References of "Louveaux, Quentin"
     in
Bookmark and Share    
Full Text
Peer Reviewed
See detailOptimization Tool for the Strategic Outline and Sizing of District Heating Networks Using a Geographic Information System
Resimont, Thibaut ULiege; Louveaux, Quentin ULiege; Dewallef, Pierre ULiege

in Energies (2021), 14(17), 5575

The implementation of district heating networks into cities is a main topic in policy planning that looks for sustainable solutions to reduce CO2 emissions. However, their development into cities is ... [more ▼]

The implementation of district heating networks into cities is a main topic in policy planning that looks for sustainable solutions to reduce CO2 emissions. However, their development into cities is generally limited by a high initial investment cost. The development of optimization methods intended to draft efficient systems using heating consumption profiles into a prescribed geo-graphic area are useful in this purpose. Such tools are already referred to in the scientific litera-ture, yet they are often restricted to limit the computational load. To bridge this gap, the present contribution proposes a multi-period mixed integer linear programming model for the optimal outline and sizing of a district heating network maximizing the net cash flow based on a geo-graphic information system. This methodology targets a large range of problem sizes from small-scale to large-scale heating networks while guaranteeing numerical robustness. For sake of simplicity, the developed model is first applied to a scaled down case study with 3 available heating sources and a neighborhood of 16 streets. The full-scale model is presented afterwards to demonstrate the applicability of the tool for city-scale heating networks with around 2000 streets to potentially connect within a reasonable computational time of around only one hour. [less ▲]

Detailed reference viewed: 67 (9 ULiège)
Full Text
Peer Reviewed
See detailSiting Renewable Power Generation Assets with Combinatorial Optimisation
Berger, Mathias ULiege; Radu, David-Constantin ULiege; Dubois, Antoine ULiege et al

in Optimization Letters (2021)

This paper studies the problem of siting renewable power generation assets using large amounts of climatological data while accounting for their spatiotemporal complementarity. The problem is cast as a ... [more ▼]

This paper studies the problem of siting renewable power generation assets using large amounts of climatological data while accounting for their spatiotemporal complementarity. The problem is cast as a combinatorial optimisation problem selecting a pre-specified number of sites so as to minimise the number of simultaneous low electricity production events that they experience relative to a pre-specified reference production level. It is shown that the resulting model is closely related to submodular optimisation and can be interpreted as generalising the well-known maximum coverage problem. Both deterministic and randomised algorithms are discussed, including greedy, local search and relaxation-based heuristics as well as combinations of these algorithms. The usefulness of the model and methods is illustrated by a realistic case study inspired by the problem of siting onshore wind power plants in Europe, resulting in instances featuring over ten thousand candidate locations and ten years of hourly-sampled meteorological data. The proposed solution methods are benchmarked against a state-of-the-art mixed-integer programming solver and several algorithms are found to consistently produce better solutions at a fraction of the computational cost. The physical nature of solutions provided by the model is also investigated, and all deployment patterns are found to be unable to supply a constant share of the electricity demand at all times. Finally, a cross-validation analysis shows that, except for an edge case, the model can successfully and reliably identify deployment patterns that perform well on previously unseen climatological data from historical data spanning a small number of weather years. [less ▲]

Detailed reference viewed: 445 (80 ULiège)
Full Text
Peer Reviewed
See detailAssessing the Impact of Offshore Wind Siting Strategies on the Design of the European Power System
Radu, David-Constantin ULiege; Berger, Mathias ULiege; Dubois, Antoine ULiege et al

in Applied Energy (2021), 305

This paper provides a detailed account of the impact of different offshore wind siting strategies on the design of the European power system. To this end, a two-stage method is proposed. In the first ... [more ▼]

