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See detailApproximate value iteration in the reinforcement learning context. Application to electrical power system control
Ernst, Damien ULg; Glavic, Mevludin; Geurts, Pierre ULg et al

in International Journal of Emerging Electrical Power Systems (2005), 3(1),

In this paper we explain how to design intelligent agents able to process the information acquired from interaction with a system to learn a good control policy and show how the methodology can be applied ... [more ▼]

In this paper we explain how to design intelligent agents able to process the information acquired from interaction with a system to learn a good control policy and show how the methodology can be applied to control some devices aimed to damp electrical power oscillations. The control problem is formalized as a discrete-time optimal control problem and the information acquired from interaction with the system is a set of samples, where each sample is composed of four elements: a state, the action taken while being in this state, the instantaneous reward observed and the successor state of the system. To process this information we consider reinforcement learning algorithms that determine an approximation of the so-called Q-function by mimicking the behavior of the value iteration algorithm. Simulations are first carried on a benchmark power system modeled with two state variables. Then we present a more complex case study on a four-machine power system where the reinforcement learning algorithm controls a Thyristor Controlled Series Capacitor (TCSC) aimed to damp power system oscillations. [less ▲]

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See detailApproximating Functions on a Mesh with Restricted Voronoï Diagrams
Nivoliers, Vincent ULg; Lévy, Bruno

in Computer Graphics Forum (2013), 32(5), 83-92

We propose a method that computes a piecewise constant approximation of a function defined on a mesh. The approximation is associated with the cells of a restricted Voronoï diagram. Our method optimizes ... [more ▼]

We propose a method that computes a piecewise constant approximation of a function defined on a mesh. The approximation is associated with the cells of a restricted Voronoï diagram. Our method optimizes an objective function measuring the quality of the approximation. This objective function depends on the placement of the samples that define the restricted Voronoï diagram and their associated function values. We study the continuity of the objective function, derive the closed-form expression of its derivatives and use them to design a numerical solution mechanism. The method can be applied to a function that has discontinuities, and the result aligns the boundaries of the Voronoï cells with the discontinuities. Some examples are shown, suggesting potential applications in image vectorization and compact representation of lighting. [less ▲]

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See detailApproximation Algorithms for Multi-Dimensional Vector Assignment Problems
Dokka, Trivikram; Crama, Yves ULg; Spieksma, Frits C.R.

E-print/Working paper (2013)

We consider a special class of axial multi-dimensional assignment problems called multi-dimensional vector assignment (MVA) problems. An instance of the MVA problem is defined by $m$ disjoint sets, each ... [more ▼]

We consider a special class of axial multi-dimensional assignment problems called multi-dimensional vector assignment (MVA) problems. An instance of the MVA problem is defined by $m$ disjoint sets, each of which contains the same number $n$ of $p$-dimensional vectors with nonnegative integral components, and a cost function defined on vectors. The cost of an $m$-tuple of vectors is defined as the cost of their component-wise maximum. The problem is now to partition the $m$ sets of vectors into $n$ $m$-tuples so that no two vectors from the same set are in the same $m$-tuple and so that the total cost of the $m$-tuples is minimized. The main motivation comes from a yield optimization problem in semi-conductor manufacturing. We consider two classes of polynomial-time heuristics for MVA, namely, hub heuristics and sequential heuristics, and we study their approximation ratio. In particular, we show that when the cost function is monotone and subadditive, hub heuristics, as well as sequential heuristics, have finite approximation ratio for every fixed $m$. Moreover, we establish better approximation ratios for certain variants of hub heuristics and sequential heuristics when the cost function is monotone and submodular, or when it is additive. We provide examples to illustrate the tightness of our analysis. Furthermore, we show that the MVA problem is APX-hard even for the case $m=3$ and for binary input vectors. Finally, we show that the problem can be solved in polynomial time in the special case of binary vectors with fixed dimension $p$. [less ▲]

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See detailApproximation algorithms for multi-dimensional vector assignment problems
Crama, Yves ULg

Conference (2014, July 09)

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See detailApproximation Algorithms for Multi-Dimensional Vector Assignment Problems
Crama, Yves ULg

Conference (2013, July 04)

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See detailApproximation algorithms for the design of SDH/SONET networks
Brauner, Nadia; Crama, Yves ULg; Finke, Gerd et al

in RAIRO : Operations Research = Recherche Opérationnelle (2003), 37(4, OCT-DEC), 235-247

In this paper, a graph partitioning problem that arises in the design of SONET/SDH networks is defined and formalized. Approximation algorithms with performance guarantees are presented. To solve this ... [more ▼]

In this paper, a graph partitioning problem that arises in the design of SONET/SDH networks is defined and formalized. Approximation algorithms with performance guarantees are presented. To solve this problem efficiently in practice, fast greedy algorithms and a tabu-search method are proposed and analyzed by means of an experimental study. [less ▲]

