Multiple neighborhoods in tabu search: successful applications for operations management problems

A metaheuristic is a refined solution method able to find a satisfying solution to a difficult problem in a reasonable amount of time. A local search metaheuristic works on a single solution and tries to improve it iteratively. Tabu search is one of the most famous local search, where at each iteration, a neighbor solution is generated from the current solution by performing a specific modification (called a move) on the latter. In contrast with most of the existing literature, the goal of this paper is to present tabu search approaches where different neighborhood structures (i.e., different types of moves) are jointly used. The discussion is illustrated for various operations management problems: truck loading, job scheduling, inventory management, and dimensioning of assembly lines

A solution method for a car fleet management problem with maintenance constraints

The problem retained for the ROADEF'99 international challenge was an inventory management problem for a car rental company. It consists in managing a given fleet of cars in order to satisfy requests from customers asking for some type of cars for a given time period. When requests exceed the stock of available cars, the company can either offer better cars than those requested, subcontract some requests to other providers, or buy new cars to enlarge the available stock. Moreover, the cars have to go through a maintenance process at a regular basis, and there is a limited number of workers that are available to perform these maintenances. The problem of satisfying all customer requests at minimum cost is known to be NP-hard. We propose a solution technique that combines two tabu search procedures with algorithms for the shortest path, the graph coloring and the maximum weighted independent set problems. Tests on benchmark instances used for the ROADEF'99 challenge give evidence that the proposed algorithm outperforms all other existing methods (thirteen competitors took part to this contest

Heuristics for a project management problem withincompatibility and assignment costs

Consider a project which consists of a set of jobs to be performed, assuming each job has a duration of at most one time period. We assume that the project manager provides a set of possible durations (in time periods) for the whole project. When a job is assigned to a specific time period, an assignment cost is encountered. In addition, for some pairs of jobs, an incompatibility cost is encountered if they are performed at the same time period. Both types of cost depend on the duration of the whole project, which also has to be determined. The goal is to assign a time period to each job while minimizing the costs. We propose a tabu search heuristic, as well as an adaptive memory algorithm, and compare them with other heuristics on large instances, and with an exact method on small instances. Variations of the problems are also discusse

Les Lumières de Hong Kong et les brumes de la traduction

Depuis quelques années, un grand nombre d'oeuvres littéraires chinoises contemporaines, principalement des romans, ont été traduites en français ; certains éditeurs (Picquier, Actes Sud, Bleu de Chine, les éditions de l’Aube, Gallimard-Folio, etc.) se montrent très actifs dans ce domaine, ce qui bien sûr est une bonne chose. Les traductions publiées par leurs soins permettent à un lectorat non sinisant de se faire au moins une idée de la richesse de la création littéraire contemporaine en Chi..

Graph colouring approaches for a satellite range scheduling problem

A goal of this paper is to efficiently adapt the best ingredients of the graph colouring techniques to an NP-hard satellite range scheduling problem, called MuRRSP. We propose two new heuristics for the MuRRSP, where as many jobs as possible have to be scheduled on several resources, while respecting time and capacity constraints. In the permutation solution space, which is widely used by other researchers, a solution is represented by a permutation of the jobs, and a schedule builder is needed to generate and evaluate a feasible schedule from the permutation. On the contrary, our heuristics are based on the solution space which contains all the feasible schedules. Based on the similarities between the graph colouring problem and the MuRRSP, we show that the latter solution space has significant advantages. A tabu search and an adaptive memory algorithms are designed to tackle the MuRRSP. These heuristics are derived from efficient graph colouring methods. Numerical experiments, performed on large, realistic, and challenging instances, showed that our heuristics are very competitive, robust, and outperform algorithms based on the permutation solution spac

Les Lumières de Hong Kong and the mist of translation

Over the past few years, a large number of works of contemporary Chinese literature, primarily novels, have been translated into French, and several publishers (Picquier, Actes Sud, Bleu de Chine, les éditions de l’Aube, Gallimard-Folio, etc.) are proving to be very active in this domain. This is certainly a good thing. The translations that they have published allow a readership previously unfamiliar with China and its literature to gain at least some idea of the richness of contemporary cre..

Les Lumières de Hong Kong et les brumes de la traduction

Depuis quelques années, un grand nombre d'oeuvres littéraires chinoises contemporaines, principalement des romans, ont été traduites en français ; certains éditeurs (Picquier, Actes Sud, Bleu de Chine, les éditions de l’Aube, Gallimard-Folio, etc.) se montrent très actifs dans ce domaine, ce qui bien sûr est une bonne chose. Les traductions publiées par leurs soins permettent à un lectorat non sinisant de se faire au moins une idée de la richesse de la création littéraire contemporaine en Chi..

Solution Methods for a Scheduling Problem with Incompatibility and Precedence Constraints

Consider a project which consists in a set of operations to be performed, assuming the processing time of each operation is at most one time period. In this project, precedence and incompatibility constraints between operations have to be satisfied. The goal is to assign a time period to each operation while minimizing the duration of the whole project and while taking into account all the constraints. Based on the mixed graph coloring model and on an efficient and quick tabu search algorithm for the usual graph coloring problem, we propose a tabu search algorithm as well as a variable neighborhood search heuristic for the considered scheduling problem. We formulate an integer linear program (useful for the CPLEX solver) as well as a greedy procedure for comparison considerations. Numerical results are reported on instances with up to 500 operations

Multi-coloring and job-scheduling with assignment and incompatibility costs

Consider a scheduling problem (P) which consists of a set of jobs to be performed within a limited number of time periods. For each job, we know its duration as an integer number of time periods, and preemptions are allowed. The goal is to assign the required number of time periods to each job while minimizing the assignment and incompatibility costs. When a job is performed within a time period, an assignment cost is encountered, which depends on the involved job and on the considered time period. In addition, for some pairs of jobs, incompatibility costs are encountered if they are performed within common time periods. (P) can be seen as an extension of the multi-coloring problem. We propose various solution methods for (P) (namely a greedy algorithm, a descent method, a tabu search and a genetic local search), as well as an exact approach. All these methods are compared on different types of instance