• A Bi-Population Based Genetic Algorithm for the Resource-Constrained Project Scheduling Problem

      Debels, Dieter; Vanhoucke, Mario (2005)
      The resource-constrained project scheduling problem (RCPSP) is one of the most challenging problems in project scheduling. During the last couple of years many heuristic procedures have been developed for this problem, but still these procedures often fail in finding near-optimal solutions for more challenging problem instances. In this paper, we present a new genetic algorithm (GA) that, in contrast of a conventional GA, makes use of two separate populations. This bi-population genetic algorithm (BPGA) operates on both a population of left-justified schedules and a population of right-justified schedules in order to fully exploit the features of the iterative forward/backward local search scheduling technique. Comparative computational results reveal that this procedure can be considered as today's best performing RCPSP heuristic.
    • A classification of programmes and its managerial impact

      Vereecke, Ann; Stevens, Marleen; Pandelaere, Els; Deschoolmeester, Dirk (2003)
      The paper describes the results of an exploratory research study on the application of programme management in six companies. A classification of programmes is developed that may help in understanding the differences between programmes and the managerial impact of these differences. The research shows that the formalised and rigorous approach as described in most programme management handbooks is not widely adopted. The cases show less centralisation, less formalisation and less management of the interdependencies between the projects in the programme than one would expect on the basis of the programme management literature. This is especially the case in programmes that originate as a grouping of a set of existing projects. Yet, formalisation is mentioned as the main success factor in managing programmes. Keywords: Programme management, project management, management of change
    • A comparison of different project duration forecasting methods using earned value metrics

      Vandevoorde, Stephan; Vanhoucke, Mario (2005)
      Earned value project management is a well-known management system that integrates cost, schedule and technical performance. It allows the calculation of cost and schedule variances and performance indices and forecasts of project cost and schedule duration. The earned value method provides early indications of project performance to highlight the need for eventual corrective action. Earned value management was originally developed for cost management and has not widely been used for forecasting project duration. However, recent research trends show an increase of interest to use performance indicators for predicting total project duration. In this paper, we give an overview of the state-of-the-art knowledge for this new research trend to bring clarity in the often confusing terminology. The purpose of this paper is three-fold. First, we compare the classic earned value performance indicators SV & SPI with the newly developed earned schedule performance indicators SV(t) & SPI(t). Next, we present a generic schedule forecasting formula applicable in different project situations and compare the three methods from literature to forecast total project duration. Finally, we illustrate the use of each method on a simple one activity example project and on real-life project data. Keywords: Earned value, earned duration, earned schedule, project duration forecasting
    • A finite capacity production scheduling procedure for a belgian steel company

      Debels, Dieter; Vanhoucke, Mario (2006)
      We present a finite capacity production scheduling algorithm for an integrated steel company located in Belgium. This multiple-objective optimization model takes various case-specific constraints into account and consists of two steps. A machine assignment step determines the routing of an individual order through the network while a scheduling step makes a detailed timetable for each operation for all orders. The procedure has been tested on randomly generated data instances that reflect the characteristics of the steel company. We report promising computational results and illustrate the flexibility of the optimization model with respect to the various input parameters. Keywords. Master production scheduling, manufacturing planning and control, scheduling/sequencing.
    • A Hybrid Scatter Search / Electromagnetism Meta-Heuristic for Project Scheduling

      Debels, Dieter; De Reyck, B.; Leus, Roel; Vanhoucke, Mario (2004)
    • A hybrid scatter search/electromagnetism meta heuristic for project scheduling

      Debels, Dieter; De Reyck, B.; Leus, Roel; Vanhoucke, Mario (2003)
      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-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 demonstrate that the algorithm outperforms state-of-the-art existing heuristics. Keywords: project scheduling, heuristics, scatter search, electromagnetism
    • A multi-level approach to program objectives: definitions and managerial implications

      De Hertogh, Steven; Van den broecke, Erik; Vereecke, Ann; Viaene, Stijn; Harpham, A. (2006)
      Projects are recognized as the building blocks of strategy. Outputs, outcomes, benefits and related concepts have been put forward by the program management community to bridge the gap between strategy and projects. Yet, firstly there appears to be some discordance among authors on the exact nature of these concepts. Secondly, these frameworks may not yet fully reflect the specific nature of strategy implementation. Therefore it is hard to accept them as the basis for communication between the project/program organisation and the business management when managing strategy implementation through programs of projects. We will borrow three concepts (resources, competencies and capabilities) from the resource based view of the company (RBV). We shall use them to define three levels of program objectives. We will illustrate these levels through a case of a strategic program in a professional information services company. We conclude with implications on current program management practice and research. Keywords: program management, program objectives, strategy implementation, benefits management
    • A network typology of plants in global manufacturing networks

      Vereecke, Ann; Van Dierdonck, Roland; De Meyer, Arnoud (2001)
    • A scatter search procedure for maximizing the net present value of a project under renewable resource constraints

      Vanhoucke, Mario (2006)
      In this paper, we present a meta-heuristic algorithm for the well-known resource-constrained project scheduling problem with discounted cash flows. This optimization procedure maximizes the net present value of project subject to the precedence and renewable resource constraints. The problem is known to be NP-hard. We investigate the use of a enhanced bi-directional generation scheme and a recursive forward/backward improvement method and embed them in a meta-heuristic scatter search framework. We generate a large dataset of project instances under a controlled design and report detailed computational results. The solutions and project instances can be downloaded from a website in order to facilitate comparison with future research attempts. Keywords: Resource-constrained project scheduling, Net present value, Scatter search
    • A simulation analysis of interactions between errors in costing system design