This paper provides a detailed account of the impact of different offshore wind siting strategies on the design of the European power system. To this end, a two-stage method is proposed. In the first stage, a highly-granular siting problem identifies a suitable set of sites where offshore wind plants could be deployed according to a pre-specified criterion. Two siting schemes are analysed and compared within a realistic case study. These schemes essentially select a pre-specified number of sites so as to maximize their aggregate power output and their spatiotemporal complementarity, respectively. In addition, two variants of these siting schemes are provided, wherein the number of sites to be selected is specified on a country-by-country basis rather than Europe-wide. In the second stage, the subset of previously-identified sites is passed to a capacity expansion planning framework that sizes the power generation, transmission and storage assets that should be deployed and operated in order to satisfy pre-specified electricity demand levels at minimum cost. Results show that the complementarity-based siting criterion leads to system designs which are up to 5% cheaper than the ones relying on the power output-based scheme when offshore wind plants are deployed with no consideration for country-based deployment targets. On the contrary, the power output-based scheme leads to system designs which are consistently 2% cheaper than the ones leveraging the complementarity-based siting strategy when such constraints are enforced. The robustness of the reported results is supported by a sensitivity analysis on offshore wind capital expenditure and inter-annual weather variability, respectively. [less ▲]

Detailed reference viewed: 1039 (48 ULiège)
Full Text
Peer Reviewed
See detailSupervised learning of convex piecewise linear approximations of optimization problems
Duchesne, Laurine ULiege; Louveaux, Quentin ULiege; Wehenkel, Louis ULiege

in Proceedings of the 29th European Symposium on Artificial Neural Networks, Computational Intelligence and Machine Learning (2021)

We propose to use input convex neural networks (ICNN) to build convex approximations of non-convex feasible sets of optimization problems, in the form of a set of linear equalities and inequalities in a ... [more ▼]

We propose to use input convex neural networks (ICNN) to build convex approximations of non-convex feasible sets of optimization problems, in the form of a set of linear equalities and inequalities in a lifted space. Our approach may be tailored to yield both inner- and outer- approximations, or to maximize its accuracy in regions closer to the minimum of a given objective function. We illustrate the method on two-dimensional toy problems and motivate it by various instances of reliability management problems of large-scale electric power systems. [less ▲]

Detailed reference viewed: 85 (2 ULiège)
Full Text
Peer Reviewed
See detailOn the length of monotone paths in polyhedra
Blanchard, Moise; De Loera, Jesus; Louveaux, Quentin ULiege

in SIAM Journal on Discrete Mathematics (2021)

Motivated by the problem of bounding the number of iterations of the Simplex algorithm we investigate the possible lengths of monotone paths followed inside the oriented graphs of polyhedra (oriented by ... [more ▼]

Motivated by the problem of bounding the number of iterations of the Simplex algorithm we investigate the possible lengths of monotone paths followed inside the oriented graphs of polyhedra (oriented by the objective function). We consider both the shortest and the longest monotone paths and estimate the monotone diameter and height of polyhedra. Our analysis applies to transportation polytopes, matroid polytopes, matching polytopes, shortest-path polytopes, and the TSP, among others. We begin by showing that combinatorial cubes have monotone diameter and Bland simplex height upper bounded by their dimension and that in fact all monotone paths of zonotopes are no larger than the number of edge directions of the zonotope. We later use this to show that several polytopes have polynomial-size monotone diameter. In contrast, we show that for many well-known combinatorial polytopes, the height is at least exponential. Surprisingly, for some famous pivot rules, e.g., greatest improvement and steepest edge, these same polytopes have polynomial-size simplex paths. [less ▲]

Detailed reference viewed: 36 (11 ULiège)
Full Text
Peer Reviewed
See detailClustering and Kernel Density Estimation for Assessment of Measurable Residual Disease by Flow Cytometry
Jacqmin, Hugues; Chatelain, Bernard; Louveaux, Quentin ULiege et al

in Diagnostics (2020), 10(5),

Standardization, data mining techniques, and comparison to normality are changing the landscape of multiparameter flow cytometry in clinical hematology. On the basis of these principles, a strategy was ... [more ▼]

