References of "Wehenkel, Louis"
     in
Bookmark and Share    
Full Text
Peer Reviewed
See detailA cautious approach to generalization in reinforcement learning
Fonteneau, Raphaël ULg; Murphy, Susan; Wehenkel, Louis ULg et al

in Proceedings of the 2nd International Conference on Agents and Artificial Intelligence (2010, January)

In the context of a deterministic Lipschitz continuous environment over continuous state spaces, finite action spaces, and a finite optimization horizon, we propose an algorithm of polynomial complexity ... [more ▼]

In the context of a deterministic Lipschitz continuous environment over continuous state spaces, finite action spaces, and a finite optimization horizon, we propose an algorithm of polynomial complexity which exploits weak prior knowledge about its environment for computing from a given sample of trajectories and for a given initial state a sequence of actions. The proposed Viterbi-like algorithm maximizes a recently proposed lower bound on the return depending on the initial state, and uses to this end prior knowledge about the environment provided in the form of upper bounds on its Lipschitz constants. It thereby avoids, in way depending on the initial state and on the prior knowledge, those regions of the state space where the sample is too sparse to make safe generalizations. Our experiments show that it can lead to more cautious policies than algorithms combining dynamic programming with function approximators. We give also a condition on the sample sparsity ensuring that, for a given initial state, the proposed algorithm produces an optimal sequence of actions in open-loop. [less ▲]

Detailed reference viewed: 85 (22 ULg)
Full Text
Peer Reviewed
See detailModel-free Monte Carlo-like policy evaluation
Fonteneau, Raphaël ULg; Murphy, Susan A.; Wehenkel, Louis ULg et al

in 29th Benelux Meeting on Systems and Control (2010)

Detailed reference viewed: 10 (1 ULg)
Full Text
See detailComputing bounds for kernel-based policy evaluation in reinforcement learning
Fonteneau, Raphaël ULg; Murphy, Susan A.; Wehenkel, Louis ULg et al

Report (2010)

This technical report proposes an approach for computing bounds on the finite-time return of a policy using kernel-based approximators from a sample of trajectories in a continuous state space and ... [more ▼]

This technical report proposes an approach for computing bounds on the finite-time return of a policy using kernel-based approximators from a sample of trajectories in a continuous state space and deterministic framework. [less ▲]

Detailed reference viewed: 14 (3 ULg)
Peer Reviewed
See detailRobust Automatic Target Recognition Using Extra-trees
Pisane, Jonathan ULg; Marée, Raphaël ULg; Wehenkel, Louis ULg et al

in Pisane, Jonathan (Ed.) Robust Automatic Target Recognition Using Extra-trees (2010)

In this paper, we describe a new automatic target recognition algorithm for classifying SAR images based on the PiXiT image classifier. It uses randomized sub-windows extraction and extremely randomized ... [more ▼]

In this paper, we describe a new automatic target recognition algorithm for classifying SAR images based on the PiXiT image classifier. It uses randomized sub-windows extraction and extremely randomized trees (extra-trees). This approach requires very little pre-processing of the images, thereby limiting the computational load. It was successfully tested on an extended version of the public standard MSTAR database, that includes targets of interest, false targets, and background clutter. A misclassification rate of about three percent has been achieved. [less ▲]

Detailed reference viewed: 114 (4 ULg)
Full Text
Peer Reviewed
See detailEditorial - Special Section on Processing and Analysis of High-Dimensional Masses of Image and Signal Data
Charrier, Christophe; Lézoray, Olivier; Elmoataz, Abderrahim et al

in Signal Processing (2010), 90(8), 2331-2332

Detailed reference viewed: 9 (0 ULg)
Full Text
Peer Reviewed
See detailTree based ensemble models regularization by convex optimization
Cornélusse, Bertrand ULg; Geurts, Pierre ULg; Wehenkel, Louis ULg

Conference (2009, December 12)

Tree based ensemble methods can be seen as a way to learn a kernel from a sample of input-output pairs. This paper proposes a regularization framework to incorporate non-standard information not used in ... [more ▼]