      Labro, Eva; Vanhoucke, Mario (2005)
      The academic accounting literature has established that the conditions under which costing systems in general and Activity Based Costing (ABC) in particular provide accurate costs are very stringent. Less is known, however, about the nature, level and bias of costing errors and their interactions, when these conditions are not met. The main problem to overcome to enable us to learn about these is the notion of the unobservable true cost benchmark to which to compare the costing system approximation. This paper presents a simulation method to deal with this problem, allowing a variety of research questions in this research area to be addressed with more generalizable answers. Using our methodology, we test a variety of hypotheses on the interaction between various errors in costing system design that were developed in the previous analytical, empirical, and practitioner literature. We also provide some interesting new insights on interactions between errors that were previously not discussed in the literature. This paper presents new results on (1) conditions under which partial refinement in costing systems does or does not work to improve overall accuracy, (2) the contexts in which it is most effective to correct a particular type of error in terms of improving overall accuracy and (3) indicators of robustness or sensitivity of costing system designs to errors. In doing so, we also provide insights relevant to practitioners, costing system designers and users of costing information alike. Keywords: costing system design, costing accuracy, simulation, costing errors
    • A simulation and evaluation of earned value metrics to forecast the project duration

      Vanhoucke, Mario; Vandevoorde, Stephan (2005)
      It is well-known that well managed and controlled projects are more likely to be delivered on time and within budget. The construction of a (resource-feasible) baseline schedule and the follow-up during execution are primary contributors to the success or failure of a project. Earned value management systems have been set up to deal with the complex task of controlling and adjusting the baseline project schedule during execution. Although earned value systems have been proven to provide reliable estimates for the follow-up of cost performance, it often fails to predict the total duration of the project. In this paper, we extensively review the existing methods to forecast the total project duration. Moreover, we investigate the potential of a newly developed method, the earned schedule method, which makes the connection between earned value metrics and the project schedule. We present an extensive simulation study where we carefully control the level of uncertainty in the project, the influence of the project network structure on the accuracy of the forecasts, and the time horizon where the newly developed measures provide accurate and reliable results. Keywords: Earned value, earned duration, earned schedule, CPM
    • A Typology of Plants in Global Manufacturing Networks

      Vereecke, Ann; Van Dierdonck, Roland; De Meyer, Caroline (2002)
    • An efficient hybrid search algorithm for various optimization problems

      Vanhoucke, Mario (2006)
      This paper describes a detailed study of a recursive search algorithm for different optimization problems. Although the algorithm has been originally developed for a project scheduling problem with financial objectives, we show that it can be extended to many other application areas and therefore, can serve as a sub-procedure for various optimization problems. The contribution of the paper is threefold. First, we present a hybrid recursive search procedure for the project scheduling problem with net present value maximization and compare it with state-of-the-art procedures by means of computational tests. Second, we show how the procedure can be adapted to two other application areas: project scheduling with work continuity minimization and the open pit mining problem. Last, we highlight some future research areas where this hybrid procedure might bring a promising contribution.
    • An electromagnetism meta-heuristic for the nurse scheduling problem

      Maenhout, Broos; Vanhoucke, Mario (2005)
      In this paper, we present a novel meta-heuristic technique for the nurse scheduling problem (NSP). This well-known scheduling problem assigns nurses to shifts per day taking both hard and soft constraints into account. The objective is to maximize the preferences of the nurses and to minimize the total penalty cost from violations of the soft constraints. The problem is known to be NP-hard. Due to its complexity and relevance, many algorithms have been developed to solve practical, and often case-specific versions of the NSP. The enormous amount of different constraints has led to an overwhelming amount of exact and meta-heuristic procedures, and hence comparison and state-of-the-art reporting of standard results seem to be a utopian idea. The contribution of this paper is twofold. First, we present a meta-heuristic procedure for the NSP based on the framework proposed by Birbil and Fang (2003). The Electromagnetic (EM) approach is based on the theory of physics, and simulates attraction and repulsion of sample points in order to move towards a promising solution. Second, we present computational experiments on a standard benchmark dataset, and solve problem instances under different assumptions. We show that our procedure performs consistently well under many different circumstances, and hence, can be considered as robust against case-specific constraints. Keywords: meta-heuristics, electromagnetism, nurse scheduling
    • An electromagnetism Meta-heuristic for the resource-constrained project scheduling problem

      Debels, Dieter; Vanhoucke, Mario (2005)
      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. Keywords: electromagnetism, meta-heuristics, resource-constrained project scheduling
    • Characterisation and generation of nurse scheduling problem instances

      Vanhoucke, Mario; Maenhout, Broos (2005)
      In this paper, we propose different complexity indicators for the well-known nurse scheduling problem (NSP). The NSP assigns nurses to shifts per day taking both hard and soft constraints into account. The objective is to maximize the nurses' preferences and to minimize the total penalty cost from violations of the soft constraints. The problem is known to be NP-hard. Due to its complexity and relevance in practice, the operations research literature has been overwhelmed by different procedures to solve the problem. The complexity has resulted in the development of several (meta-)heuristic procedures, able to solve a NSP instance heuristically in an acceptable time limit. The practical relevance has resulted in a never-ending amount of different NSP versions, taking practical, case-specific constraints into account. The contribution of this paper is threefold. First, we describe our complexity indicators to characterize a nurse scheduling problem instance. Secondly, we develop a NSP generator to generate benchmark instances to facilitate the evaluation of existing and future research techniques. Finally, we perform some preliminary tests on a simple IP model to illustrate that the proposed indicators can be used as predictors of problem complexity. Keywords: Nurse scheduling, Benchmark instances, Problem classification