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Papers by Hélène Toussaint

Research paper thumbnail of Pipe-lining Dynamic Programming Processes in Order to Synchronize Energy Production and Consumption

Proceedings of the 2020 Federated Conference on Computer Science and Information Systems

Research paper thumbnail of Vehicle driven approaches for non preemptive vehicle relocation with integrated quality criterion in a vehicle sharing system

Annals of Operations Research

Research paper thumbnail of Branch-and-Cut-and-Price algorithms for the preemptive RCPSP

RAIRO - Operations Research

In this article, we address the preemptive Resource-Constrained Precedence Scheduling Problem. We... more In this article, we address the preemptive Resource-Constrained Precedence Scheduling Problem. We propose two mixed integer formulations containing an exponential number of variables and inequalities. An antichain is a set of pairwise incomparable elements with respect to the precedence constraints. In the first formulation, the integer variables are associated with the antichains. For the second, the integer variables are limited to a particular subset of antichains. We propose two Branch-and-Cut-and-Price algorithms for each of these formulations. We introduce some valid inequalities in order to reinforce the second formulation. Finally, we give some computational results on instances of the PSPLIB and compare the formulations.

Research paper thumbnail of Lower and Upper Bounds for the Linear Arrangement Problem on Interval Graphs

RAIRO - Operations Research

We deal here with the Linear Arrangement Problem (LAP) on interval graphs, any interval graph bei... more We deal here with the Linear Arrangement Problem (LAP) on interval graphs, any interval graph being given here together with its representation as the intersection graph of some collection of intervals, and so with related precedence and inclusion relations. We first propose a lower bound LB, which happens to be tight in the case of unit interval graphs. Next, we introduce the restriction PCLAP of LAP which is obtained by requiring any feasible solution of LAP to be consistent with the precedence relation, and prove that PCLAP can be solved in polynomial time. Finally, we show both theoretically and experimentally that PCLAP solutions are a good approximation for LAP on interval graphs.

Research paper thumbnail of Models and Algorithms for Reliability-Oriented Dial-a-Ride with Autonomous Electric Vehicles

European Journal of Operational Research, 2016

Research paper thumbnail of Flow Polyhedra and Resource Constrained Project Scheduling Problems

RAIRO - Operations Research, 2012

This paper aims at describing the way Flow machinery may be used in order to deal with Resource C... more This paper aims at describing the way Flow machinery may be used in order to deal with Resource Constrained Project Scheduling Problems (RCPSP). In order to do it, it first introduces the Timed Flow Polyhedron related to a RCPSP instance. Next it states several structural results related to connectivity and to cut management. It keeps on with a description of the way this framework gives rise to a generic Insertion operator, which enables programmers to design greedy and local search algorithms. It ends with numerical experiments.

Research paper thumbnail of Tree based models and algorithms for the preemptive asymmetric Stacker Crane problem

RAIRO - Operations Research, 2011

In this paper we deal with the preemptive asymmetric stacker crane problem in a heuristic way. We... more In this paper we deal with the preemptive asymmetric stacker crane problem in a heuristic way. We first present some theoretical results which allow us to turn this problem into a specific tree design problem. We next derive from this new representation an integer linear programming model together with simple and efficient greedy and local search heuristics. We conclude by presenting experimental results which aim at both testing the efficiency of our heuristic and evaluating the impact of the preemption hypothesis.

Research paper thumbnail of Une métaheuristique hybride de type GRASP x ELS pour le 3L-CVRP

Research paper thumbnail of Flow Models for Project Scheduling with Transfer Delays and Financial Constraints

Studies in Computational Intelligence, 2013

Research paper thumbnail of Branch and Price for Preemptive and Non Preemptive RCPSP Based on Interval Orders on Precedence Graphs

Studies in Computational Intelligence, 2014

Research paper thumbnail of An effective branch-and-price algorithm for the Preemptive Resource Constrained Project Scheduling Problem based on minimal Interval Order Enumeration

European Journal of Operational Research, 2015

Research paper thumbnail of 2L-CVRP: A GRASP resolution scheme based on RCPSP

2009 International Conference on Computers & Industrial Engineering, 2009

This paper addresses an extension of the well known capacitated vehicle routing problem (CVRP) wh... more This paper addresses an extension of the well known capacitated vehicle routing problem (CVRP) where the customer demands represented by two dimensional weighted items have to be packed into the vehicles. This problem, denoted 2L-CVRP, is NP-hard and it is particularly difficult to solve in practice. We propose a GRASP algorithm in which the loading constraint is handled by a

Research paper thumbnail of Prospective Network Flow Models and Algorithms for Bin Packing Problems

Electronic Notes in Discrete Mathematics, 2010

In this paper, we aim at making appear the way Flow Theory may be used in order to deal with comb... more In this paper, we aim at making appear the way Flow Theory may be used in order to deal with combinatorial geometry problems like the 2D-Bin Packing problem. In order to do it, we state a Reformulation Theorem which associates some flow model with a given Bin-Packing problem, and we provide an algorithm.

