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Dive into the research topics where Issmail El Hallaoui is active.

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Featured researches published by Issmail El Hallaoui.


Operations Research | 2014

Integral Simplex Using Decomposition for the Set Partitioning Problem

Abdelouahab Zaghrouti; François Soumis; Issmail El Hallaoui

Since the 1970s, several authors have studied the structure of the set partitioning polytope and proposed adaptations of the simplex algorithm that find an optimal solution via a sequence of basic integer solutions. Balas and Padberg in 1972 proved the existence of such a sequence with nonincreasing costs, but degeneracy makes it difficult to find the terms of the sequence. This paper uses ideas from the improved primal simplex to deal efficiently with degeneracy and find subsequent terms in the sequence. When there is no entering variable that leads to a better integer solution, the algorithm referred to as the integral simplex using decomposition algorithm uses a subproblem to find a group of variables to enter into the basis in order to obtain such a solution. We improve the Balas and Padberg results by introducing a constructive method that finds this sequence by only using normal pivots on positive coefficients. We present results for large-scale problems with up to 500,000 variables for which optimal integer solutions are often obtained without any branching.


Annals of Operations Research | 2014

Flow-based integer linear programs to solve the weekly log-truck scheduling problem

Nizar El Hachemi; Issmail El Hallaoui; Michel Gendreau; Louis-Martin Rousseau

In this paper we present the solution to a weekly log-truck scheduling problem (LTSP) integrating the routing and scheduling of trucks where all goods are transported in full truckloads. We must take into account pick-up and delivery requirements, multiple products, inventory levels, and lunch breaks. The objective is to minimize the overall transportation cost including wait times and the empty and loaded distance traveled. Our solution is based on a two-phase approach. The first phase involves an integer linear program that determines the destinations of full truckloads. The second phase uses an implicit integer linear program based on an arc formulation to ensure that the trucks are routed and scheduled at a minimum cost. Experiments have been conducted using Cplex 12.4.0, and almost all instances were solved within six hours with a reasonable gap.


Journal of Intelligent Manufacturing | 2018

A two-phase approach to solve the synchronized bin–forklift scheduling problem

Nizar El Hachemi; Mohammed Saddoune; Issmail El Hallaoui; Louis-Martin Rousseau

In this paper, we propose a two-phase approach to solve a combined routing and scheduling problem that occurs in the textile industry: fabrics are dyed by dye-jets and transported by forklifts. The objective is to minimize the cost of the unproductive activities, i.e., the dye-jet setup times and the forklift waiting time. The first phase solves an integer linear program to assign jobs (fabrics) to dye-jets while minimizing the setup cost; we compare an arc-based and a path-based formulation. The second phase uses a mixed-integer linear program for the dye-jet scheduling and both the routing and scheduling of forklifts. Experiments are performed on real data provided by a major multinational company, and larger test problems are randomly generated to assess the algorithm. The tests were conducted using Cplex 12.6.0 and a column generation solver. The numerical results show that our approach is efficient in terms of both solution quality and computational time.


SpringerPlus | 2016

Multilevel hybrid method for optimal buffer sizing and inspection stations positioning

Fatima Zahra Mhada; Mohamed Ouzineb; Robert Pellerin; Issmail El Hallaoui

Designing competitive manufacturing systems with high levels of productivity and quality at a reasonable cost is a complex task. Decision makers must face numerous decision variables which involve multiple and iterative analysis of the estimated cost, quality and productivity of each design alternative. This paper adresses this issue by providing a fast algorithm for solving the buffer sizing and inspection positioning problem of large production lines by combining heuristic and exact algorithms. We develop a multilevel hybrid search method combining a genetic algorithm and tabu search to identify promising locations for the inspection stations and an exact method that optimizes rapidly (in polynomial time) the buffers’ sizes for each location. Our method gives valuable insights into the problem, and its solution time is a small fraction of that required by the exact method on production lines with 10–30 machines.