Standardization, data mining techniques, and comparison to normality are changing the landscape of multiparameter flow cytometry in clinical hematology. On the basis of these principles, a strategy was developed for measurable residual disease (MRD) assessment. Herein, suspicious cell clusters are first identified at diagnosis using a clustering algorithm. Subsequently, automated multidimensional spaces, named “Clouds”, are created around these clusters on the basis of density calculations. This step identifies the immunophenotypic pattern of the suspicious cell clusters. Thereafter, using reference samples, the “Abnormality Ratio” (AR) of each Cloud is calculated, and major malignant Clouds are retained, known as “Leukemic Clouds” (L-Clouds). In follow-up samples, MRD is identified when more cells fall into a patient’s L-Cloud compared to reference samples (AR concept). This workflow was applied on simulated data and real-life leukemia flow cytometry data. On simulated data, strong patient-dependent positive correlation (R2 = 1) was observed between the AR and spiked-in leukemia cells. On real patient data, AR kinetics was in line with the clinical evolution for five out of six patients. In conclusion, we present a convenient flow cytometry data analysis approach for the follow-up of hematological malignancies. Further evaluation and validation on more patient samples and different flow cytometry panels is required before implementation in clinical practice. [less ▲]

Detailed reference viewed: 44 (5 ULiège)
Full Text
See detailOperation rules of the Vesdre reservoir revisited
Dewals, Benjamin ULiege; Cuvelier, Thibaut; Archambeau, Pierre ULiege et al

Conference (2019, September 13)

Detailed reference viewed: 74 (7 ULiège)
Full Text
Peer Reviewed
See detailComparison Between Robust and Stochastic Optimisation for Long-term Reservoir Management Under Uncertainty
Cuvelier, Thibaut ULiege; Archambeau, Pierre ULiege; Dewals, Benjamin ULiege et al

in Water Resources Management (2018), 32(5), 15991614

Long-term reservoir management often uses bounds on the reservoir level, between which the operator can work. However, these bounds are not always kept up-to-date with the latest knowledge about the ... [more ▼]

Long-term reservoir management often uses bounds on the reservoir level, between which the operator can work. However, these bounds are not always kept up-to-date with the latest knowledge about the reservoir drainage area, and thus become obsolete. The main difficulty with bounds computation is to correctly take into account the high uncertainty about the inflows to the reservoir. In this article, we propose a methodology to derive minimum bounds while providing formal guarantees about the quality of the obtained solutions. The uncertainty is embedded using either stochastic or robust programming in a model-predictive-control framework. We compare the two paradigms to the existing solution for a case study and find that the obtained solutions vary substantially. By combining the stochastic and the robust approaches, we also assign a confidence level to the solutions obtained by stochastic programming. The proposed methodology is found to be both efficient and easy to implement. It relies on sound mathematical principles, ensuring that a global optimum is reached in all cases. [less ▲]

Detailed reference viewed: 110 (26 ULiège)
Full Text
Peer Reviewed
See detailOptimising workforce and energy costs by exploiting production flexibility
Cuvelier, Thibaut ULiege; Louveaux, Quentin ULiege

Conference (2017, July)

In a world where the electricity prices become more and more volatile, notably due to renewable energies, the industry is suffering from cost variations never seen before, especially when electro ... [more ▼]

In a world where the electricity prices become more and more volatile, notably due to renewable energies, the industry is suffering from cost variations never seen before, especially when electro-intensive. Nevertheless, the plants can significantly reduce this impact: some electro-intensive factories could shift their production to time periods where the electricity is cheaper, resulting in large savings. At the same time, the grid operator can remunerate this consumption adaptation as a flexibility service. Our research goal is to optimise the operations of a factory around this flexibility. We compute a production plan that adapts to price forecasts, but also flexibility levers that adjust this plan to react to unexpected price changes. We propose the unifying concept of reservoir to provide sufficiently good models for the plant's processes. Nevertheless, this methodology implies to have frequent production plan changes, which directly impacts the workers, as they may be asked to follow barely predictable schedules. This has a significant detrimental effect on their quality of life. As a consequence, the human aspect of flexibility must also be considered: we seek for production plans that consider both workforce and energy costs, and we then assign workers to work shifts while ensuring their well-being. This HR orientation is the most innovative contribution of this research project. [less ▲]