Research paper thumbnail of Tree based heuristics for the preemptive asymmetric stacker crane problem

Electronic Notes in Discrete Mathematics, 2010

In this paper, we deal with the preemptive asymmetric stacker crane problem in an heuristic way. ... more In this paper, we deal with the preemptive asymmetric stacker crane problem in an heuristic way. We first turn this problem into a specific tree design problem. We next derive from this new representation simple, efficient greedy and local search heuristics. We conclude by presenting experimental results which aim at both testing the efficiency of our heuristic and at evaluating the impact of the preemption hypothesis.

Research paper thumbnail of A multi-start evolutionary local search for the two-dimensional loading capacitated vehicle routing problem

This paper addresses an extension of the capacitated vehicle routing problem where customer deman... more This paper addresses an extension of the capacitated vehicle routing problem where customer demand is composed of two-dimensional weighted items (2L-CVRP). The objective consists in designing a set of trips minimizing the total transportation cost with a homogenous fleet of vehicles based on a depot node. Items in each vehicle trip must satisfy the two-dimensional orthogonal packing constraints. A GRASP Â ELS algorithm is proposed to compute solutions of a simpler problem in which the loading constraints are transformed into resource constrained project scheduling problem (RCPSP) constraints. We denote this relaxed problem RCPSP-CVRP. The optimization framework deals with RCPSP-CVRP and lastly RCPSP-CVRP solutions are transformed into 2L-CVRP solutions by solving a dedicated packing problem. The effectiveness of our approach is demonstrated through computational experiments including both classical CVRP and 2L-CVRP instances. Numerical experiments show that the GRASP Â ELS approach outperforms all previously published methods.

Research paper thumbnail of Une métaheuristique hybride de type GRASP x ELS pour le 3L-CVRP

Research paper thumbnail of A GRASP x ELS for the vehicle routing problem with three-dimensional loading constraints

ABSTRACT This paper addresses an extension of the capacitated vehicle routing problem where the c... more ABSTRACT This paper addresses an extension of the capacitated vehicle routing problem where the client demand consists of three-dimensional weighted items (3L-CVRP). The objective is to design a set of trips for a homogeneous fleet of vehicles based at a depot node which minimizes the total transportation cost. Items in each vehicle trip must satisfy the three-dimensional orthogonal packing constraints. This problem is strongly connected to real-life transportation systems where the packing of items to be delivered by each vehicle can have a significant impact on the routes. We propose a new way to solve the packing sub-problem. It consists of a two-step procedure in which the z-constraints are first relaxed to get a (x,y) positioning of the items. Then, a compatible z-coordinate is computed to get a packing solution. Items can be rotated but additional constraints such as item fragility, support and LIFO are not considered. This method is included in a GRASP x ELS hybrid algorithm dedicated to the computation of VRP routes. The route optimization alternates between two search spaces: the space of VRP routes and the space of giant trips. The projection from one to the other is done by dedicated procedures (namely the Split and the concatenation algorithms). Moreover, a Local Search is defined on each search space. Furthermore, hash tables are used to store the result of the packing checks and thus save a substantial amount of CPU time. The effectiveness of our approach is illustrated by computational experiments on 3L-CVRP instances from the literature. A new set of realistic instances based on the 96 French districts are also proposed. They range from 19 nodes for the small instances to 255 nodes for the large instances and they can be stated as realistic since they are based on true travel distances in kilometers between French cities. The impact of the hash tables is illustrated as well.

Research paper thumbnail of Lésion pigmentée acquise du pied

Annales de Dermatologie et de Vénéréologie, 2010

Une jeune patiente âgée de 15 ans se présentait à la consultation pour avis concernant une lésion... more Une jeune patiente âgée de 15 ans se présentait à la consultation pour avis concernant une lésion non prurigineuse acquise au cours de la dernière année sur la face interne du pied droit ). À l'examen clinique, il s'agissait d'une macule brune, bien limitée, de 2,5 cm de grand axe, très finement squameuse. Il n'était pas noté d'antécédent médical particulier. Elle avait effectué six et 18 mois auparavant des séjours au Gabon et Sénégal.