EURO Journal on Computational Optimization | 2018

Improved integral simplex using decomposition for the set partitioning problem

Abdelouahab Zaghrouti; Issmail El Hallaoui; François Soumis

Integral simplex using decomposition (ISUD) is a method that efficiently solves set partitioning problems. It is an iterative method that starts from a known integer solution and moves through a sequence of integer solutions, decreasing the cost at each iteration. At each iteration, the method decomposes the original problem into a reduced problem (RP) and a complementary problem (CP). Given an integer solution to RP (that is also solution to the original problem), CP finds a descent direction having the minimum ratio between its cost and the number of its positive variables. We loop on until an optimal or near-optimal solution to the original problem is reached. In this paper, we introduce a modified model for CP. The new model finds a descent direction that minimizes the ratio between the cost of the direction and an overestimation of the number of variables taking one in the next solution. The new CP presents higher chances of finding improved integer solutions without branching. We present results for the same large instances (with up to 570,000 columns) as the ones previously used to test ISUD. For all the instances, optimality is always reached with a speedup factor of at least five.


international conference on advances in production management systems | 2014

A Hybrid Method for Solving Buffer Sizing and Inspection Stations Allocation

Mohamed Ouzineb; Fatima Zahra Mhada; Robert Pellerin; Issmail El Hallaoui

The buffer sizing problem in unreliable production lines is an important, indeed, complex combinatorial optimization problem with many industrial applications. These applications include quality, logistics and manufacturing production systems. In the formulation of the problem, the system consists of n machines, n fixed-size buffers and m inspection station in series. The objective is to minimize a combined storage and shortage costs, and also specifying the optimal location of inspection stations in the system. The present paper aims at optimizing a generalization of the model previously proposed in (Mhada et al., 2014) using a novel approach. In this approach, we combine Tabu Search (TS) and Genetic Algorithm (GA) to identify search regions with promising locations of inspection stations and an exact method to optimize the assignment of buffer sizes for each location. This approach provides a balance between diversification and intensification. Numerical results on test problems from previous research are reported. Using this approach, we can reduce the solution time by more than 97% in some cases.


Infor | 2013

Buffer dimensioning and control stations positioning with a space partitioning-tabu search approach

Mohamed Ouzineb; Fatima Zahra Mhada; Issmail El Hallaoui

Abstract We propose an efficient heuristic method based on Space Partitioning (SP) and Tabu Search (TS) to solve the buffer sizing problem in unreliable production lines with several inspection stations. In such problem, we have an unreliable production line consisting of a certain number of machines and fixed-size buffers. These machines produce a single part with two different quality levels: conforming and non-conforming parts. The production line may contain inspection stations whose job is to reject the non-conforming parts from the line. The production line must meet a constant rate of demand for the conforming finished parts. The objective is to minimize the average long term combined storage and shortage costs, while also specifying the optimal location of inspection stations. This design problem is a difficult mixed integer nonlinear program. Solving even a small instance of 10 machines and one inspection station using a direct dynamic programming method takes hours. If we especially increase the number of machines or the inspection stations, the dynamic programming approach becomes drastically inefficient. The method we propose divides the search space into a set of disjoint subspaces using a space partitioning technique. Tabu search is used to intensify the search in the selected subspaces. This combined method finds optimal solutions for small instances in a fraction of dynamic programming time. For the largest instances (up to 20 machines) the dynamic programming approach was unable to solve, our method finds high-quality solutions in reasonable times.


Les Cahiers du GERAD | 2013

Integral simplex using decomposition with primal cuts

Issmail El Hallaoui; François Soumis; Samuel Rosat; Andrea Lodi


Les Cahiers du GERAD | 2003

Dynamic Aggregation of Set Partitioning Constraints in Column Generation

Guy Desaulniers; Issmail El Hallaoui; François Soumis; Daniel Villeneuve


Les Cahiers du GERAD | 2014

Influence of the normalization constraint on the integral simplex using decomposition

Issmail El Hallaoui; François Soumis; Samuel Rosat; Driss Chakour

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François Soumis

École Polytechnique de Montréal

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Guy Desaulniers

École Polytechnique de Montréal

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Fatima Zahra Mhada

École Polytechnique de Montréal

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Robert Pellerin

École Polytechnique de Montréal

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Mohammed Saddoune

École Polytechnique de Montréal

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Abdelouahab Zaghrouti

École Polytechnique de Montréal

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Samuel Rosat

École Polytechnique de Montréal

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Louis-Martin Rousseau

École Polytechnique de Montréal

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François Soumis

École Polytechnique de Montréal

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Abdelmoutalib Metrane

École Polytechnique de Montréal

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