Detailed reference viewed: 150 (22 ULiège)
Full Text
Peer Reviewed
See detailA Machine Learning-Based Approximation of Strong Branching
Marcos Alvarez, Alejandro ULiege; Louveaux, Quentin ULiege; Wehenkel, Louis ULiege

in INFORMS Journal on Computing (2017), 29(1), 185-195

We present in this paper a new generic approach to variable branching in branch-and-bound for mixed- integer linear problems. Our approach consists in imitating the decisions taken by a good branching ... [more ▼]

We present in this paper a new generic approach to variable branching in branch-and-bound for mixed- integer linear problems. Our approach consists in imitating the decisions taken by a good branching strategy, namely strong branching, with a fast approximation. This approximated function is created by a machine learning technique from a set of observed branching decisions taken by strong branching. The philosophy of the approach is similar to reliability branching. However, our approach can catch more complex aspects of observed previous branchings in order to take a branching decision. The experiments performed on randomly generated and MIPLIB problems show promising results. [less ▲]

Detailed reference viewed: 372 (20 ULiège)
Full Text
Peer Reviewed
See detailA Quantitative Doignon-Bell-Scarf theorem
Aliev, Iskander; Bassett, Robert; De Loera, Jesus et al

in Combinatorica (2017)

The famous Doignon-Bell-Scarf theorem is a Helly-type result about the existence of integer solutions to systems of linear inequalities. The purpose of this paper is to present the following quantitative ... [more ▼]

The famous Doignon-Bell-Scarf theorem is a Helly-type result about the existence of integer solutions to systems of linear inequalities. The purpose of this paper is to present the following quantitative generalization: Given an integer k, we prove that there exists a constant c(n,k), depending only on the dimension n and on the number k, such that if a bounded polyhedron {x in R^n : Ax <= b} contains exactly k integer points, then there exists a subset of the rows, of cardinality no more than c(n,k), defining a polyhedron that contains exactly the same k integer points. In this case c(n,0)=2^n as in the original case of Doignon-Bell-Scarf for infeasible systems of inequalities. We work on both upper and lower bounds for the constant c(n,k) and discuss some consequences, including a Clarkson-style algorithm to find the l-th best solution of an integer program with respect to the ordering induced by the objective function. [less ▲]

Detailed reference viewed: 98 (14 ULiège)
Full Text
Peer Reviewed
See detailGuided Dive for the Spatial Branch-and-Bound
Gerard, Damien ULiege; Koeppe, Matthias; Louveaux, Quentin ULiege

in Journal of Global Optimization (2017)

We study the spatial Brand-and-Bound algorithm for the global opti- mization of nonlinear problems. In particular we are interested in a method to find quickly good feasible solutions. Most spatial Branch ... [more ▼]

We study the spatial Brand-and-Bound algorithm for the global opti- mization of nonlinear problems. In particular we are interested in a method to find quickly good feasible solutions. Most spatial Branch-and-Bound-based solvers use a non-global solver at a few nodes to try to find better incumbents. We show that it is possible to improve the branching rules and the node priority by exploiting the solutions from the non-global solver. We also propose several smart adaptive strategies to choose when to run the non-global solver. We show that despite the time spent in solving more NLP problems in the nodes, the new strategies enable the algorithm to find the first good incumbents faster and to prove the global opti- mality faster. Numerous easy, medium size as well as hard NLP instances from the Coconut library are benchmarked. All experiments are run using the open source solver Couenne. [less ▲]

Detailed reference viewed: 69 (15 ULiège)
Full Text
Peer Reviewed
See detailDirect control service from residential heat pump aggregation with specified payback
Georges, Emeline ULiege; Cornélusse, Bertrand ULiege; Ernst, Damien ULiege et al

in Proceedings of the 19th Power Systems Computation Conference (PSCC) (2016, June)

