Benedito, E.; Corominas, A.; Martinez, M.; Mas-Machuca, M. Journal of the Operational Research Society Vol. 67, num. 7, p. 970-981 DOI: 10.1057/jors.2015.110 Data de publicació: 2016-07 Article en revista
This paper deals with strategic capacity planning of a single-site manufacturing system. We propose a MILP model that includes relevant business aspects and possibilities, some of which are only partially or not at all found in the literature. Specifically, we consider decisions on expansion, reduction and renewal of production capacity, and acquisition of storage capacity. In addition, we model aspects such as (a) maintenance costs and unit variable costs depending, respectively, on age and characteristics of facilities, (b) seasonality of the demand and (c) cash flow management, including taxes and, therefore, depreciation of assets. The model maximises the after-tax cash balance at the end of the planning horizon. We also present a computational experiment with 54 instances to show that the model can be solved for a wide range of sizes in a reasonable computing time using comercial software.
Pastor, Rafael; García-Villoria, A.; Laguna, M.; Martí, R. Journal of the Operational Research Society Vol. 66, num. 11, p. 1815-1825 DOI: 10.1057/jors.2014.138 Data de publicació: 2015-11-01 Article en revista
The goal of this work is to develop an improved procedure for the solution of the lexicographic bottleneck variant of the assembly line balancing problem (LB-ALBP). The objective of the LB-ALBP is to minimize the workload of the most heavily loaded workstation, followed by the workload of the second most heavily loaded workstation and so on. This problem-recently introduced to the literature (Pastor, 2011)-has practical relevance to manufacturing facilities. We design, implement and fine-tune GRASP, tabu search (TS) and scatter search (SS) heuristics for the LB-ALBP and show that our procedures are able to obtain solutions of a quality that outperforms previous approaches. We rely on both semi-greedy and memory-based designs that our experiments show to be effective. Experimental results verify the advantages of embedding such designs to improve the solution existing in the literature of this complex problem. Additionally, the extensive experimentation with 48 variants of GRASP, 12 of TS and 1 of SS establishes the benefits of adding enhanced search strategies to basic procedures.
Let us consider that somebody is extremely interested in increasing the probability of a proposal to be approved by a certain committee and that to achieve this goal he/she is prepared to pay off one member of the committee. In a situation like this one, and assuming that vote-buying is allowed and free of stigma, which voter should be offered a bribe? The potential decisiveness index for simple games, which measures the effect that ensuring one positive vote produces for the probability of passing the issue at hand, is a good tool with which to acquire the answer. An axiomatic characterization of this index is given in this paper, and its relation to other classical power indices is shown.
This is a post-peer-review, pre-copyedit version of an article published in Journal of the Operational Research Society. The definitive publisher-authenticated version Freixas, J.; Pons, M. An axiomatic characterization of the potential decisiveness index. Journal of the Operational Research Society, 2015, vol. 66, no. 3, p. 353-359 is available online at: http://www.palgrave-journals.com/jors/journal/v66/n3/full/jors20145a.html
The Response Time Variability Problem (RTVP) is an NP-hard combinatorial scheduling problem, which has recently been reported and formalised in the literature. This problem has a wide range of real-world applications in mixed-model assembly lines, multi-threaded computer systems, broadcast of commercial videotapes and others. The RTVP arises whenever products, clients or jobs need to be sequenced in such a way that the variability in the time between the points at which they receive the necessary resources is minimised. We propose a greedy but adaptive heuristic that avoids being trapped into a poor solution by incorporating a look ahead strategy suitable for this particular scheduling problem. The proposed heuristic outperforms the best existing methods, while being much faster and easier to understand and to implement.
Juan, A.; Faulín, F.; Jorba, J.; Riera, D.; Masip, D.; Barrios, B. Journal of the Operational Research Society Vol. 62, num. 6, p. 1085-1097 DOI: 10.1057/jors.2010.29 Data de publicació: 2011 Article en revista
This paper presents the SR-GCWS-CS probabilistic algorithm that combines Monte Carlo simulation with
splitting techniques and the Clarke and Wright savings heuristic to find competitive quasi-optimal solutions to
the Capacitated Vehicle Routing Problem (CVRP) in reasonable response times. The algorithm, which does
not require complex fine-tuning processes, can be used as an alternative to other metaheuristics—such as
Simulated Annealing, Tabu Search, Genetic Algorithms, Ant Colony Optimization or GRASP, which might be
more difficult to implement and which might require non-trivial fine-tuning processes—when solving CVRP
instances. As discussed in the paper, the probabilistic approach presented here aims to provide a relatively
simple and yet flexible algorithm which benefits from: (a) the use of the geometric distribution to guide the
random search process, and (b) efficient cache and splitting techniques that contribute to significantly reduce
computational times. The algorithm is validated through a set of CVRP standard benchmarks and competitive
results are obtained in all tested cases. Future work regarding the use of parallel programming to efficiently
solve large-scale CVRP instances is discussed. Finally, it is important to notice that some of the principles
of the approach presented here might serve as a base to develop similar algorithms for other routing and
scheduling combinatorial problems.
A variable neighbourhood search algorithm that employs new neighbourhoods is proposed for solving a task allocation problem whose main characteristics are: (i) each task requires a certain amount of resources and each processor has a capacity constraint which limits the total resource of the tasks that are assigned to it; (ii) the cost of solution includes fixed costs when using processors, task assignment costs, and communication costs between tasks assigned to different processors. A computational study shows that the algorithm performs well in terms of time and solution quality relative to other local search procedures that have been proposed.
Annualising working hours (AH) is a means to achieve flexibility in the use of human resources in order to face the seasonal nature of the demand. MILP models are proposed to solve the problem of planning the staff's working hours with an annual horizon. The computational experience with the models leads to the conclusion that MILP is an appropriate way to deal with the problem in many real cases.
This note establishes a connection between two problems that appear in different contexts: the Product Rate Variation (PRV) problem (sequencing units in a mixed-model assembly line in order to maximize the regularity of the sequence with regard to the output of units) and the apportionment problem. This allows us to apply to the PRV problem the properties of the apportionment problem and known procedures for solving it, and suggests alternative approaches to the former problem.