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The p-median problem has been widely studied in combinatorial optimisation, but its generalisation to the capacitated case has not. We propose a branch and price algorithm, comparing it with a standard MIP solver and a branch and bound algorithm based on Lagrangean relaxation. We present computational experience, using test instances drawn from the literature and new instances with higher ratio between...
Wireless communication is used in many different situations such as mobile telephony, radio and TV broadcasting, satellite communication, and military operations. In each of these situations a frequency assignment problem arises with application specific characteristics. Researchers have developed different modeling ideas for each of the features of the problem, such as the handling of interference...
This is a summary of the most important results presented in the authors PhD thesis. This thesis, written in English, was defended on 13 June 2003 and supervised by Johan Springael and Gerrit K. Janssens. A copy is available from the author upon request. This PhD thesis focuses on stochastic problems and develops a framework to find robust and flexible solutions of such problems. The framework is...
This paper considers packing problems with balancing conditions and items consisting of clusters of parallelepipeds (mutually orthogonal, i.e. tetris-like items). This issue is quite frequent in space engineering and a real-world application deals with the Automated Transfer Vehicle project (funded by the European Space Agency), at present under development. A Mixed Integer Programming (MIP) approach...
Equal-processing-time scheduling problems whose complexity status has been unknown are shown to be solved in polynomial time by well-known and relatively new techniques. Single-machine, parallel-machine, parallel-batch, open-shop, flow-shop and job-shop environments are touched upon.
The pervasiveness and impact on society and on every day human life of technology has led to a growing awareness that science and technology cannot be considered above or beyond the realm of value judgements and hence of ethics. This is especially true for Operations Research / Management Science (OR/MS), that particular science which is concerned with methodologies for scientifically deciding how...
Webs and antiwebs are natural generalizations of odd holes and odd antiholes with circular symmetry of their maximum cliques and stable sets. Webs and antiwebs turned out to play a crucial role for describing the stable set polytopes for larger graph classes. In this short note we obtain, with the help of a result of Shepherd (1995), a complete description of the stable set polytopes for antiwebs...
Computing a schedule for a single machine problem is often difficult, but when the data are uncertain, the problem is much more complicated. In this paper, we modify a genetic algorithm to compute robust schedules when release dates are subject to small variations. Two types of robustness are distinguished: quality robustness or robustness in the objective function space and solution robustness or...
We survey the main results in the authors PhD Thesis presented in December 2002 at the Universit Libre de Bruxelles and supervised by Prof. Martine Labb. The dissertation is written in English and is available at smg.ulb.ac.be. Several versions of concentrator location problems in telecommunication networks are studied. The thesis presents a list of polyhedral results for these problems and a branch...
We review the recent three-volume monograph authored by Alexander Schrijver, Combinatorial Optimization - Polyhedra and Efficiency, Springer-Verlag, 2003, ISBN 3-540-44389-4, 1881 pages (in a slip-case), price: 89,95 .
. We survey the main results obtained by the author in his PhD dissertation supervised by Prof. Costas Pantelides. It was defended at the Imperial College, London. The thesis is written in English and is available from http://or.elet.polimi.it/people/Liberti/phdtesis.ps.gz . The most widely employed deterministic method for the global solution of nonconvex NLPs and MINLPs is the spatial Branch-and-Bound...
. In Combinatorial Optimization, one is frequently faced with linear programming (LP) problems with exponentially many constraints, which can be solved either using separation or what we call compact optimization. The former technique relies on a separation algorithm, which, given a fractional solution, tries to produce a violated valid inequality. Compact optimization relies on describing the feasible...
. This paper presents upper bounds for the Satellite Revenue Selection and Schedulingproblem (SRSS). A compact model of this generalized Prize Collecting Traveling Salesman Problem with Time Windows is defined and enriched with valid inequalities based on task interval reasoning. The non-concavity of the objective function to be maximized is also studied. Finally a Russian Dolls approach combines...
. This text summarises the PhD thesis that Roel Leus presented to obtain the degree of Doctor in Applied Economics at the Katholieke Universiteit Leuven, in September 2003. The promotor of the thesis was professor Willy Herroelen. The thesis is written in English and is available from the author’s website. The goal of the thesis was to provide recommendations for the detailed scheduling of multi-project...
. This paper is devoted to some selected topics relating Combinatorial Optimization and Hierarchical Classification. It is oriented toward extensions of the standard classification schemes (the hierarchies): pyramids, quasi-hierarchies, circular clustering, rigid clustering and others. Bijection theorems between these models and dissimilarity models allow to state some clustering problems as optimization...
. This is a summary of the most important results presented in the author’s PhD thesis (Spanjaard 2003). This thesis, written in French, was defended on 16 December 2003 and supervised by Patrice Perny. A copy is available from the author upon request. This thesis deals with the search for preferred solutions in combinatorial optimization problems (and more particularly graph problems). It aims at...
. In this paper we address the problem of aggregating outranking statements from multiple preference criteria of ordinal significance. The concept of ordinal concordance of a global outranking situation is defined and an operational test for its presence is developed. Finally, we propose a new kind of robustness analysis for global outranking statements integrating classical dominance, ordinal and...
. We survey the main results of the author’s PhD thesis that was supervised by Claude Le Pape (ILOG, France) and Philippe Michelon (Université d’Avignon, France) and has been defended in June 2004. The dissertation is written in French and is available from the author. It introduces several strategies for integrating local search techniques into mixed integer programming, with an emphasis on generic...
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