This paper addresses the problem of an aggregator controlling residential heat pumps to offer a direct control flexibility service. The service is defined by a 15 minute power modulation, upward or ... [more ▼]

This paper addresses the problem of an aggregator controlling residential heat pumps to offer a direct control flexibility service. The service is defined by a 15 minute power modulation, upward or downward, followed by a payback of one hour and 15 minutes. The service modulation is relative to an optimized baseline that minimizes the energy costs. The potential amount of modulable power and the payback effect are computed by solving mixed integer linear problems. Within these problems, the building thermal behavior is modeled by an equivalent thermal network made of resistances and lumped capacitances whose parameters are identified from validated models. Simulations are performed on 100 freestanding houses. For an average 4.3 kW heat pump, results show a potential of 1.2 kW upward modulation with a payback of 600 Wh and 150 Wh of overconsumption. A downward modulation of 500 W per house can be achieved with a payback of 420 Wh and 120 Wh of overconsumption. [less ▲]

Detailed reference viewed: 234 (39 ULiège)
Full Text
Peer Reviewed
See detailParametric Polyhedra with at least k Lattice Points: Their Semigroup Structure and the k-Frobenius Problem
Aliev, Iskander; De Loera, Jesus; Louveaux, Quentin ULiege

in Beveridge, Andrew; Griggs, Jerold; Hogben, Leslie (Eds.) et al Recent trends in Combinatorics (2016)

The well-studied semigroup Sg(A) = {b : b = Ax; x in Z^n; x >= 0} can be stratified by the sizes of the polyhedral fibers IPA(b) = {x : Ax = b; x >= 0; x in Z^n}. The key theme of this paper is a ... [more ▼]

The well-studied semigroup Sg(A) = {b : b = Ax; x in Z^n; x >= 0} can be stratified by the sizes of the polyhedral fibers IPA(b) = {x : Ax = b; x >= 0; x in Z^n}. The key theme of this paper is a structure theory that characterizes precisely the set Sg_k(A) of all vectors b in Sg(A) such that their fiber IPA(b) has at least k-solutions. We demonstrate that this set is finitely generated, a union of translated copies of a semigroup which can be computed explicitly via Hilbert bases computations. Related results can be derived for those right-hand-side vectors b for which IPA(b) has exactly k solutions or fewer than k solutions. We also show that, when n, k are fixed natural numbers, one can compute in polynomial time an encoding of Sg_k(A) as a generating function, using a short sum of rational functions. As a consequence, one can identify all right-hand-side vectors that have at least k solutions. Using this tool we prove that for fixed n; k the k-Frobenius number can be computed in polynomial time, generalizing a well-known result of R. Kannan. [less ▲]

Detailed reference viewed: 67 (9 ULiège)
Full Text
Peer Reviewed
See detailBox search for the data mining of the key parameters of an industrial process
Louveaux, Quentin ULiege; Mathei, Axel; Mathieu, Sébastien ULiege

in Intelligent Data Analysis (2016), 20(6),

To increase their competitiveness, many industrial companies monitor their production process, collecting large amount of measurements. This paper describes a technique using this data to improve the ... [more ▼]

To increase their competitiveness, many industrial companies monitor their production process, collecting large amount of measurements. This paper describes a technique using this data to improve the performance of a monitored process. In particular we wish to find a set of rules, i.e. intervals on a reduced number of parameters, for which an output value is maximized. The model-free optimization problem to solve is to find a box, restricted on a limited amount of dimensions, with the maximum mean value of the included points. This article compares a machine learning-based heuristic to the solution computed by a mixed-integer linear program on real-life databases from steel and glass manufacturing. Computational results show that the heuristic obtains comparable solutions to the mixed integer linear approach. However, the exact approach is computationally too expensive to tackle real life databases. Results show that the restriction of five process parameters, on these databases, may improve the quality of the process by 50%. [less ▲]

