References of "Crama, Yves"
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See detailVehicle loading optimization with stochastic supply
Amand, Guillaume ULg; Arda, Yasemin ULg; Crama, Yves ULg et al

Conference (2010, January 29)

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See detailBoolean Models and Methods in Mathematics, Computer Science, and Engineering
Crama, Yves ULg; Hammer, Peter L.

Book published by Cambridge University Press (2010)

This collection of papers proposes in-depth presentations of a variety of advanced topics related to Boolean functions and expressions. The chapters are written by some of the most prominent experts in ... [more ▼]

This collection of papers proposes in-depth presentations of a variety of advanced topics related to Boolean functions and expressions. The chapters are written by some of the most prominent experts in their respective fields, and cover topics ranging from algebra and propositional logic to learning theory, cryptography, computational complexity, electrical engineering, and reliability theory. Beyond the diversity of the questions raised and investigated in different chapters, a remarkable feature of the collection is the common thread created by the fundamental language, concepts, models and tools provided by Boolean theory. Many readers will certainly be surprised to discover countless links between seemingly remote topics discussed in various chapters of the book. They will hopefully be able to draw on such connections to further their understanding of their own scientific discipline and to explore new avenues for research. [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 ▲]

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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 ▲]

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See detailVehicle loading optimization with stochastic supply
Amand, Guillaume ULg; Arda, Yasemin ULg; Crama, Yves ULg et al

Conference (2009, July 07)

The increased availability of information makes it possible to coordinate processes which are usually functionnally separated in large companies, such as production and transportation. This work ... [more ▼]

The increased availability of information makes it possible to coordinate processes which are usually functionnally separated in large companies, such as production and transportation. This work investigates the optimization of vehicle loading for individual orders over a multiperiod horizon when items have stochastic release dates from production, and time windows are imposed for delivery at the customer plant. The loading decisions are made in order to minimize the expected cost. Starting from the deterministic model, we develop scenario-based models for the stochastic version of the problem and we investigate the performance of various solution methods. [less ▲]

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See detailLocal search heuristics for large-scale discrete structural optimization with expensive black-box evaluations
Bay, Maud ULg; Crama, Yves ULg; Rigo, Philippe ULg

Report (2009)

This paper considers large-scale structural optimization problems featuring discrete variables, as well as nonlinear implicit constraints which can only be evaluated through time-expensive computations. A ... [more ▼]

This paper considers large-scale structural optimization problems featuring discrete variables, as well as nonlinear implicit constraints which can only be evaluated through time-expensive computations. A prominent application consists in the preliminary structural design of large ships, where many of the variables take their values in discrete sets which model standard element dimensions to be selected from catalogs, and where the evaluation of the constraints involves a complex structural analysis performed by black-box software. The resulting large-scale nonlinear combinatorial problems are particularly hard, and even nding a discrete feasible solution may prove challenging for some instances. In this paper, we propose two heuristics that combine local search methods and a sequential optimization method based on approximations of the implicit constraints. The heuristics are applied to the structural optimization of several large ships. For these instances, the heuristics provide discrete feasible solutions whose value is close to the optimal value of the continuous relaxation obtained by disregarding the discrete nature of the variables. [less ▲]

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See detailRAPPORT INTERNE : REVUE DE LITTERATURE SUR LA GESTION DES RESSOURCES RÉUTILISABLES ET DES MÉTHODES D’OPTIMISATION
Pironet, Thierry ULg; Crama, Yves ULg; Arda, Yasemin ULg et al

Report (2009)

Dans cette revue de la littérature scientifique, on peut trouver une synthèse des thématiques liées aux modèles et aux techniques d'optimisation utilés pour la gestion de ressources réutilisables dans un ... [more ▼]

Dans cette revue de la littérature scientifique, on peut trouver une synthèse des thématiques liées aux modèles et aux techniques d'optimisation utilés pour la gestion de ressources réutilisables dans un réseau tels que les containers entre des ports de mers ou des wagons dans un réseau ferroviaire. Les textes fondateurs sont mentionnés dans un ordre historique et un commentaire est fait soit sur le modèle investiqué et ses particularités ou la technique de résolution. [less ▲]