Tree based ensemble methods can be seen as a way to learn a kernel from a sample of input-output pairs. This paper proposes a regularization framework to incorporate non-standard information not used in the kernel learning algorithm, so as to take advantage of incomplete information about output values and/or of some prior information about the problem at hand. To this end a generic convex optimization problem is formulated which is first customized into a manifold regularization approach for semi-supervised learning, then as a way to exploit censored output values, and finally as a generic way to exploit prior information about the problem. [less ▲]

Detailed reference viewed: 121 (36 ULg)
Full Text
Peer Reviewed
See detailLarge Margin Classification with the Progressive Hedging Algorithm
Defourny, Boris ULg; Wehenkel, Louis ULg

Conference (2009, December)

Several learning algorithms in classification and structured prediction are formulated as large scale optimization problems. We show that a generic iterative reformulation and resolving strategy based on ... [more ▼]

Several learning algorithms in classification and structured prediction are formulated as large scale optimization problems. We show that a generic iterative reformulation and resolving strategy based on the progressive hedging algorithm from stochastic programming results in a highly parallel algorithm when applied to the large margin classification problem with nonlinear kernels. We also underline promising aspects of the available analysis of progressive hedging strategies. [less ▲]

Detailed reference viewed: 41 (2 ULg)
Full Text
Peer Reviewed
See detailSupervised learning with decision tree-based methods in computational and systems biology
Geurts, Pierre ULg; Irrthum, Alexandre ULg; Wehenkel, Louis ULg

in Molecular Biosystems (2009), 5(12), 1593-1605

At the intersection between artificial intelligence and statistics, supervised learning provides algorithms to automatically build predictive models only from observations of a system. During the last ... [more ▼]

At the intersection between artificial intelligence and statistics, supervised learning provides algorithms to automatically build predictive models only from observations of a system. During the last twenty years, supervised learning has been a tool of choice to analyze the always increasing and complexifying data generated in the context of molecular biology, with successful applications in genome annotation, function prediction, or biomarker discovery. Among supervised learning methods, decision tree-based methods stand out as non parametric methods that have the unique feature of combining interpretability, efficiency, and, when used in ensembles of trees, excellent accuracy. The goal of this paper is to provide an accessible and comprehensive introduction to this class of methods. The first part of the paper is devoted to an intuitive but complete description of decision tree-based methods and a discussion of their strengths and limitations with respect to other supervised learning methods. The second part of the paper provides a survey of their applications in the context of computational and systems biology. The supplementary material provides information about various non-standard extensions of the decision tree-based approach to modeling, some practical guidelines for the choice of parameters and algorithm variants depending on the practical ob jectives of their application, pointers to freely accessible software packages, and a brief primer going through the different manipulations needed to use the tree-induction packages available in the R statistical tool. [less ▲]

Detailed reference viewed: 150 (29 ULg)
Full Text
Peer Reviewed
See detailSecurity Assessment by Multiple Transmission System Operators Exchanging Sensitivity and Tie-Line Power Flow Information
Fabozzi, Davide ULg; Glavic, Mevludin; Wehenkel, Louis ULg et al

in Proceedings of the 2009 IEEE PES Power Tech conference (2009, July)

This paper considers a procedure for multi-area static security assessment of large interconnected power systems operated by a team of Transmission System Operators (TSOs). In this procedure, each TSO ... [more ▼]

This paper considers a procedure for multi-area static security assessment of large interconnected power systems operated by a team of Transmission System Operators (TSOs). In this procedure, each TSO provides the other TSOs with his own equivalent model as well as the detailed effects of contingencies in his control area on all tie-line flows. The paper deals with the implementation of sensitivity-based equivalents suitable for static security assessment. Accuracy with respect to the unreduced model and computational efficiency are considered in evaluating the proposed approach. The relevance of the procedure in the context of recent UCTE operational security policy recommendations is also stressed. The procedure has been implemented in an AC power flow program and tested on a three-area variant of the IEEE 118-bus test system. [less ▲]

Detailed reference viewed: 102 (22 ULg)
Full Text
Peer Reviewed
See detailA new heuristic approach to deal with discrete variables in optimal power flow computations
Capitanescu, Florin ULg; Wehenkel, Louis ULg

in IEEE Power Tech conference (2009, July)

