References of "Schyns, Michael"
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See detailThree dimensional Bin Packing Problem applied to air transport
Paquay, Célia ULg; Schyns, Michael ULg; Limbourg, Sabine ULg

Conference (2012, February 02)

Packing boxes into containers is a daily process in many di erent elds and especially in transport. However, the particular case of air transport brings some new constraints such as the stability or the ... [more ▼]

Packing boxes into containers is a daily process in many di erent elds and especially in transport. However, the particular case of air transport brings some new constraints such as the stability or the fragility of the cargo. The distribution of the weight has also to be considered. Moreover, this special case also brings some data such as the dimensions of the possible containers, called Unit Load Devices. This paper is concerned with the formulation of the three dimensional palletization which includes the main constraints met in the air cargo industry. It proposes a integer linear program for this combinatorial optimization problem. [less ▲]

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See detailAn Integer Programming model for air transport of hazardous and special shipments
Kleyntssens, Thomas ULg; Limbourg, Sabine ULg; Schyns, Michael ULg

Conference (2012, February 02)

The aircraft loading problem is a real-world combinatorial optimisation problem highly constrained. This weight must be distributed to keep the centre of gravity within speci ed limits. Moreover, an ... [more ▼]

The aircraft loading problem is a real-world combinatorial optimisation problem highly constrained. This weight must be distributed to keep the centre of gravity within speci ed limits. Moreover, an aircraft has usually several cargo compart- ments with speci c contours and structural limitations such as oor loading, com- bined load limits and cumulative load limitations. Finally, some shipments are par- ticularly restrictive to transport, like dangerous goods, live animals and perishable goods. This paper is concerned with the incorporation of these latter constraints in a mixed integer linear program for the problem of loading a set of Unit Load- ing Devices and bulk into an aircraft. Experimental results show that our method achieves optimal solutions within only few seconds. [less ▲]

Detailed reference viewed: 94 (31 ULg)
See detailHow to optimally load a set of containers into an aircraft
Schyns, Michael ULg; Limbourg, Sabine ULg; Laporte, Gilbert

E-print/Working paper (2012)

Detailed reference viewed: 58 (10 ULg)
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See detailAutomatic Aircraft Load Planning
Limbourg, Sabine ULg; Schyns, Michael ULg; Laporte, Gilbert

in Journal of the Operational Research Society (2012), 63

The goal of this paper is the development of a new mixed integer linear program designed for optimally loading a set of containers and pallets into a compartmentalised cargo aircraft. It is based on real ... [more ▼]

The goal of this paper is the development of a new mixed integer linear program designed for optimally loading a set of containers and pallets into a compartmentalised cargo aircraft. It is based on real-world problems submitted by a professional partner. This model takes into account strict technical and safety constraints. In addition to the standard goal of optimally positioning the centre of gravity, we also propose a new approach based on the moment of inertia. This double goal implies an increase in aircraft efficiency and a decrease in fuel consumption. Cargo loading generally remains a manual, or at best a computer assisted, and time consuming task. A fully automatic software was developed to quickly compute optimal solutions. Experimental results show that our approach achieves better solutions than manual planning, within only a few seconds. [less ▲]

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See detailChargement d’un avion cargo : le cas des marchandises nécessitant des précautions particulières
Kleyntssens, Thomas ULg; Limbourg, Sabine ULg; Schyns, Michael ULg

Conference (2011, December 15)

Le problème du chargement de marchandises dans un avion cargo est soumis à des contraintes strictes de sécurité. C’est un problème d’optimisation combinatoire d’une importance cruciale pour les compagnies ... [more ▼]

Le problème du chargement de marchandises dans un avion cargo est soumis à des contraintes strictes de sécurité. C’est un problème d’optimisation combinatoire d’une importance cruciale pour les compagnies aériennes. En effet, un mauvais chargement diminue l’efficacité d’un avion et impose des tensions importantes sur sa structure qui peuvent entraîner la destruction d’équipements de haute valeur, voire la perte de vies. De plus, certains colis spéciaux ont des contraintes très restrictives. C’est le cas notamment des produits dangereux, des animaux, des marchandises alimentaires et périssables. En plus des incompatibilités entre certains produits, il faut tenir compte des interactions possibles sur des équipements de l’avion. Par exemple, des produits émettant des émissions magnétiques doivent être placés de manière à ne pas avoir des effets néfastes avec les instruments de navigation. Dans cet article, nous proposons d’incorporer ces contraintes liées aux colis nécessitant des précautions particulières dans un programme d’optimisation linéaire mixte du problème de chargement d’un ensemble de Unit Loading Devices et de vrac dans un avion. Les résultats obtenus à partir de données réelles montrent que notre méthode permet d’obtenir des solutions optimales en seulement quelques secondes. [less ▲]