Research paper thumbnail of Insertion et Propagation de Contraintes pour le DARP

Les problèmes de Dial/Ride (DARP) concernent le routage et la construction d'horaires des vé... more Les problèmes de Dial/Ride (DARP) concernent le routage et la construction d'horaires des véhicules devant acheminer des charges depuis des nœuds origine vers des nœuds destination à travers un réseau [1]. Les contraintes classiques portent sur la capacité des véhicules et l'existence de fenêtres de temps, les critères à optimiser combinant point de vue économique et qualité de service. Ce problème a aussi vocation à être traité dans un contexte dynamique [1], avec prise en compte de mécanismes de communication usagers ...

Research paper thumbnail of A GRASP× ELS for the vehicle routing problem with basic three-dimensional loading constraints

ABSTRACT This paper addresses an extension of the capacitated vehicle routing problem where the c... more ABSTRACT This paper addresses an extension of the capacitated vehicle routing problem where the client demand consists of three-dimensional weighted items (3L-CVRP). The objective is to design a set of trips for a homogeneous fleet of vehicles based at a depot node which minimizes the total transportation cost. Items in each vehicle trip must satisfy the three-dimensional orthogonal packing constraints. This problem is strongly connected to real-life transportation systems where the packing of items to be delivered by each vehicle can have a significant impact on the routes. We propose a new way to solve the packing sub-problem. It consists of a two-step procedure in which the z-constraints are first relaxed to get a (x,y) positioning of the items. Then, a compatible z-coordinate is computed to get a packing solution. Items can be rotated but additional constraints such as item fragility, support and LIFO are not considered. This method is included in a GRASP x ELS hybrid algorithm dedicated to the computation of VRP routes. The route optimization alternates between two search spaces: the space of VRP routes and the space of giant trips. The projection from one to the other is done by dedicated procedures (namely the Split and the concatenation algorithms). Moreover, a Local Search is defined on each search space. Furthermore, hash tables are used to store the result of the packing checks and thus save a substantial amount of CPU time. The effectiveness of our approach is illustrated by computational experiments on 3L-CVRP instances from the literature. A new set of realistic instances based on the 96 French districts are also proposed. They range from 19 nodes for the small instances to 255 nodes for the large instances and they can be stated as realistic since they are based on true travel distances in kilometers between French cities. The impact of the hash tables is illustrated as well.

Research paper thumbnail of Pipe-lining Dynamic Programming Processes in Order to Synchronize Energy Production and Consumption

Proceedings of the 2020 Federated Conference on Computer Science and Information Systems

Research paper thumbnail of Vehicle driven approaches for non preemptive vehicle relocation with integrated quality criterion in a vehicle sharing system

Annals of Operations Research

Research paper thumbnail of Branch-and-Cut-and-Price algorithms for the preemptive RCPSP

RAIRO - Operations Research

In this article, we address the preemptive Resource-Constrained Precedence Scheduling Problem. We... more In this article, we address the preemptive Resource-Constrained Precedence Scheduling Problem. We propose two mixed integer formulations containing an exponential number of variables and inequalities. An antichain is a set of pairwise incomparable elements with respect to the precedence constraints. In the first formulation, the integer variables are associated with the antichains. For the second, the integer variables are limited to a particular subset of antichains. We propose two Branch-and-Cut-and-Price algorithms for each of these formulations. We introduce some valid inequalities in order to reinforce the second formulation. Finally, we give some computational results on instances of the PSPLIB and compare the formulations.

Research paper thumbnail of Lower and Upper Bounds for the Linear Arrangement Problem on Interval Graphs

RAIRO - Operations Research

We deal here with the Linear Arrangement Problem (LAP) on interval graphs, any interval graph bei... more We deal here with the Linear Arrangement Problem (LAP) on interval graphs, any interval graph being given here together with its representation as the intersection graph of some collection of intervals, and so with related precedence and inclusion relations. We first propose a lower bound LB, which happens to be tight in the case of unit interval graphs. Next, we introduce the restriction PCLAP of LAP which is obtained by requiring any feasible solution of LAP to be consistent with the precedence relation, and prove that PCLAP can be solved in polynomial time. Finally, we show both theoretically and experimentally that PCLAP solutions are a good approximation for LAP on interval graphs.