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See detailApproximation efficace de mélanges bootstrap d’arbres de Markov pour l’estimation de densité
Schnitzler, François ULg; Ammar, Sourour; Leray, Philippe et al

in Bougrain, Laurent (Ed.) Actes de la 14e Conférence Francophone sur l'Apprentissage Automatique (CAp 2012) (2012, May 23)

Nous considérons des algorithmes pour apprendre des Mélanges bootstrap d'Arbres de Markov pour l'estimation de densité. Pour les problèmes comportant un grand nombre de variables et peu d'observations ... [more ▼]

Nous considérons des algorithmes pour apprendre des Mélanges bootstrap d'Arbres de Markov pour l'estimation de densité. Pour les problèmes comportant un grand nombre de variables et peu d'observations, ces mélanges estiment généralement mieux la densité qu'un seul arbre appris au maximum de vraisemblance, mais sont plus coûteux à apprendre. C'est pourquoi nous étudions ici un algorithme pour apprendre ces modèles de manière approchée, afin d'accélérer l'apprentissage sans sacrifier la précision. Plus spécifiquement, nous récupérons lors du calcul d'un premier arbre de Markov les arcs qui constituent de bons candidats pour la structure, et ne considérons que ceux-ci lors de l'apprentissage des arbres suivants. Nous comparons cet algorithme à l'algorithme original de mélange, à un arbre appris au maximum de vraisemblance, à un arbre régularisé et à une autre méthode approchée. [less ▲]

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See detailApproximation of reliability for multiple-trait animal models with missing data by canonical transformation
Gengler, Nicolas ULg; Misztal, I.

in Journal of Dairy Science (1996), 79(2), 317-328

An algorithm for approximation of reliability for multiple traits by multiple diagonalization was modified to support missing data by weighting transformed contributions of records based on the pattern of ... [more ▼]

An algorithm for approximation of reliability for multiple traits by multiple diagonalization was modified to support missing data by weighting transformed contributions of records based on the pattern of missing data. The accuracy of approximation was assessed with simulated and field data by comparing approximate reliabilities with those from direct inversion. Simulated data had several levels of missing data and covariances between traits; correlations were close to those for linear type traits of dairy cattle. Field data were 1) dairy records for milk, fat, and protein yields with 26% of the observations for fat and protein removed and 2) beef records for birth weight, weaning weight, and mean gain after weaning with 43% of observations missing. These files also contained empty fixed effect classes. The algorithm worked best for simulated data, and, when covariances between traits decreased, proportion of missing traits decreased and the number of empty fixed classes decreased. For dairy data, improvement over single-trait reliability occurred only for traits with missing data; for beef data, little or no improvement occurred. The method is useful with multiple diagonalization if the proportion of missing records or number of empty fixed effect classes or covariances between traits is moderate. [less ▲]

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See detailApproximations and their consequences for dynamic modelling of signal transduction pathways
Millat, Thomas; Bullinger, Eric ULg; Rohwer, Johann et al

in Mathematical Biosciences (2007), 207(1), 40-57

Signal transduction is the process by which the cell converts one kind of signal or stimulus into another. This involves a sequence of biochemical reactions, carried out by proteins. The dynamic response ... [more ▼]

Signal transduction is the process by which the cell converts one kind of signal or stimulus into another. This involves a sequence of biochemical reactions, carried out by proteins. The dynamic response of complex cell signalling networks can be modelled and simulated in the framework of chemical kinetics. The mathematical formulation of chemical kinetics results in a system of coupled differential equations. Simplifications can arise through assumptions and approximations. The paper provides a critical discussion of frequently employed approximations in dynamic modelling of signal transduction pathways. We discuss the requirements for conservation laws, steady state approximations, and the neglect of components. We show how these approximations simplify the mathematical treatment of biochemical networks but we also demonstrate differences between the complete system (c) 2006 Elsevier Inc. All rights reserved. [less ▲]

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See detailApproximations of Lovász extensions and their induced interaction index
Marichal, Jean-Luc; Mathonet, Pierre ULg

in Discrete Applied Mathematics (2008), 156(1), 11-24

The Lovasz extension of a pseudo-Boolean function f : (0, 1)(n) -> R is defined on each simplex of the standard triangulation of [0, 1](n) as the unique affine function (f) over cap : [0, 1](n) -> R that ... [more ▼]

The Lovasz extension of a pseudo-Boolean function f : (0, 1)(n) -> R is defined on each simplex of the standard triangulation of [0, 1](n) as the unique affine function (f) over cap : [0, 1](n) -> R that interpolates f at the n + 1 vertices of the simplex. Its degree is that of the unique multilinear polynomial that expresses f. In this paper we investigate the least squares approximation problem of an arbitrary Lovasz extension (f) over cap by Lovasz extensions of (at most) a specified degree. We derive explicit expressions of these approximations. The corresponding approximation problem for pseudo-Boolean functions was investigated by Hammer and Holzman [Approximations of pseudo-Boolean functions; applications to game theory, Z. Oper. Res. 36(1) (1992) 3-21] and then solved explicitly by Grabisch et al. [Equivalent representations of set functions, Math. Oper. Res. 25(2) (2000) 157-178], giving rise to an alternative definition of Banzhaf interaction index. Similarly we introduce a new interaction index from approximations of (f) over cap and we present some of its properties. It turns out that its corresponding power index identifies with the power index introduced by Grabisch and Labreuche [How to improve acts: an alternative representation of the importance of criteria in MCDM, Internat. J. Uncertain. Fuzziness Knowledge-Based Syst. 9(2) (2001) 145-157]. (c) 2007 Elsevier B.V. All rights reserved. [less ▲]

