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Papers by Abdallah Elkhyari

HAL (Le Centre pour la Communication Scientifique Directe), Feb 26, 2003

HAL (Le Centre pour la Communication Scientifique Directe), Sep 8, 2002

China Medical Herald, 2011

With the rapid development of medical imaging technology and the advanced understanding of Parkin... more With the rapid development of medical imaging technology and the advanced understanding of Parkinson ′s dis-ease(PD) from the view of functional imaging,the functional imaging techniques represented by single photon emission to-mography/CT(SPECT/CT),positron emission tomography/CT(PET/CT) and magnetic resonance spectroscopy(MRS),can show changes of cerebral blood flow,metabolism,neurotransmitter,transporter and receptor,having some advantages in early diagnosis of PD.

Scheduling problems considered in the literature are often static (activities are known in advanc... more Scheduling problems considered in the literature are often static (activities are known in advance and constraints are fixed). However, every real-life schedule is subject to unexpected events. In these cases, a new solution is needed in a preferably short time and as close as possible to the current solution. In this paper, we present an exact approach for solving dynamic Resource-Constrained Project Scheduling Problems or RCPSP. This approach combines explanation-based constraint programming and operational research techniques. We present our first experimental results that show impressive improvements in both computation time and stability when comparing our approach to a re-execution from scratch.

Scheduling problems have been studied a lot over the last decade. Due to the complexity and the v... more Scheduling problems have been studied a lot over the last decade. Due to the complexity and the variety of such problems, most works consider static problems in which activities are known in advance and constraints are fixed. However, every scheduling problem is subject to unexpected events (consider for example a new activity to schedule, or a machine breakdown). In these cases, a new solution is needed in a preferably short time taking these events into account and as close as possible to the current solution. In this paper, we present an exact approach for solving dynamic scheduling problems. This approach uses explanation-based constraint programming and operational research techniques. Our tools have been designed for a general scheduling problem: the Resource-Constrained Project Scheduling Problem (RCPSP).

Les problemes d'ordonnancement constituent une classe importante des problemes d'optimisa... more Les problemes d'ordonnancement constituent une classe importante des problemes d'optimisation combinatoire. La plupart des travaux dans ce domaine considerent des problemes statiques pour lesquels toutes les donnees (activites, ressources, contraintes) sont connues a l'avance. En realite, ce type de problemes est tres souvent soumis aux aleas (matieres premieres livrees en retard, arrivees de nouvelles commandes, pannes de machines, etc.). Aussi, l'ordonnancement se deroule rarement comme prevu. On a alors affaire a un probleme d'ordonnancement dit dynamique. Dans cette these, nous considerons un probleme d'ordonnancement tres general, appele RCPSP (Resource Constrained Project Scheduling Problem), et proposons un systeme permettant de resoudre le cas dynamique. Bien que beaucoup de travaux concernent le RCPSP statique, seules quelques methodes sont proposees pour le cas dynamique. De plus ces methodes ne sont pas satisfaisantes. La methode que nous proposons...

The Resource Constrained Project Scheduling Problem (rcpsp) is a general scheduling problem which... more The Resource Constrained Project Scheduling Problem (rcpsp) is a general scheduling problem which consists in scheduling a set of activities taking into account temporal and resource constraints (Demeulemeester and Herroelen, 2002). Preemption is not allowed. The objective considered here is the minimization of the makespan (total duration) of the project. This problem is NP-hard (Blazewicz et al., 1983). Most work about rcpsp consider static problems in which activities are known in advance and constraints are fixed. However, every schedule is subject to unexpected events (consider for example a new activity to schedule, or a resource failure – eg. machine breakdown). When such a situation arises, a new solution taking these events into account is needed generally in a short time. Furthermore, this new solution must preferably be not too far from the previous one. Several works concern dynamic scheduling problems. But generally, they deal with very specific problems like one-machin...