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See detailAlternative to the Mean-Variance Asset Allocation Analysis: A Scenario Methodology for Portfolio Selection
Schyns, Michael ULg; Hübner, Georges ULg; Crama, Yves ULg

in Gregoriou, Greg N. (Ed.) Stock Market Volatility (2009)

This paper introduces a new methodology to optimize the allocation of financial assets. The objective of the model is to maximize the expected return of the portfolio under constraints limiting its Value ... [more ▼]

This paper introduces a new methodology to optimize the allocation of financial assets. The objective of the model is to maximize the expected return of the portfolio under constraints limiting its Value-at-Risk. The assets could consist in stocks as well as options. We rely on a flexible scenario tree approach to represent the future prices. In order to reduce the number of leaves and maintain the model tractable, stocks prices are obtained through the Fama & French empirical asset pricing model. Experiments on historical data are performed to illustrate the method and show the performance of the approach. Different strategies are compared: considering various market distributions, several factor models and a few portfolio hypothesis. [less ▲]

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See detailRAPPORT DE RECHERCHE SUR L’OPTIMISATION DU ROUTAGE ET DU CHARGEMENT DE VEHICULES.
Pironet, Thierry ULg; Crama, Yves ULg; Arda, Yasemin ULg et al

Report (2009)

Dans ce rapport confidentiel, un algorithme d'optimisation du chargement de véhicules a été mis au point dans le cadre d'une application avec un partenaire industriel.

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See detailUn problème de chargement/déchargement profitable d'une flotte de véhicules soumise à des fenêtres de temps
Arda, Yasemin ULg; Crama, Yves ULg; Pironet, Thierry ULg

Conference (2008, February 26)

In most pickup and delivery problems, usually the aim is to minimize either the trip length or duration or the fleet size. Transportation orders or customers are finite sets which should be performed or ... [more ▼]

In most pickup and delivery problems, usually the aim is to minimize either the trip length or duration or the fleet size. Transportation orders or customers are finite sets which should be performed or visited integraly. So, the total earning is supposed to be constant. Conversely, the costs related to trip length or duration or either to the fleet size are consequences of the operations management efficiency. Therefore, typically the objective function is reduced to a cost minimization. On the contrary, this model tends to maximize the global profit. Let’s consider a fleet of vehicles starting at different initial times from different locations and oblige to return to their final depots before fixed maximal times. On their way-back, these vehicles are performing full-truck-load transportation between pickup and delivery points and have to respect time windows for the loading and unloading operations. Realized transportation orders add positive contributions while linking paths generate costs. In summary, the goal for the fleet resides in the selection of transportations orders among available ones while fullfilling the final time requirements and the time restrictions for the un/loading operations. [less ▲]

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See detailA profitable pickup and delivery problem with time windows
Arda, Yasemin ULg; Crama, Yves ULg; Pironet, Thierry ULg

Conference (2008, January 18)

In most pickup and delivery problems, usually the aim is to minimize either the trip length or duration or the fleet size. Transportation orders or customers are finite sets which should be performed or ... [more ▼]

In most pickup and delivery problems, usually the aim is to minimize either the trip length or duration or the fleet size. Transportation orders or customers are finite sets which should be performed or visited integraly. So, the total earning is supposed to be constant. Conversely, the costs related to trip length or duration or either to the fleet size are consequences of the operations management efficiency. Therefore, typically the objective function is reduced to a cost minimization. On the contrary, this model tends to maximize the global profit. Let’s consider a fleet of vehicles starting at different initial times from different locations and oblige to return to their final depots before fixed maximal times. On their way-back, these vehicles are performing full-truck-load transportation between pickup and delivery points and have to respect time windows for the loading and unloading operations. Realized transportation orders add positive contributions while linking paths generate costs. In summary, the goal for the fleet resides in the selection of transportations orders among available ones while fullfilling the final time requirements and the time restrictions for the un/loading operations. [less ▲]