Detailed reference viewed: 60 (9 ULiège)
Full Text
See detailFeasibility-oriented Branching Strategies for Global Optimization
Gerard, Damien ULiege; Köppe, Matthias; Louveaux, Quentin ULiege

E-print/Working paper (2016)

We study the spatial Brand-and-Bound algorithm for the global optimization of nonlinear problems. In particular we are interested in a method to find quickly good feasible solutions. Most spatial Branch ... [more ▼]

We study the spatial Brand-and-Bound algorithm for the global optimization of nonlinear problems. In particular we are interested in a method to find quickly good feasible solutions. Most spatial Branch-and-Bound-based solvers use a non global solver at a few nodes to try to find better incumbents. We show that it is possible to improve the branching rules and the node priority by exploiting the solutions from the non global solver. We also propose several smart adaptive strategies to choose when to run the non global solver. We show that despite the time spent in solving many more NLP problems in the nodes, the new strategies enable the algorithm to find the first good incumbents faster and to prove the global optimality faster. Numerous easy, medium size as well as hard NLP instances from the Coconut library are benchmarked. All experiments are run using the open source solver Couenne. [less ▲]

Detailed reference viewed: 68 (11 ULiège)
Full Text
See detailInteger Programming and Combinatorial Optimization
Louveaux, Quentin ULiege; Skutella, Martin

Book published by Springer (2016)

Detailed reference viewed: 56 (9 ULiège)
Full Text
See detailOnline Learning for Strong Branching Approximation in Branch-and-Bound
Marcos Alvarez, Alejandro ULiege; Wehenkel, Louis ULiege; Louveaux, Quentin ULiege

E-print/Working paper (2016)

We present an online learning approach to variable branching in branch-and-bound for mixed-integer linear problems. Our approach consists in learning strong branching scores in an online fashion and in ... [more ▼]

We present an online learning approach to variable branching in branch-and-bound for mixed-integer linear problems. Our approach consists in learning strong branching scores in an online fashion and in using them to take branching decisions. More specifically, numerical scores are used to rank the branching candidates. If, for a given variable, the learned approximation is deemed reliable, then the score for that variable is computed thanks to the learned function. If the approximation is not reliable yet, the real strong branching score is used instead. The scores that are computed through the real strong branching procedure are fed to the online learning algorithm in order to improve the approximated function. The experiments show promising results. [less ▲]

Detailed reference viewed: 371 (10 ULiège)
Full Text
Peer Reviewed
See detailDSIMA: A testbed for the quantitative analysis of interaction models within distribution networks
Mathieu, Sébastien ULiege; Louveaux, Quentin ULiege; Ernst, Damien ULiege et al

in Sustainable Energy, Grids and Networks (2016), 5

This article proposes an open-source testbed to simulate interaction models governing the exchange of flexibility services located within a distribution network. The testbed is an agent-based system in ... [more ▼]

This article proposes an open-source testbed to simulate interaction models governing the exchange of flexibility services located within a distribution network. The testbed is an agent-based system in which the distribution system operator, the transmission system operator, producers and retailers make their decisions based on mixed-integer linear programs. This testbed helps to highlight the characteristics of an interaction model, the benefits for the agents and eases the detection of unwanted or abusive behaviors which decreases the welfare. The testbed is implemented in Python and the optimization problems are encoded in the modeling language ZIMPL. A web interface is coupled with an instance generator using macroscopic parameters of the system such as the total power production. This testbed is, therefore, well suited to test the implemented interaction models on various scenarios and to extend the implementation to other models. Five interaction models developed with industrial partners are simulated over a year on a 75-bus test system. Simulations show that interaction models relying on active network management, as they have been developed, lead to substantial welfare even though they suffer from a lack of coordination between the DSO and the TSO. A conservative interaction model restricting grid users to an access range that is computed ahead of time to prevent any congestion, avoids shedding distributed generation but considerably restrains the amount of distributed production. [less ▲]

Detailed reference viewed: 696 (64 ULiège)