Arno Sprecher

PSPLIB - A project scheduling problem library : OR Software - ORSEP Operations Research Software Exchange Program

Abstract We present a set of benchmark instances for the evaluation of solution procedures for single- and multi-mode resource-constrained project scheduling problems. The instances have been systematically generated by the standard project generator ProGen. They are characterized by the input-parameters of ProGen. The entire benchmark set including its detailed characterization and the best solutions known so-far are available on a public ftp-site. Hence, researchers can download the benchmark sets they need for the evaluation of their algorithms. Additionally, they can make available new results. Depending on the progress made in the field, the instance library will be continuously enlarged and new results will be made accessible. This should be a valuable and driving source for further improvements in the area of project type scheduling.

Multi-mode resource-constrained project scheduling by a simple, general and powerful sequencing algorithm

In this paper we present an exact solution procedure of the branch-and-bound type for solving the multi-mode resource-constrained project scheduling problem. The basic enumeration scheme is enhanced by search tree reduction schemes which highly increase the performance of the algorithm. Among the benefits of the approach are ease of description, ease of implementation, ease of generalization, and, additionally, superior performance of the exact approach as well as reasonable heuristic capabilities of the truncated version. The procedure has been coded in C and implemented on a personal computer. Using the standard project generator ProGen we have established a wide range of instances. More than 10,000 problem instances have been systematically generated to evaluate the algorithms performance. The experimental investigation illustrates: First, the effect of the bounding rules. Second, the superior performance of the exact approach and the capabilities of the truncated version; the size of the projects that can be solved to optimality has been nearly doubled. Third, the impact of the variation of several project characteristics on solution time and quality.

Semi-active, active and non-delay schedules for the resource-constrained project scheduling problem

We consider the resource-constrained project scheduling problem (RCPSP). The focus of the paper is on a formal definition of semi-active, active, and non-delay schedules. Traditionally these schedules establish basic concepts within the job shop scheduling literature. There they are usually defined in a rather informal way which does not create any substantial problems. Using these concepts in the more general RCPSP without giving a formal definition may cause serious problems. After providing a formal definition of semi-active, active, and non-delay schedules for the RCPSP we outline some of these problems occurring within the disjunctive arc concept.

An exact algorithm for project scheduling with multiple modes

We consider an extension of the classical resource-constrained project scheduling problem (RCPSP), which covers discrete resource-resource and time-resource tradeoffs. As a result a project scheduler is permitted to identify several alternatives or modes of accomplishment for each activity of the project. The solution procedure to be presented is a considerable generalization of the branch-and-bound algorithm proposed by Demeulemeester and Herroelen, which is currently the most powerful method for optimally solving the RCPSP. More precisely, we extend their concept of delay alternatives by introducing mode alternatives. The basic enumeration scheme is enhanced by dominance rules which increase the performance of the algorithm. We then report on our computational results obtained from the comparison with the most rapid procedure reported in the literature.ZusammenfassungWir betrachten eine Erweiterung des klassischen Resource-Constrained Project Scheduling Problems (RCPSP), die die Abbildung von Ressourcen-Ressourcen- und Zeit-Ressourcen-Tradeoffs ermöglicht. Damit ist der Projektplaner in der Lage, für jeden Vorgang des Projekts mehrere Ausführungsalternativen (Modi) anzugeben. Der von uns vorgestellte Algorithmus ist eine Verallgemeinerung des derzeit schnellsten Branch-and-Bound-Verfahrens für das RCPSP von Demeulemeester und Herroelen. Wir erweitern deren Konzept der Delay-Alternativen um sogenannte Modus-Alternativen. Die Enumeration wird mit Hilfe von Dominanzregeln beschleunigt. Schließlich fassen wir unsere Rechenergebnise zusammen, in denen wir unser Verfahren mit dem derzeit schnellsten aus der Literatur bekannten Algorithmus vergleichen.

Benchmark instances for project scheduling problems

With the development of project scheduling models and methods arose the need for data instances in order to benchmark the solution procedures. Generally, benchmark instances can be distinguished by their origin into real world problems and artificial problems. The analysis of algorithmic performance on real world problem instances is of a high practical relevance, but at the same time it is only an analysis of individual cases. Consequently, general conclusions about the algorithms cannot be drawn. A solution procedure which shows very good performance on one real world instance might produce poor results on another. In order to allow a systematic evaluation of the performance of algorithms, characteristics of the projects have to be identified. The characteristics can then serve as the parameters for the systematic generation of artificial instances. The variation of the levels of these problem parameters in a full factorial design study allows to produce a set of well-balanced instances (cf. Montgomery 1976).

An Artificial Intelligence Approach

In this chapter we will use a logic programming approach in order to attack the scheduling problems described. Preliminary studies can be found in [46].

A note on “hierarchical models for multi-project planning and scheduling”

Abstract We consider the multi-mode resource-constrained project scheduling problem. The focus of our analysis is on an algorithm recently proposed by Speranza and Vercellis for finding makespan minimal solutions. The correctness of the algorithm is examined. By counterexamples we illustrate that the algorithm does not generally find (existing) optimal solutions.

Network decomposition techniques for resource-constrained project scheduling

The purpose of this paper is to study an obvious but unexplored approach for scheduling resource-constrained projects. The approach combines elements of heuristic and exact solution procedures. The project considered is decomposed into subprojects, the subproblems are optimally solved, and the solutions are concatenated. The strategy is tested on the benchmark instances of ProGeu. Several of the best known makespans collected in PSPLIB are improved. The algorithm has reduced more best known makespans than the state-of-the-art heuristic for medium-sized projects. The decomposition approach outperforms the truncated version of the branch-and-bound algorithm employed. On average, the quality of the overall solution depends on the size of the subproblems, and on the quality of the solutions of the subproblems—if approximately solved. Consequently, on the one hand, the approach benefits from the progress made in the development of exact solution procedures. But, on the other hand, the results question the rigid construction of schedules by conventional algorithms relying on extensions of partial schedules, and thus provide fundamental insights into the development of exact solution procedures.

Dynamic search tree decomposition for balancing assembly lines by parallel search

We consider the simple assembly line balancing problem of type 1 (SALB-1). Although several branch-and-bound algorithms have been developed for optimally solving the SALB-1, until now to the best of our knowledge no parallel approach has been presented for this classical problem. In this paper we propose a parallel algorithm for solving the SALB-1. The parallel approach is based on a competitive serial algorithm. The parallel approach benefits from the substitution of a powerful but memory-intensive dominance concept through solution characteristics. Using the master-slave principle the master dynamically generates subproblems which are, upon request, assigned to the slaves for evaluation. The subproblems depend on previously assigned and on previously evaluated subproblems. The characteristics allow each slave to decide on potential dominances without requiring information from another slave or the master. The algorithm has been coded in GNU C using the Parallel Virtual Machine to allow process communication. Experimental studies have been performed on a simulated cluster of personal computers. Benchmark sets from the literature served as a testbed. The computational results are extremely promising. It seems that the SALB-1 is an ideal application of parallel search.

Resource- and Time Window-Constraint Production Scheduling With Alternative Process Plans: An Artificial Intelligence Approach

Make-to-order production of customer-made products has to be done with respect to product-specific time windows by efficient utilization of manufacturing resources. Most of the traditional production scheduling approaches are based on the assumption that for each part only one process plan is available. A manufacturing system with alternative process plans is supposed to increase throughput rate via eliminating bottlenecks and handling machine breakdowns [1].