Detailed reference viewed: 149 (9 ULg)
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See detailThree Dimensional Bin Packing Problem applied to air cargo
Paquay, Célia ULg; Schyns, Michael ULg; Limbourg, Sabine ULg

Scientific conference (2011, December 15)

Deciding whether a set of three dimensional boxes can be packed into a container is a NP-hard problem. Mathematical models have been developed, however, only few studies take into account constraints ... [more ▼]

Deciding whether a set of three dimensional boxes can be packed into a container is a NP-hard problem. Mathematical models have been developed, however, only few studies take into account constraints encountered in real-world applications such as the stability or the fragility of the cargo. Moreover, despite the importance of this issue in air transport, the literature is almost silent on constraints related to the distribution of the weight inside a container. This paper is concerned with the formulation of the three dimensional palletization which includes the main constraints met in the air cargo industry. [less ▲]

Detailed reference viewed: 126 (12 ULg)
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See detailLes défis du transport de fret
Limbourg, Sabine ULg; Schyns, Michael ULg

Article for general public (2011)

Detailed reference viewed: 88 (12 ULg)
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See detailAutomatic Cargo Load Planning: Special shipments
Limbourg, Sabine ULg; Schyns, Michael ULg

Scientific conference (2011, May 25)

The aircraft loading problem is a real-world combinatorial optimisation problem highly constrained. Indeed, loading the aircraft so the gross weight is less than the maximum allowable is not enough. This ... [more ▼]

The aircraft loading problem is a real-world combinatorial optimisation problem highly constrained. Indeed, loading the aircraft so the gross weight is less than the maximum allowable is not enough. This weight must be distributed to keep the centre of gravity (CG) within specified limits. Moreover, an aircraft has usually several cargo compartments with specific contours and structural limitations such as floor loading, combined load limits and cumulative load limitations. Finally, some shipments are particularly restrictive to transport, like dangerous goods, live animals and perishable goods. This paper is concerned with the incorporation of these latter constraints in a mixed integer linear program for the problem of loading a set of Unit Loading Devices (ULDs) and bulk into an aircraft. Experimental results for real data sets show that the model achieves better balanced solutions in only a few seconds compared to the solution obtained by load masters. [less ▲]

Detailed reference viewed: 29 (0 ULg)
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See detailAutomatic Cargo Load Planning: Special shipments
Limbourg, Sabine ULg; Schyns, Michael ULg

in Cornelis, Eric (Ed.) Proceedings of the BIVEC-GIBET Transport Research Day 2011 (2011)

The aircraft loading problem is a real-world combinatorial optimisation problem highly constrained. Indeed, loading the aircraft so the gross weight is less than the maximum allowable is not enough. This ... [more ▼]

The aircraft loading problem is a real-world combinatorial optimisation problem highly constrained. Indeed, loading the aircraft so the gross weight is less than the maximum allowable is not enough. This weight must be distributed to keep the centre of gravity (CG) within specified limits. Moreover, an aircraft has usually several cargo compartments with specific contours and structural limitations such as floor loading, combined load limits and cumulative load limitations. Finally, some shipments are particularly restrictive to transport, like dangerous goods, live animals and perishable goods. This paper is concerned with the incorporation of these latter constraints in a mixed integer linear program for the problem of loading a set of Unit Loading Devices (ULDs) and bulk into an aircraft. Experimental results for real data sets show that the model achieves better balanced solutions in only a few seconds compared to the solution obtained by load masters. [less ▲]

Detailed reference viewed: 47 (8 ULg)
See detailAircraft Cargo AutoLoad
Schyns, Michael ULg; Limbourg, Sabine ULg

Conference (2011, May)

