Improving metaheuristic performance by evolving a variable fitness function.

In this paper we study a complex real world workforce scheduling problem. We apply constructive search and variable neighbourhood search (VNS) metaheuristics and enhance these methods by using a variable fitness function. The variable fitness function (VFF) uses an evolutionary approach to evolve weights for each of the (multiple) objectives. The variable fitness function can potentially enhance any search based optimisation heuristic where multiple objectives can be defined through evolutionary changes in the search direction. We show that the VFF significantly improves performance of constructive and VNS approaches on training problems, and ¿learn¿ problem features which enhance the performance on unseen test problem instances

Resource constrained routing and scheduling: Review and research prospects

In the service industry, it is crucial to efficiently allocate scarce resources to perform tasks and meet particular service requirements. What considerably complicates matters is when these resources, for example skilled technicians, nurses, and home carers have to visit different customer locations. This paper provides a comprehensive survey on resource constrained routing and scheduling that unveils the problem characteristics with respect to resource qualifications, service requirements and problem objectives. It also identifies the most effective exact and heuristic algorithms for this class of problems. The paper closes with several research prospects

Enhancing the Performance of Search Heuristics. Variable Fitness Functions and other Methods to Enhance Heuristics for Dynamic Workforce Scheduling.

Scheduling large real world problems is a complex process and finding high quality solutions is not a trivial task. In cooperation with Trimble MRM Ltd., who provide scheduling solutions for many large companies, a problem is identified and modelled. It is a general model which encapsulates several important scheduling, routing and resource allocation problems in literature. Many of the state-of-the-art heuristics for solve scheduling problems and indeed other problems require specialised heuristics tailored for the problem they are to solve. While these provide good solutions a lot of expert time is needed to study the problem, and implement solutions. This research investigates methods to enhance existing search based methods. We study hyperheuristic techniques as a general search based heuristic. Hyperheuristics raise the generality of the solution method by using a set of tools (low level heuristics) to work on the solution. These tools are problem specific and usually make small changes to the problem. It is the task of the hyperheuristic to determine which tool to use and when. Low level heuristics using exact/heuristic hybrid method are used in this thesis along with a new Tabu based hyperheuristic which decreases the amount of CPU time required to produce good quality solutions. We also develop and investigate the Variable Fitness Function approach, which provides a new way of enhancing most search-based heuristics in terms of solution quality. If a fitness function is pushing hard in a certain direction, a heuristic may ultimately fail because it cannot escape local minima. The Variable Fitness Function allows the fitness function to change over the search and use objective measures not used in the fitness calculation. The Variable Fitness Function and its ability to generalise are extensively tested in this thesis. The two aims of the thesis are achieved and the methods are analysed in depth. General conclusions and areas of future work are also identified

Procurement and strategy in manufacturing firms

The strategic role of the Procurement function in manufacturing firms has received increased attention in the literature over the past two decades. Before the 1970s, the supply environment was seen to be stable for most firms, with no particular strategic opportunities or threats. Procurement was treated as an administrative or service function. The oil crisis in the early 1970s changed the situation, bringing in its wake acute inflation and material shortages. The 1980s saw a revolution in manufacturing with the advent of JIT, increased automation and global operations. Theoretical researchers saw the potential for a proactive and strategic role for the Procurement function. This was, however, not reflected in empirical research, which failed to find consistent evidence of firms considering Procurement as strategic. This thesis addresses the gap between precept and practice evident in the literature. A major criticism of the empirical literature is the treatment of the strategic (value) activities on the supply side and the activities of the Procurement department as synonymous. This thesis questioned that view and made a distinction between the two activities. A theoredcal framework was built up from the literature to identify the contexts in which Supply considerations would be strategic. Propositions were generated which allowed for strategic Supply activities both through the Procurement department as well as outside it. The empirical work looked at 25 UK manufacturing firms through the case study approach. The cases were scrutinised for evidence of strategic activities on the supply side, as well as the strategic importance of the Procurement department. The results confirmed that (1) Supply considerations were strategic for a majority of firms. (2) Strategic consideration of Supply depended on a number of contingent variables.(3) Strategic Supply activities were not necessarily reflected in the strategic importance given to the Procurement department