Research paper thumbnail of Models and Algorithms for Reliability-Oriented Dial-a-Ride with Autonomous Electric Vehicles

European Journal of Operational Research, 2016

Research paper thumbnail of Flow Polyhedra and Resource Constrained Project Scheduling Problems

RAIRO - Operations Research, 2012

This paper aims at describing the way Flow machinery may be used in order to deal with Resource C... more This paper aims at describing the way Flow machinery may be used in order to deal with Resource Constrained Project Scheduling Problems (RCPSP). In order to do it, it first introduces the Timed Flow Polyhedron related to a RCPSP instance. Next it states several structural results related to connectivity and to cut management. It keeps on with a description of the way this framework gives rise to a generic Insertion operator, which enables programmers to design greedy and local search algorithms. It ends with numerical experiments.

Research paper thumbnail of Tree based models and algorithms for the preemptive asymmetric Stacker Crane problem

RAIRO - Operations Research, 2011

In this paper we deal with the preemptive asymmetric stacker crane problem in a heuristic way. We... more In this paper we deal with the preemptive asymmetric stacker crane problem in a heuristic way. We first present some theoretical results which allow us to turn this problem into a specific tree design problem. We next derive from this new representation an integer linear programming model together with simple and efficient greedy and local search heuristics. We conclude by presenting experimental results which aim at both testing the efficiency of our heuristic and evaluating the impact of the preemption hypothesis.

Research paper thumbnail of Une métaheuristique hybride de type GRASP x ELS pour le 3L-CVRP

Research paper thumbnail of Flow Models for Project Scheduling with Transfer Delays and Financial Constraints

Studies in Computational Intelligence, 2013

Research paper thumbnail of Branch and Price for Preemptive and Non Preemptive RCPSP Based on Interval Orders on Precedence Graphs

Studies in Computational Intelligence, 2014

Research paper thumbnail of An effective branch-and-price algorithm for the Preemptive Resource Constrained Project Scheduling Problem based on minimal Interval Order Enumeration

European Journal of Operational Research, 2015

Research paper thumbnail of 2L-CVRP: A GRASP resolution scheme based on RCPSP

2009 International Conference on Computers & Industrial Engineering, 2009

This paper addresses an extension of the well known capacitated vehicle routing problem (CVRP) wh... more This paper addresses an extension of the well known capacitated vehicle routing problem (CVRP) where the customer demands represented by two dimensional weighted items have to be packed into the vehicles. This problem, denoted 2L-CVRP, is NP-hard and it is particularly difficult to solve in practice. We propose a GRASP algorithm in which the loading constraint is handled by a

Research paper thumbnail of Prospective Network Flow Models and Algorithms for Bin Packing Problems

Electronic Notes in Discrete Mathematics, 2010

In this paper, we aim at making appear the way Flow Theory may be used in order to deal with comb... more In this paper, we aim at making appear the way Flow Theory may be used in order to deal with combinatorial geometry problems like the 2D-Bin Packing problem. In order to do it, we state a Reformulation Theorem which associates some flow model with a given Bin-Packing problem, and we provide an algorithm.

Research paper thumbnail of Tree based heuristics for the preemptive asymmetric stacker crane problem

Electronic Notes in Discrete Mathematics, 2010

In this paper, we deal with the preemptive asymmetric stacker crane problem in an heuristic way. ... more In this paper, we deal with the preemptive asymmetric stacker crane problem in an heuristic way. We first turn this problem into a specific tree design problem. We next derive from this new representation simple, efficient greedy and local search heuristics. We conclude by presenting experimental results which aim at both testing the efficiency of our heuristic and at evaluating the impact of the preemption hypothesis.

Research paper thumbnail of A multi-start evolutionary local search for the two-dimensional loading capacitated vehicle routing problem

This paper addresses an extension of the capacitated vehicle routing problem where customer deman... more This paper addresses an extension of the capacitated vehicle routing problem where customer demand is composed of two-dimensional weighted items (2L-CVRP). The objective consists in designing a set of trips minimizing the total transportation cost with a homogenous fleet of vehicles based on a depot node. Items in each vehicle trip must satisfy the two-dimensional orthogonal packing constraints. A GRASP Â ELS algorithm is proposed to compute solutions of a simpler problem in which the loading constraints are transformed into resource constrained project scheduling problem (RCPSP) constraints. We denote this relaxed problem RCPSP-CVRP. The optimization framework deals with RCPSP-CVRP and lastly RCPSP-CVRP solutions are transformed into 2L-CVRP solutions by solving a dedicated packing problem. The effectiveness of our approach is demonstrated through computational experiments including both classical CVRP and 2L-CVRP instances. Numerical experiments show that the GRASP Â ELS approach outperforms all previously published methods.