The Resource Constrained Project Scheduling Problem (rcpsp) is a general scheduling problem. It c... more The Resource Constrained Project Scheduling Problem (rcpsp) is a general scheduling problem. It consists of a set of activities and a set of renewable resources. Each resource is available in a given constant amount. Each activity has a duration and requires a constant amount of resource to be processed. Preemption is not allowed. Activities are related by two sets of constraints: temporal constraints modelled through precedence constraints, and resource constraints that state that for each time period and for each resource, the total demand cannot exceed the resource capacity. The objective considered here is the minimization of the makespan (total duration) of the project. This problem is NP-hard [3]. Most work about rcpsp consider static problems in which activities are known in advance and constraints are fixed. However, every schedule is subject to unexpected events (consider for example a new activity to schedule, or a resource failure – eg. machine breakdown). When such a sit...

Scheduling problems considered in the literature are often static (activities are known in advanc... more Scheduling problems considered in the literature are often static (activities are known in advance and constraints are fixed). However, every real-life schedule is subject to unexpected events. In these cases, a new solution is needed in a preferably short time and as close as possible to the current solution. In this paper, we present an exact approach for solving dynamic Resource-Constrained Project Scheduling Problems or RCPSP. This approach combines explanation-based constraint programming and operational research techniques. We present our first experimental results that show impressive improvements in both computation time and stability when comparing our approach to a re-execution from scratch.

This paper introduces a new method based on constraint programming (CP) and genetic algorithm (GA... more This paper introduces a new method based on constraint programming (CP) and genetic algorithm (GA) for solving dynamic scheduling problems. The proposed approach allows us to handle scheduling problems with large sizes (i.e. search spaces are too large). Our idea is to break up the search space into disjoined sub-spaces by the genetic algorithm. To each individual of the population is associated a sub-space. Each sub-space is represented by a sub-CSP which is easier to solve than the original scheduling problem. Our first experimentations are addressed to the Endoscopy Unit scheduling in dynamic way.

Publikationsansicht. 44868480. Utilisation de la programmation par contraintes pour le problème ... more Publikationsansicht. 44868480. Utilisation de la programmation par contraintes pour le problème d'allocation de fréquences en téléphonie cellulaire / (2002). Ducharme, Alain. Abstract. "Mémoire présenté en vue de l'obtention ...

HAL (Le Centre pour la Communication Scientifique Directe), Feb 26, 2003

HAL (Le Centre pour la Communication Scientifique Directe), Sep 8, 2002

China Medical Herald, 2011

With the rapid development of medical imaging technology and the advanced understanding of Parkin... more With the rapid development of medical imaging technology and the advanced understanding of Parkinson ′s dis-ease(PD) from the view of functional imaging,the functional imaging techniques represented by single photon emission to-mography/CT(SPECT/CT),positron emission tomography/CT(PET/CT) and magnetic resonance spectroscopy(MRS),can show changes of cerebral blood flow,metabolism,neurotransmitter,transporter and receptor,having some advantages in early diagnosis of PD.

Scheduling problems considered in the literature are often static (activities are known in advanc... more Scheduling problems considered in the literature are often static (activities are known in advance and constraints are fixed). However, every real-life schedule is subject to unexpected events. In these cases, a new solution is needed in a preferably short time and as close as possible to the current solution. In this paper, we present an exact approach for solving dynamic Resource-Constrained Project Scheduling Problems or RCPSP. This approach combines explanation-based constraint programming and operational research techniques. We present our first experimental results that show impressive improvements in both computation time and stability when comparing our approach to a re-execution from scratch.

Scheduling problems have been studied a lot over the last decade. Due to the complexity and the v... more Scheduling problems have been studied a lot over the last decade. Due to the complexity and the variety of such problems, most works consider static problems in which activities are known in advance and constraints are fixed. However, every scheduling problem is subject to unexpected events (consider for example a new activity to schedule, or a machine breakdown). In these cases, a new solution is needed in a preferably short time taking these events into account and as close as possible to the current solution. In this paper, we present an exact approach for solving dynamic scheduling problems. This approach uses explanation-based constraint programming and operational research techniques. Our tools have been designed for a general scheduling problem: the Resource-Constrained Project Scheduling Problem (RCPSP).