Detailed reference viewed: 26 (4 ULg)
See detailPlanification automatique de chargements d'avions cargo
Limbourg, Sabine ULg; Schyns, Michael ULg

Scientific conference (2011, April 18)

Detailed reference viewed: 22 (0 ULg)
See detailIdentification du profil du consommateur par datamining
Schyns, Michael ULg

Scientific conference (2011, April)

Detailed reference viewed: 58 (4 ULg)
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See detailAutomatic Cargo Load Planning
Limbourg, Sabine ULg; Schyns, Michael ULg; Laporte, Gilbert

in Proceedings (2011, March 02)

The goal of this paper is the development of a new mixed integer linear pro- gram designed for optimally loading a set of containers and pallets into a compartmentalised cargo aircraft. It is based on ... [more ▼]

The goal of this paper is the development of a new mixed integer linear pro- gram designed for optimally loading a set of containers and pallets into a compartmentalised cargo aircraft. It is based on real-world problems submitted by a professional partner. This model takes into account strict technical and safety constraints. In addition to the standard goal of optimally positioning the centre of gravity, we also propose a new approach based on the moment of inertia. This double goal implies an increase in aircraft efficiency and a decrease in fuel consumption. Cargo loading generally remains a manual, or at best a computer assisted, and time consuming task. A fully automatic software was developed to quickly compute optimal solutions. Experimental results show that our approach achieves better solutions than manual planning, within only a few seconds. [less ▲]

Detailed reference viewed: 66 (12 ULg)
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See detailIntroduction à l'informatique en Sciences Sociales
Schyns, Michael ULg

Learning material (2010)

Detailed reference viewed: 46 (3 ULg)
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See detailRelaxMCD: smooth optimisation for the Minimum Covariance Determinant estimator
Schyns, Michael ULg; Haesbroeck, Gentiane ULg; Critchley, Frank

in Computational Statistics & Data Analysis (2010), 54(4), 843-857

The Minimum Covariance Determinant (MCD) estimator is a highly robust procedure for estimating the center and shape of a high dimensional data set. It consists of determining a subsample of h points out ... [more ▼]

The Minimum Covariance Determinant (MCD) estimator is a highly robust procedure for estimating the center and shape of a high dimensional data set. It consists of determining a subsample of h points out of n which minimizes the generalized variance. By definition, the computation of this estimator gives rise to a combinatorial optimization problem, for which several approximative algorithms have been developed. Some of these approximations are quite powerful, but they do not take advantage of any smoothness in the objective function. In this paper, focus is on the approach outlined in a general framework in Critchley et al. (2009) and which transforms any discrete and high dimensional combinatorial problem of this type into a continuous and low-dimensional one. The idea is to build on the general algorithm proposed by Critchley et al. (2009) in order to take into account the particular features of the MCD methodology. More specifically, both the adaptation of the algorithm to the specific MCD target function as well as the comparison of this “specialized” algorithm with the usual competitors for computing MCD are the main goals of this paper. The adaptation focuses on the design of “clever” starting points in order to systematically investigate the search domain. Accordingly, a new and surprisingly efficient procedure based on the well known k-means algorithm is constructed. The adapted algorithm, called RelaxMCD, is then compared by means of simulations and examples with FASTMCD and the Feasible Subset Algorithm, both benchmark algorithms for computing MCD. As a by-product, it is shown that RelaxMCD is a general technique encompassing the two others, yielding insight about their overall good performance. [less ▲]

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See detailA relaxed approach to combinatorial problems in robustness and diagnostics
Critchley, Frank; Schyns, Michael ULg; Haesbroeck, Gentiane ULg et al

in Statistics and Computing (2010), 20(1), 99-115

A range of procedures in both robustness and diagnostics require optimisation of a target functional over all subsamples of given size. Whereas such combinatorial problems are extremely difficult to solve ... [more ▼]