This paper proposes a new heuristic approach to deal with discrete variables in an optimal power flow (OPF). This approach relies on the first order sensitivity of the objective and inequality constraints ... [more ▼]

This paper proposes a new heuristic approach to deal with discrete variables in an optimal power flow (OPF). This approach relies on the first order sensitivity of the objective and inequality constraints with respect to the discrete variables. The impact of a discrete variable change on the objective and inequality constraints is aggregated into a merit function. The proposed approach searches iteratively for better discrete variable settings as long as the problem solution can be improved. We provide numerical results with the proposed approach on four test systems up to 1203 buses and for the OPF problem of active power loss minimization. [less ▲]

Detailed reference viewed: 43 (9 ULg)
Full Text
Peer Reviewed
See detailOptimal power flow computations with constraints limiting the number of control actions
Capitanescu, Florin ULg; Rosehart, William; Wehenkel, Louis ULg

in IEEE Power Tech conference (2009, July)

This paper focuses on optimal power flow (OPF) computations in which no more than a pre-specified number of controls are allowed to move. The benchmark formulation of this OPF problem constitutes a mixed ... [more ▼]

This paper focuses on optimal power flow (OPF) computations in which no more than a pre-specified number of controls are allowed to move. The benchmark formulation of this OPF problem constitutes a mixed integer nonlinear programming (MINLP) problem. To avoid the prohibitive computational time required by classical MINLP approaches to provide a (potentially sub-optimal) solution, we propose instead two alternative approaches. The first one consists in reformulating the MINLP problem as a mathematical program with equilibrium constraints (MPEC). The second approach includes in the classical OPF problem a nonlinear constraint which approximates the integral constraint limiting the number of control variables movement. Both approaches are solved by an interior point algorithm (IPA), slightly adapted to the particular characteristics of each approach. We provide numerical results with the proposed approaches on two test systems and for two practical problems: minimum cost to remove thermal congestion, and minimum cost of load curtailment to restore a feasible equilibrium point. [less ▲]

Detailed reference viewed: 32 (2 ULg)
Full Text
Peer Reviewed
See detailCoupling optimization and dynamic simulation for preventive-corrective control of voltage instability
Capitanescu, Florin ULg; Van Cutsem, Thierry ULg; Wehenkel, Louis ULg

in IEEE Transactions on Power Systems (2009), 24(2), 796-805

This paper proposes an approach coupling security constrained optimal power flow with time-domain simulation to determine an optimal combination of preventive and corrective controls ensuring a voltage ... [more ▼]

This paper proposes an approach coupling security constrained optimal power flow with time-domain simulation to determine an optimal combination of preventive and corrective controls ensuring a voltage stable transition of the system towards a feasible long-term equilibrium, if any of a set of postulated contingencies occurs. A security-constrained optimal power flow is used to adjust the respective contribution of preventive and corrective actions. Furthermore, information is extracted from (quasi steady-state) time-domain simulations to iteratively adjust the set of coupling constraints used by a corrective security constrained optimal power flow until its solution is found dynamically secure and viable. Numerical results are provided on a realistic 55-bus test system. [less ▲]

Detailed reference viewed: 107 (19 ULg)
Full Text
Peer Reviewed
See detailFast Multi-Class Image Annotation with Random Subwindows and Multiple Output Randomized Trees
Dumont, Marie; Marée, Raphaël ULg; Wehenkel, Louis ULg et al

in Proc. International Conference on Computer Vision Theory and Applications (VISAPP) (2009, February)

This paper addresses image annotation, i.e. labelling pixels of an image with a class among a finite set of predefined classes. We propose a new method which extracts a sample of subwindows from a set of ... [more ▼]

This paper addresses image annotation, i.e. labelling pixels of an image with a class among a finite set of predefined classes. We propose a new method which extracts a sample of subwindows from a set of annotated images in order to train a subwindow annotation model by using the extremely randomized trees ensemble method appropriately extended to handle high-dimensional output spaces. The annotation of a pixel of an unseen image is done by aggregating the annotations of its subwindows containing this pixel. The proposed method is compared to a more basic approach predicting the class of a pixel from a single window centered on that pixel and to other state-of-the-art image annotation methods. In terms of accuracy, the proposed method significantly outperforms the basic method and shows good performances with respect to the state-of-the-art, while being more generic, conceptually simpler, and of higher computational efficiency than these latter. [less ▲]

