Cherif Sadfi

An improved approximation algorithm for the single machine total completion time scheduling problem with availability constraints

In this paper, we study the single machine total completion scheduling problem subject to a period of maintenance. We propose an approximation algorithm to solve the problem with a worst case error bound of 3/17. Furthermore, an example is provided to show that the bound is tight. Computational experiments and an analysis are given afterwards.

An improved heuristic and an exact algorithm for the 2D strip and bin packing problem

In this paper, we consider a two-dimensional (2D) packing problem. It consists of packing a given set of rectangular items either into a strip with a fixed width and infinite height or into identical bins. This problem has industrial applications such as cutting glass and Very-Large-Scale Integration (VLSI) design. The guillotine constraint is imposed in this paper. For this problem, we propose some strategies to improve the Shelf Heuristic Filling (SHF) introduced by Ben Messaoud et al. (2003). In a second part, we present a branch-and-bound algorithm for the 2D Strip Packing (2SP) problem that uses a new lower bound and the improved heuristic. All our algorithms are tested on generated and literature-based instances and give good results compared to the existing algorithms.

Branch and bound and dynamic programming to minimize the total completion times on a single machine with availability constraints

In this paper we consider the single machine scheduling problem with availability constraints in order to minimize the total completion times of jobs. We propose two exact approaches to solve the problem: a dynamic programming and a branch and bound method. The study of these approaches is carried out in this article and a concluding analysis based on several experimental results allows us to select the most suitable method according to the studied instance.

A Branch and Bound Algorithm for solving the 2D Strip Packing Problem

In this paper we consider the two dimensional strip packing problem with guillotine cuts. The problem consists on packing a set of rectangular items on one strip of width W and infinite height. The items packed without overlapping, must be extracted by a series of cuts that go from one edge to the opposite edge (guillotine constraint). For this problem, we give a new lower bound based on decomposing the set of the items in sub-sets. This lower bound is used in a branch and bound algorithm to solve the problem to optimality. Computational results are presented to show the performance of both the lower bound and the exact algorithm

A branch-and-bound method for the single-machine scheduling problem under a non-availability constraint for maximum delivery time minimization

We consider the single machine scheduling problem with release dates and tails, provided that the machine is unavailable during a fixed interval. We aim to minimize the maximum delivery time under the nonresumable senario. This problem is strongly NP-hard. The proposed algorithm is based on a branch-and-bound method. We use Jacksons preemptive algorithm with precedence constraints to compute the lower bound and Schrages sequence as an upper bound. Numerical experiments show that the algorithm can solve large-size instances with up to 1000 jobs.

An iterative lower bound algorithm for the single-machine scheduling problem under a non-availability constraint for maximum delivery time minimization

We consider the single machine scheduling problem with release dates and tails, provided that the machine is unavailable during a fixed interval. This problem is strongly NP-hard. We use the Jacksons preemptive algorithm with precedence constraints to compute a lower bound and the Schrages sequence as an upper bound. Then, we propose an improved lower bound which is based on an iterative procedure. Numerical experiments show the effectiveness of the bounds.

A Column Generation Method for the Parallel-Machine Scheduling Problem with availability constraint

In this paper, we study the problem of scheduling jobs on identical parallel machines with the objective of minimizing the total completion times of jobs where each machine is subject to one unavailability time interval. We provide a column generation based method to obtain a lower bound for the problem. Computational experiments show the interest and the versatility of the proposed method

Optimization of integrated employee timetabling and Hybrid Job Shop Scheduling under time lag constraints

This paper studies two important problems, often encountered in the manufacturing industry and particularly in the tanneries: human resources planning and production scheduling. In this work, we focus on the problem that integrates Employee Timetabling [ETP] by considering their skills under various constraints, with a Hybrid Job-Shop Scheduling [HJS] under time lag constraints. After presenting and formulating our problem as a Mixed Linear Program, we propose a resolution method based on decomposition and cut generation by combining Mixed Linear Programming and Constraint Programming. Using numerical experimentations, we show the advantage of decomposition and cut generation, in terms of resolution time.

Lower bounds for total weighted completion scheduling problem with availability constraints

In this paper we consider the single machine total weighted completion scheduling problem with availability constraints. The machine is subject to many periods of maintenances. To solve this problem, we propose some lower bounds. A computational experiments and analysis are given afterwards to test the efficiency of the proposed lower bounds.

Total weighted completion scheduling problem with availability constraints

In this paper we consider the single machine scheduling problem with availability constraints in order to minimize the total weighted completion times of jobs. To solve this problem, we propose three heuristics. A computational experiments and analysis are given afterwards to test the efficiency of the proposed heuristics.