Showing papers by "Mario Vanhoucke published in 2004"

On the morphological structure of a network

Abstract: In literature, both topological and resource-related measures are used to predict the difficulty of a project scheduling problem. Rapid progress regarding solution procedures has resulted in the development of a number of data generators in order to generate instances under a controlled design and in different standard sets with problem instances. These complexity measures need to serve as predictors for the complexity of the problem under study. In this paper, we report on results for the topological structure of a network. The contribution of this paper is threefold. First, we review six topological network indicators in order to describe the structure of a network in a detailed way. These indicators were originally developed by [20] and have been modified or sometimes completely replaced by alternative indicators in order to give a better description of the topology of a network. Secondly, we generate a large amount of different networks with four network generators. This allows us to draw conclusions on both the performance of different network generators and to give a critical remark on well-known datasets from literature. Our general conclusions are that none of the network generators are able to capture the complete feasible domain of all networks. Moreover, each network generator covers its own network-specific domain and, consequently, contributes to the generation of instance data sets. Finally, we perform computational results on the well-known resource-constrained project scheduling problem to proof that our indicators are reliable and have significant predictive power to serve as complexity indicators. Note

Work Continuity In A Real-Life Schedule: The Westerschelde Tunnel

Abstract: The scheduling of projects has gained increasing attention since the introduction of PERT and CPM Both the scheduling literature and the software scheduling packages rely on heuristic and optimal procedures to schedule projects under various assumptions However, there is still room for improvement by incorporating specific characteristics into the scheduling procedures In this paper we describe the scheduling of a real-life project that aims at the construction of a tunnel at the Westerschelde in the Netherlands In doing so, we show that so-called work continuity is the main issue during the scheduling phase No software package, however, is able to incorporate this requirement in an exact way We compare different possible schedules under various assumptions and prove the necessity of this new feature

An electromagnetism meta-heuristic for the resource-constrained project scheduling problem

Abstract: Recently, a new heuristic algorithm for global optimization has been proposed by Birbil and Fang (2003), referred to as Electromagnetism (EM). This technique is based on the electromagnetism theory of physics, and simulates attraction and repulsion of sample points in order to move towards an optimal solution. In this paper, we have extended the EM methodology for combinatorial optimization problems. To that purpose, we use the EM framework for solving the well-known resource-constrained project scheduling problem (RCPSP) heuristically. We rely on problem-specific characteristics to adapt the original EM framework to the problem under study. We present computational experiments on a standard benchmark dataset, compare the results of the different modifications on the original EM framework with current state-of-the-art heuristics, and show that the procedure is capable of producing consistently good results for challenging instances of the resource-constrained project scheduling problem. We also give directions for future research in order to make the EM framework competitive with the current state-of-the-art heuristics.

A hybrid scatter search / Electromagnetism meta-heuristic for project scheduling

Abstract: In the last few decades, several effective algorithms for solving the resource-constrained project scheduling problem have been proposed. However, the challenging nature of this problem, summarised in its strongly NP-hard status, restricts the effectiveness of exact optimisation to relatively small instances. In this paper, we present a new meta-heuristic for this problem, able to provide near-optimal heuristic solutions. The procedure combines elements from scatter search, a generic population-based evolutionary search method, and a recently introduced heuristic method for the optimisation of unconstrained continuous functions based on an analogy with electromagnetism theory, hereafter referred to as the electromagnetism meta-heuristic. We present computational experiments on standard benchmark datasets, compare the results with current state-ofthe- art heuristics, and show that the procedure is capable of producing consistently good results for challenging instances of the resource-constrained project scheduling problem. We also demonstrate that the algorithm outperforms state-of-the-art existing heuristics.

Work continuity constraints in project scheduling

Abstract: Repetitive projects involve the repetition of activities along the stages of the project. Since the resources required to perform these activities move from one stage to the other, a main objective of scheduling these projects is to maintain the continuity of work of these resources so as to minimize the idle time of resources. This requirement, often referred to as work continuity constraints, involves a trade-off between total project duration and the resource idle time. The contribution of this paper is threefold. Firstly, we provide an extensive literature summary of the topic under study. Although most research papers deal with the scheduling of construction projects, we show that this can be extended to many other environments. Secondly, we propose an exact search procedure for scheduling repetitive projects with work continuity constraints. This algorithm iteratively shifts repeating activities further in time in order to decrease the resource idle time. We have embedded this recursive search procedure in a horizon-varying algorithm in order to detect the complete trade-off profile between resource idle time and project duration. The procedure has been coded in Visual C++ and has been validated on a randomly generated problem set. Finally, we illustrate the concepts on three examples. First, the use our new algorithm is illustrated on a small fictive problem example from literature. In a second example, we show that work continuity constraints involve a tradeoff between total project duration and the resource idle time. A last example describes the scheduling of a well-known real-life project that aims at the construction of a tunnel at the Westerschelde in the Netherlands.