Detailed reference viewed: 112 (19 ULg)
Full Text
Peer Reviewed
See detailContent-based Image Retrieval by Indexing Random Subwindows with Randomized Trees
Marée, Raphaël ULg; Geurts, Pierre ULg; Wehenkel, Louis ULg

in IPSJ Transactions on Computer Vision and Applications (2009), 1

We propose a new method for content-based image retrieval which exploits the similarity measure and indexing structure of totally randomized tree ensembles induced from a set of subwindows randomly ... [more ▼]

We propose a new method for content-based image retrieval which exploits the similarity measure and indexing structure of totally randomized tree ensembles induced from a set of subwindows randomly extracted from a sample of images. We also present the possibility of updating the model as new images come in, and the capability of comparing new images using a model previously constructed from a different set of images. The approach is quantitatively evaluated on various types of images and achieves high recognition rates despite its conceptual simplicity and computational efficiency. [less ▲]

Detailed reference viewed: 135 (25 ULg)
Full Text
Peer Reviewed
See detailInferring bounds on the performance of a control policy from a sample of one-step system transitions
Fonteneau, Raphaël ULg; Murphy, Susan A.; Wehenkel, Louis ULg et al

in 28th Benelux Meeting on Systems and Control (2009)

Detailed reference viewed: 10 (4 ULg)
Full Text
Peer Reviewed
See detailBiomarker discovery in asthma-related inflammation and remodeling.
Quesada Calvo, Florence ULg; Fillet, Marianne ULg; De Seny, Dominique ULg et al

in Proteomics (2009), 9(8), 2163-2170

Asthma is a complex inflammatory disease of airways. A network of reciprocal interactions between inflammatory cells, peptidic mediators, extracellular matrix components, and proteases is thought to be ... [more ▼]

Asthma is a complex inflammatory disease of airways. A network of reciprocal interactions between inflammatory cells, peptidic mediators, extracellular matrix components, and proteases is thought to be involved in the installation and maintenance of asthma-related airway inflammation and remodeling. To date, new proteic mediators displaying significant activity in the pathophysiology of asthma are still to be unveiled. The main objective of this study was to uncover potential target proteins by using surface-enhanced laser desorption/ionization-time of flight-mass spectrometry (SELDI-TOF-MS) on lung samples from mouse models of allergen-induced airway inflammation and remodeling. In this model, we pointed out several protein or peptide peaks that were preferentially expressed in diseased mice as compared to controls. We report the identification of different five proteins: found inflammatory zone 1 or RELM (FIZZ-1), calcyclin (S100A6), clara cell secretory protein 10 (CC10), Ubiquitin, and Histone H4. [less ▲]

Detailed reference viewed: 246 (70 ULg)
Full Text
Peer Reviewed
See detailProtéomique par SELDI-TOF-MS des maladies inflammatoires articulaires: identification des protéines S100 comme protéines d'intérêt
De Seny, Dominique ULg; Ribbens, Clio ULg; Cobraiville, Gaël ULg et al

in Revue Médicale de Liège (2009), 64(Spec No), 29-35

Clinical proteomics is a technical approach studying the entire proteome expressed by cells, tissues or organs. It describes the dynamics of cell regulation by detecting molecular events related to ... [more ▼]

Clinical proteomics is a technical approach studying the entire proteome expressed by cells, tissues or organs. It describes the dynamics of cell regulation by detecting molecular events related to diseases development. Proteomic techniques focus mainly on identification of new biomarkers or new therapeutic targets. It is a multidisciplinary approach using medical, biological, bioanalytical and bioinformatics knowledges. A strong collaboration between these fields allowed SELDI-TOF-MS proteomics studies to be performed at the CHU and the University of Liege, in GIGA-Research facilities. The aim of these studies was driven along three main axes of research related to the identification of biomarkers specific to a studied pathology, to a common biological pathway and, finally, to a treatment response. [less ▲]

Detailed reference viewed: 80 (8 ULg)