A range of procedures in both robustness and diagnostics require optimisation of a target functional over all subsamples of given size. Whereas such combinatorial problems are extremely difficult to solve exactly, something less than the global optimum can be ‘good enough’ for many practical purposes, as shown by example. Again, a relaxation strategy embeds these discrete, high-dimensional problems in continuous, low-dimensional ones. Overall, nonlinear optimisation methods can be exploited to provide a single, reasonably fast algorithm to handle a wide variety of problems of this kind, thereby providing a certain unity. Four running examples illustrate the approach. On the robustness side, algorithmic approximations to minimum covariance determinant (MCD) and least trimmed squares (LTS) estimation. And, on the diagnostic side, detection of multiple multivariate outliers and global diagnostic use of the likelihood displacement function. This last is developed here as a global complement to Cook’s (in J. R. Stat. Soc. 48:133–169, 1986) local analysis. Appropriate convergence of each branch of the algorithm is guaranteed for any target functional whose relaxed form is—in a natural generalisation of concavity, introduced here—‘gravitational’. Again, its descent strategy can downweight to zero contaminating cases in the starting position. A simulation study shows that, although not optimised for the LTS problem, our general algorithm holds its own with algorithms that are so optimised. An adapted algorithm relaxes the gravitational condition itself. [less ▲]

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See detailA robust heuristic for the optimal selection of a portfolio of stocks
Schyns, Michael ULg

in International Journal of Operational Research (2010), 9(3), 258-271

This paper introduces a new optimization heuristic for the robustification of critical inputs under consideration in many problems. It is shown that it allows to improve significantly the quality and the ... [more ▼]

This paper introduces a new optimization heuristic for the robustification of critical inputs under consideration in many problems. It is shown that it allows to improve significantly the quality and the stability of the results for two classical financial problems, i.e. the Markowitz' portfolio selection problem and the computation of the financial beta. Focus here is on the robust Minimum Covariance Determinant (MCD) estimator which can easily be substituted to the classical estimators of location and scatter. By definition, the computation of this estimator gives rise to a combinatorial optimization problem. We present a new heuristic, called 'RelaxMCD', which is based on a relaxation of the problem to the continuous space. The utility of this approach and the performance of our heuristic, with respect to other competitors, are illustrated through extensive simulations. [less ▲]

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See detailOptimal selection of a portfolio of options under Value-at-Risk constraints: a scenario approach
Schyns, Michael ULg; Crama, Yves ULg; Hübner, Georges ULg

in Annals of Operations Research (2010), 181

This paper introduces a multiperiod model for the optimal selection of a financial portfolio of options linked to a single index. The objective of the model is to maximize the expected return of the ... [more ▼]

This paper introduces a multiperiod model for the optimal selection of a financial portfolio of options linked to a single index. The objective of the model is to maximize the expected return of the portfolio under constraints limiting its Value-at-Risk. We rely on scenarios to represent future security prices. The model contains several interesting features, like the consideration of transaction costs, bid-ask spreads, arbitrage-free option pricing, and the possibility to rebalance the portfolio with options introduced at the start of each period. The resulting mixed integer programming model is applied to realistic test instances involving options on the S&P500 index. In spite of the large size and of the numerical difficulty of this model, near-optimal solutions can be computed by a standard branch-and-cut solver or by a specialized heuristic. The structure and the financial features of the selected portfolios are also investigated. [less ▲]

Detailed reference viewed: 100 (26 ULg)
See detailRAPPORT DE RECHERCHE SUR UNE APPLICATION DE GESTION DE LA COLLABORATION DU SERVICE EXPÉDITION DU CHARGEUR AVEC LE TRANSPORTEUR
Pironet, Thierry ULg; Crama, Yves ULg; Arda, Yasemin ULg et al

Report (2009)

Dans ce rapport, les échanges d'information d'un donneur d'ordre, d'un transporteur et d'un fournisseur au sein d'une chaîne de distribution sont analysés. Les possibilités de tracking et de tracing de ... [more ▼]

Dans ce rapport, les échanges d'information d'un donneur d'ordre, d'un transporteur et d'un fournisseur au sein d'une chaîne de distribution sont analysés. Les possibilités de tracking et de tracing de TransLogisTIC sont utilisés pour générer des KPI de performance et un modèle d'optimisation de quais de chargement est décrit dans une version Off-line et On-line. [less ▲]

Detailed reference viewed: 146 (31 ULg)
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See detailInformatique en Sciences de Gestion et en Sciences Economiques - Niveau 2
Schyns, Michael ULg

Learning material (2009)

Detailed reference viewed: 21 (4 ULg)