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See detailCounting and enumerating aggregate classifiers
Adem, Jan; Crama, Yves ULg; Gochet, Willy et al

in Discrete Applied Mathematics (2008), 156(3), 2459-2468

We propose a generic model for the "weighted voting" aggregation step performed by several methods in supervised classification. Further, we construct an algorithm to count the number of distinct ... [more ▼]

We propose a generic model for the "weighted voting" aggregation step performed by several methods in supervised classification. Further, we construct an algorithm to count the number of distinct aggregate classifiers that arise in this model. When there are only two classes in the classification problem, we show that a class of functions that arises from aggregate classifiers coincides with the class of self-dual positive threshold Boolean functions. [less ▲]

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See detailModèles et données dans l’univers économique
Bair, Jacques ULg; Crama, Yves ULg

in Justens, Daniel (Ed.) Attentes d'un modèle (2008)

Dans cette note, nous émettons quelques réflexions relatives à la modélisation scientifique, en insistant sur la spécificité de l'exploitation de modèles dans les sciences humaines, en particulier en ... [more ▼]

Dans cette note, nous émettons quelques réflexions relatives à la modélisation scientifique, en insistant sur la spécificité de l'exploitation de modèles dans les sciences humaines, en particulier en économie (au sens large du terme), par comparaison avec les sciences de la nature comme la physique, la biologie,... [less ▲]

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See detailGeršgorin variations III: On a theme of Brualdi and Varga
Boros, Endre; Brualdi, Richard; Crama, Yves ULg et al

in Journal of Linear Algebra and its Applications (2008), 428

Brualdi brought to Geršgorin Theory the concept that the digraph G(A) of a matrix A is important in studying whether A is singular. He proved, for example, that if, for every directed cycle of G(A), the ... [more ▼]

Brualdi brought to Geršgorin Theory the concept that the digraph G(A) of a matrix A is important in studying whether A is singular. He proved, for example, that if, for every directed cycle of G(A), the product of the diagonal entries exceeds the product of the row sums of the moduli of the off-diagonal entries, then the matrix is nonsingular. We will show how, in polynomial time, that condition can be tested and (if satisfied) produce a diagonal matrix D, with positive diagonal entries, such that AD (where A is any nonnnegative matrix satisfying the conditions) is strictly diagonally dominant (and so, A is nonsingular). The same D works for all matrices satisfying the conditions. Varga raised the question of whether Brualdi’s conditions are sharp. Improving Varga’s results, we show, if G is scwaltcy (strongly connected with at least two cycles), and if the Brualdi conditions do not hold, how to construct (again in polynomial time) a complex matrix whose moduli satisfy the given specifications, but is singular. [less ▲]

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See detailPractical methods for measuring and managing operational risk in the financial sector: A clinical study
Chapelle, Ariane; Crama, Yves ULg; Hübner, Georges ULg et al

in Journal of Banking and Finance (2008), 32

This paper analyzes the implications of the Advanced Measurement Approach (AMA) for the assessment of operational risk. Through a clinical case study on a matrix of two selected business lines and two ... [more ▼]

This paper analyzes the implications of the Advanced Measurement Approach (AMA) for the assessment of operational risk. Through a clinical case study on a matrix of two selected business lines and two event types of a large financial institution, we develop a procedure that addresses the major issues faced by banks in the implementation of the AMA. For each cell, we calibrate two truncated distributions functions, one for “normal” losses and the other for the “extreme” losses. In addition, we propose a method to include external data in the framework. We then estimate the impact of operational risk management on bank profitability, through an adapted measure of RAROC. The results suggest that substantial savings can be achieved through active management techniques. [less ▲]

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See detailThe tool switching problem revisited
Crama, Yves ULg; Moonen, Linda S; Spieksma, Frits CR et al

in European Journal of Operational Research (2007), 182(2), 952-957

In this note we study the tool switching problem with non-uniform tool sizes. More specifically, we consider the problem where the job sequence is given as part of the input. We show that the resulting ... [more ▼]