Les problemes d'ordonnancement constituent une classe importante des problemes d'optimisa... more Les problemes d'ordonnancement constituent une classe importante des problemes d'optimisation combinatoire. La plupart des travaux dans ce domaine considerent des problemes statiques pour lesquels toutes les donnees (activites, ressources, contraintes) sont connues a l'avance. En realite, ce type de problemes est tres souvent soumis aux aleas (matieres premieres livrees en retard, arrivees de nouvelles commandes, pannes de machines, etc.). Aussi, l'ordonnancement se deroule rarement comme prevu. On a alors affaire a un probleme d'ordonnancement dit dynamique. Dans cette these, nous considerons un probleme d'ordonnancement tres general, appele RCPSP (Resource Constrained Project Scheduling Problem), et proposons un systeme permettant de resoudre le cas dynamique. Bien que beaucoup de travaux concernent le RCPSP statique, seules quelques methodes sont proposees pour le cas dynamique. De plus ces methodes ne sont pas satisfaisantes. La methode que nous proposons...

The Resource Constrained Project Scheduling Problem (rcpsp) is a general scheduling problem which... more The Resource Constrained Project Scheduling Problem (rcpsp) is a general scheduling problem which consists in scheduling a set of activities taking into account temporal and resource constraints (Demeulemeester and Herroelen, 2002). Preemption is not allowed. The objective considered here is the minimization of the makespan (total duration) of the project. This problem is NP-hard (Blazewicz et al., 1983). Most work about rcpsp consider static problems in which activities are known in advance and constraints are fixed. However, every schedule is subject to unexpected events (consider for example a new activity to schedule, or a resource failure – eg. machine breakdown). When such a situation arises, a new solution taking these events into account is needed generally in a short time. Furthermore, this new solution must preferably be not too far from the previous one. Several works concern dynamic scheduling problems. But generally, they deal with very specific problems like one-machin...

The Resource Constrained Project Scheduling Problem (rcpsp) is a general scheduling problem. It c... more The Resource Constrained Project Scheduling Problem (rcpsp) is a general scheduling problem. It consists of a set of activities and a set of renewable resources. Each resource is available in a given constant amount. Each activity has a duration and requires a constant amount of resource to be processed. Preemption is not allowed. Activities are related by two sets of constraints: temporal constraints modelled through precedence constraints, and resource constraints that state that for each time period and for each resource, the total demand cannot exceed the resource capacity. The objective considered here is the minimization of the makespan (total duration) of the project. This problem is NP-hard [3]. Most work about rcpsp consider static problems in which activities are known in advance and constraints are fixed. However, every schedule is subject to unexpected events (consider for example a new activity to schedule, or a resource failure – eg. machine breakdown). When such a sit...

Scheduling problems considered in the literature are often static (activities are known in advanc... more Scheduling problems considered in the literature are often static (activities are known in advance and constraints are fixed). However, every real-life schedule is subject to unexpected events. In these cases, a new solution is needed in a preferably short time and as close as possible to the current solution. In this paper, we present an exact approach for solving dynamic Resource-Constrained Project Scheduling Problems or RCPSP. This approach combines explanation-based constraint programming and operational research techniques. We present our first experimental results that show impressive improvements in both computation time and stability when comparing our approach to a re-execution from scratch.

This paper introduces a new method based on constraint programming (CP) and genetic algorithm (GA... more This paper introduces a new method based on constraint programming (CP) and genetic algorithm (GA) for solving dynamic scheduling problems. The proposed approach allows us to handle scheduling problems with large sizes (i.e. search spaces are too large). Our idea is to break up the search space into disjoined sub-spaces by the genetic algorithm. To each individual of the population is associated a sub-space. Each sub-space is represented by a sub-CSP which is easier to solve than the original scheduling problem. Our first experimentations are addressed to the Endoscopy Unit scheduling in dynamic way.

Publikationsansicht. 44868480. Utilisation de la programmation par contraintes pour le problème ... more Publikationsansicht. 44868480. Utilisation de la programmation par contraintes pour le problème d'allocation de fréquences en téléphonie cellulaire / (2002). Ducharme, Alain. Abstract. "Mémoire présenté en vue de l'obtention ...