bound as the LP relaxation of the second one. While the Lagrangean dual can be solved with a classical subgradient optimization algorithm, the LP relaxation requires the use of column generation, given the large number of variables of the second model. We compare the computational burden for obtaining this lower bound through both models

A computational comparison of several formulations for the multi-period incremental service facility location problem

The Multi-period Incremental Service Facility Location Problem, which was recently introduced, is a strategic problem for timing the location of facilities and the assignment of customers to facilities in a multi-period environment. Aiming at finding the strongest formulation for this problem, in this work we study three alternative formulations based on the so-called impulse variables and step variables. To this end, an extensive computational comparison is performed. As a conclusion, the hybrid impulse–step formulation provides better computational results than any of the other two formulations

Network flow based approaches for the pipelines routing problem in naval design

In this paper we propose a general methodology for the optimal automatic routing of spatial pipelines motivated by a recent collaboration with Ghenova, a leading Naval Engineering company. We provide a minimum cost multicommodity network flow based model for the problem incorporating all the tech- nical requirements for a feasible pipeline routing. A branch-and-cut approach is designed and different matheuristic algorithms are derived for solving efficiently the problem. We report the results of a battery of computational experiments to assess the problem performance as well as a case study of a real-world naval instance provided by our partner company.Ministerio de Ciencia Y Tecnología (MCYT). España PID2020-114594GB-C21European Commission (EC). Fondo Europeo de Desarrollo Regional (FEDER) US-1256951Junta de Andalucía P18-FR-1422Junta de Andalucía CEI-3-FQM331Junta de Andalucía B-FQM-322-UGR2

Algunos problemas en Teoría de Localización

"En esta tesis se abordan diversos problemas dentro de diferentes campos de la teoría de localización. En un primer capítulo se da una introducción histórica a la teoría de la localización así como una clasificación de los diferentes problemas tratados e

Partially ordered cooperative games: extended core and Shapley value

In this paper we analyze cooperative games whose characteristic function takes values in a partially ordered linear space. Thus, the classical solution concepts in cooperative game theory have to be revisited and redefined: the core concept, Shapley–Bondareva theorem and the Shapley value are extended for this class of games. The classes of standard, vector-valued and stochastic cooperative games among others are particular cases of this general theory

Dynamically second-preferred p-center problem

This paper deals with the Dynamically Second-preferred p-center Problem (DSpP). In this problem, cus- tomers’ preferences and subsets of sites that each customer is willing to accept as service centers are taken into account. It is assumed that centers can fail and, thus, the decision maker is risk-averse and makes his decision taking into account not only the most favourite centers of the customers but also the worst case situation whenever they evaluate their preferred second opportunity. Specifically, the new problem aims at choosing at most pcenters so that each demand point can visit at least two acceptable centers and the maximum sum of distances from any demand point to any of its preferred centers plus the distance from any of the preferred centers to any of the centers the user prefers once he is there is minimized. The problem is NP-hard as an extension of the p-next center problem. The paper presents three different mixed-integer linear programming formulations that are valid for the problem. Each for- mulation uses different space of variables giving rise to some strengthening using valid inequalities and variable fixing criteria that can be applied when valid upper bounds are available. Exact methods are limited so that a heuristic algorithm is also developed to provide good quality solution for large size in- stances. Finally, an extensive computational experience has been performed to assess the usefulness of the formulations to solve DSpP using standard MIP solvers.Ministerio de Ciencia e Innovación (MICIN). España PID 2020-114594GB-C21Junta de Andalucía FEDER-US-1256951Junta de Andalucía CEI-3-FQM331Junta de Andalucía P18-FR-142