Research paper thumbnail of Une métaheuristique hybride de type GRASP x ELS pour le 3L-CVRP

Research paper thumbnail of A GRASP x ELS for the vehicle routing problem with three-dimensional loading constraints

ABSTRACT This paper addresses an extension of the capacitated vehicle routing problem where the c... more ABSTRACT This paper addresses an extension of the capacitated vehicle routing problem where the client demand consists of three-dimensional weighted items (3L-CVRP). The objective is to design a set of trips for a homogeneous fleet of vehicles based at a depot node which minimizes the total transportation cost. Items in each vehicle trip must satisfy the three-dimensional orthogonal packing constraints. This problem is strongly connected to real-life transportation systems where the packing of items to be delivered by each vehicle can have a significant impact on the routes. We propose a new way to solve the packing sub-problem. It consists of a two-step procedure in which the z-constraints are first relaxed to get a (x,y) positioning of the items. Then, a compatible z-coordinate is computed to get a packing solution. Items can be rotated but additional constraints such as item fragility, support and LIFO are not considered. This method is included in a GRASP x ELS hybrid algorithm dedicated to the computation of VRP routes. The route optimization alternates between two search spaces: the space of VRP routes and the space of giant trips. The projection from one to the other is done by dedicated procedures (namely the Split and the concatenation algorithms). Moreover, a Local Search is defined on each search space. Furthermore, hash tables are used to store the result of the packing checks and thus save a substantial amount of CPU time. The effectiveness of our approach is illustrated by computational experiments on 3L-CVRP instances from the literature. A new set of realistic instances based on the 96 French districts are also proposed. They range from 19 nodes for the small instances to 255 nodes for the large instances and they can be stated as realistic since they are based on true travel distances in kilometers between French cities. The impact of the hash tables is illustrated as well.

Research paper thumbnail of Lésion pigmentée acquise du pied

Annales de Dermatologie et de Vénéréologie, 2010

Une jeune patiente âgée de 15 ans se présentait à la consultation pour avis concernant une lésion... more Une jeune patiente âgée de 15 ans se présentait à la consultation pour avis concernant une lésion non prurigineuse acquise au cours de la dernière année sur la face interne du pied droit ). À l'examen clinique, il s'agissait d'une macule brune, bien limitée, de 2,5 cm de grand axe, très finement squameuse. Il n'était pas noté d'antécédent médical particulier. Elle avait effectué six et 18 mois auparavant des séjours au Gabon et Sénégal.

Research paper thumbnail of Insertion et Propagation de Contraintes pour le DARP

Les problèmes de Dial/Ride (DARP) concernent le routage et la construction d'horaires des vé... more Les problèmes de Dial/Ride (DARP) concernent le routage et la construction d'horaires des véhicules devant acheminer des charges depuis des nœuds origine vers des nœuds destination à travers un réseau [1]. Les contraintes classiques portent sur la capacité des véhicules et l'existence de fenêtres de temps, les critères à optimiser combinant point de vue économique et qualité de service. Ce problème a aussi vocation à être traité dans un contexte dynamique [1], avec prise en compte de mécanismes de communication usagers ...

Research paper thumbnail of A GRASP× ELS for the vehicle routing problem with basic three-dimensional loading constraints

ABSTRACT This paper addresses an extension of the capacitated vehicle routing problem where the c... more ABSTRACT This paper addresses an extension of the capacitated vehicle routing problem where the client demand consists of three-dimensional weighted items (3L-CVRP). The objective is to design a set of trips for a homogeneous fleet of vehicles based at a depot node which minimizes the total transportation cost. Items in each vehicle trip must satisfy the three-dimensional orthogonal packing constraints. This problem is strongly connected to real-life transportation systems where the packing of items to be delivered by each vehicle can have a significant impact on the routes. We propose a new way to solve the packing sub-problem. It consists of a two-step procedure in which the z-constraints are first relaxed to get a (x,y) positioning of the items. Then, a compatible z-coordinate is computed to get a packing solution. Items can be rotated but additional constraints such as item fragility, support and LIFO are not considered. This method is included in a GRASP x ELS hybrid algorithm dedicated to the computation of VRP routes. The route optimization alternates between two search spaces: the space of VRP routes and the space of giant trips. The projection from one to the other is done by dedicated procedures (namely the Split and the concatenation algorithms). Moreover, a Local Search is defined on each search space. Furthermore, hash tables are used to store the result of the packing checks and thus save a substantial amount of CPU time. The effectiveness of our approach is illustrated by computational experiments on 3L-CVRP instances from the literature. A new set of realistic instances based on the 96 French districts are also proposed. They range from 19 nodes for the small instances to 255 nodes for the large instances and they can be stated as realistic since they are based on true travel distances in kilometers between French cities. The impact of the hash tables is illustrated as well.