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See detailAppui à l'Assemblée nationale de la RDC
Kabamba, Bob ULg

Report (2010)

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See detailAppui à l'Assemblée provinciale de Bandundu
Kabamba, Bob ULg

Report (2011)

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See detailAppui à l'Assemblée provinciale de Maniema et Sud-Kivu
Kabamba, Bob ULg

Report (2010)

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See detailAppui à la création d’un diplôme d’études approfondies en biologie végétale et environnement à l’Université de Lubumbashi et remédiation multiscalaire des sols contaminés.
Ngongo Luhembwe, M; Bogaert, Jan ULg; Colinet, Gilles ULg et al

in Dahdouh-Guebas, F (Ed.) Proceedings of the Symposium on African Botany in Brussels (2009)

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See detailAppui à la gestion et à la protection des ressources en eau souterraines exploitées dans la région de Bobo Dioulasso (Burkina Faso) - Rapport d'activité N°6 rélatif aux subventions 2010-2011
Sauret, Elie ULg; Derouane, Johan; Brouyère, Serge ULg et al

Report (2011)

L’année 2011 correspond à la troisième année de la deuxième phase d’exécution du projet de coopération bilatérale entre le Burkina Faso et Wallonie-Bruxelles International intitulé « Appui à la gestion et ... [more ▼]

L’année 2011 correspond à la troisième année de la deuxième phase d’exécution du projet de coopération bilatérale entre le Burkina Faso et Wallonie-Bruxelles International intitulé « Appui à la gestion et à la protection des ressources en eaux souterraines exploitées dans la région de Bobo-Dioulasso ». L’exécution des activités de cette troisième année s’est étalée du 01 octobre 2010 au 31 octobre 2011. L’ensemble des activités réalisées et les résultats obtenus sont repris dans ce document de synthèse. [less ▲]

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See detailAppui à la gestion et à la protection des ressources en eaux souterraines exploitées dans la région de Bobo Dioulasso (Burkina Faso) – mise en place d’une base de données spatiales
Sauret, Elie ULg; Gardin, Nicolas; Kam, Ahmed et al

Conference (2011, November 03)

Située au sud ouest du Burkina Faso, dans la région de Bobo Dioulasso, le bassin du kou couvre 1860km2 de superficie et héberge d’énormes réservoirs en eau souterraines auxquels sont associés ... [more ▼]

Située au sud ouest du Burkina Faso, dans la région de Bobo Dioulasso, le bassin du kou couvre 1860km2 de superficie et héberge d’énormes réservoirs en eau souterraines auxquels sont associés d’importantes sources diffuses. Ces réserves en eau sont sollicitées pour l’alimentation en eau de boisson, l’industrie, l’agriculture irriguée et l’élevage ; elles ont été et demeure l’objet de nombreuses études touchant l’ingénierie de l’eau et des sols, l’imagerie satellitaire et géophysique, l’hydrochimie…. Depuis 2005, le projet de coopération bilatérale entre la WBI1 et le MAHRH-BF2 dénommé : « Appui à la gestion et à la protection des ressources en eaux souterraines exploitées dans la région de Bobo – Dioulasso » a permis de collecter, compiler et archiver des données (numériques, papiers, cartes…) qui ont servi à la construction d’une base de données spatiales couplées à un SIG (ArcGis). Des post-traitements de ces données ont permis l’établissement de cartes thématiques sur les ressources en eau de la région : carte hydrogéologique, carte de la vulnérabilité intrinsèque des aquifères souterrains, carte hydrogéomorphologique…….Utilisée au sein du projet pour les travaux de thèse en cours, la GDB des ressources en eau du bassin du Kou est largement vulgarisée et diffusée à l’échelle régionale et nationale aux utilisateurs et acteurs du domaine de l’eau. [less ▲]

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See detailAPPUI ANALYTIQUE A LA LUTTE CONTRE LES MEDICAMENTS DE QUALITE INFERIEURE
Mbinze Kindenge, Jérémie; Hubert, Philippe ULg; Marini Djang'Eing'A, Roland ULg

Conference (2015, January 27)

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See detailAppui au développement rural multisectoriel au Laos
Lebailly, Philippe ULg

in Premières rencontres internationales de la CUD "Construire ensemble le Savoir Universitaire pour le Développement" (2003)

Detailed reference viewed: 20 (5 ULg)