In this note we study the tool switching problem with non-uniform tool sizes. More specifically, we consider the problem where the job sequence is given as part of the input. We show that the resulting tooling problem is strongly N P-complete, even in case of unit loading and unloading costs. On the other hand, if the capacity of the tool magazine is also given as part of the input, we show that the problem is solvable in polynomial time. These results settle the complexity of a relevant variant of the tool switching problem. (C) 2006 Elsevier B.V. All rights reserved. [less ▲]

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See detailControl and voting power in corporate networks: Concepts and computational aspects
Crama, Yves ULg; Leruth, Luc ULg

in European Journal of Operational Research (2007), 178(3), 879-893

This paper proposes to rely on power indices to measure the amount of control held by individual shareholders in corporate networks. The value of the indices is determined by a complex voting game viewed ... [more ▼]

This paper proposes to rely on power indices to measure the amount of control held by individual shareholders in corporate networks. The value of the indices is determined by a complex voting game viewed as the composition of interlocked weighted majority games; the compound game reflects the structure of shareholdings. The paper describes an integrated algorithmic approach which allows to deal efficiently with the complexity of computing power indices in shareholding networks, irrespective of their size or structure. In particular, the approach explicitly accounts for the presence of float and of cyclic shareholding relationships. It has been successfully applied to the analysis of real-world financial networks. (c) 2006 Elsevier B.V. All rights reserved. [less ▲]

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See detailA mixed-integer heuristic for the structural optimization of a cruise ship
Bay, Maud ULg; Crama, Yves ULg; Richir, Thomas et al

in COMPIT 2007 , Cortona, Italy (2007, April 23)

A heuristic approach is proposed to solve the structural optimization problem of a cruise ship. The challenge of optimization is to define the scantling of the structure of a ship in order to minimize the ... [more ▼]

A heuristic approach is proposed to solve the structural optimization problem of a cruise ship. The challenge of optimization is to define the scantling of the structure of a ship in order to minimize the weight or the production cost. The variables are the dimensions and positions of the constitutive elements of the structure: they are discrete by nature. The objective functions are nonlinear functions. The structure is submitted to geometric constraints and to structural constraints. The geometric constraints are linear functions and the structural constraints are implicit functions requiring a high computation cost. The problem belongs to the class of mixed-integer nonlinear problems (MINLP). A local heuristic of the type “dive and fix” is combined with a solver based on approximation methods. The solver is used as a black-box tool to perform the structural analysis and solve the nonlinear optimization problems (NLP) defined by the heuristic. The heuristic is designed to always provide a discrete feasible solution. Experiments on a real-size structure demonstrate that the optimal value of the mixed-integer problem is of the same magnitude as the optimal value of the optimization problem for which all the variables can take continuous values. [less ▲]

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See detailPeter Ladislaw Hammer (1936-2006)
Boros, Endre; Crama, Yves ULg; Simeone, Bruno

in 4OR : Quarterly Journal of the Belgian, French and Italian Operations Research Societies (2007), 5(1), 1-4

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See detailMultiplicity and complexity issues in contemporary production scheduling
Brauner, Nadia; Crama, Yves ULg; Grigoriev, Alexander et al

in Statistica Neerlandica (2007), 61(1), 75-91

High multiplicity scheduling problems arise naturally in contemporary production settings where manufacturers combine economies of scale with high product variety. Despite their frequent occurrence in ... [more ▼]

High multiplicity scheduling problems arise naturally in contemporary production settings where manufacturers combine economies of scale with high product variety. Despite their frequent occurrence in practice, the complexity of high multiplicity problems - as opposed to classical, single multiplicity problems - is in many cases not well understood. In this paper, we discuss various concepts and results that enable a better understanding of the nature and complexity of high multiplicity scheduling problems. The paper extends the framework presented in Brauner et al. [Journal of Combinatorial Optimization (2005) Vol. 9, pp. 313-323] for single machine, non-preemptive high multiplicity scheduling problems, to more general classes of problems. [less ▲]

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