Problemas de localização-distribuição de serviços semiobnóxios: aproximações e apoio à decisão

Doutoramento em Gestão IndustrialA presente tese resulta de um trabalho de investigação cujo objectivo se centrou no problema de localização-distribuição (PLD) que pretende abordar, de forma integrada, duas actividades logísticas intimamente relacionadas: a localização de equipamentos e a distribuição de produtos. O PLD, nomeadamente a sua modelação matemática, tem sido estudado na literatura, dando origem a diversas aproximações que resultam de diferentes cenários reais. Importa portanto agrupar as diferentes variantes por forma a facilitar e potenciar a sua investigação. Após fazer uma revisão e propor uma taxonomia dos modelos de localização-distribuição, este trabalho foca-se na resolução de alguns modelos considerados como mais representativos. É feita assim a análise de dois dos PLDs mais básicos (os problema capacitados com procura nos nós e nos arcos), sendo apresentadas, para ambos, propostas de resolução. Posteriormente, é abordada a localização-distribuição de serviços semiobnóxios. Este tipo de serviços, ainda que seja necessário e indispensável para o público em geral, dada a sua natureza, exerce um efeito desagradável sobre as comunidades contíguas. Assim, aos critérios tipicamente utilizados na tomada de decisão sobre a localização destes serviços (habitualmente a minimização de custo) é necessário adicionar preocupações que reflectem a manutenção da qualidade de vida das regiões que sofrem o impacto do resultado da referida decisão. A abordagem da localização-distribuição de serviços semiobnóxios requer portanto uma análise multi-objectivo. Esta análise pode ser feita com recurso a dois métodos distintos: não interactivos e interactivos. Ambos são abordados nesta tese, com novas propostas, sendo o método interactivo proposto aplicável a outros problemas de programação inteira mista multi-objectivo. Por último, é desenvolvida uma ferramenta de apoio à decisão para os problemas abordados nesta tese, sendo apresentada a metodologia adoptada e as suas principais funcionalidades. A ferramenta desenvolvida tem grandes preocupações com a interface de utilizador, visto ser direccionada para decisores que tipicamente não têm conhecimentos sobre os modelos matemáticos subjacentes a este tipo de problemas.This thesis main objective is to address the location-routing problem (LRP) which intends to tackle, using an integrated approach, two highly related logistics activities: the location of facilities and the distribution of materials. The LRP, namely its mathematical formulation, has been studied in the literature, and several approaches have emerged, corresponding to different real-world scenarios. Therefore, it is important to identify and group the different LRP variants, in order to segment current research and foster future studies. After presenting a review and a taxonomy of location-routing models, the following research focuses on solving some of its variants. Thus, a study of two of the most basic LRPs (capacitated problems with demand either on the nodes or on the arcs) is performed, and new approaches are presented. Afterwards, the location-routing of semi-obnoxious facilities is addressed. These are facilities that, although providing useful and indispensible services, given their nature, bring about an undesirable effect to adjacent communities. Consequently, to the usual objectives when considering their location (cost minimization), new ones must be added that are able to reflect concerns regarding the quality of life of the communities impacted by the outcome of these decisions. The location-routing of semi-obnoxious facilities therefore requires to be analysed using multi-objective approaches, which can be of two types: noninteractive or interactive. Both are discussed and new methods proposed in this thesis; the proposed interactive method is suitable to other multi-objective mixed integer programming problems. Finally, a newly developed decision-support tool to address the LRP is presented (being the adopted methodology discussed, and its main functionalities shown). This tool has great concerns regarding the user interface, as it is directed at decision makers who typically don’t have specific knowledge of the underlying models of this type of problems

Reengineering BPR: a critical exploration

Purpose and aims of the thesis: This thesis critically reviews the current BPR literature through the perspective of the systemic/holistic management thinking, in such a way as to bring the study of BPR into a new era. Central to this holistic type of thinking are the concepts of Processes, Radicality, IT/IS, Culture and Human Element awareness: these concepts are used to explore core publications in reengineering literature. More specifically the aims of the thesis are to (i) explain why BPR needs redefining, (ii) redefine it as a holistic activity, (iii) provide guidelines to do that and also (iv) show the feasibility of this approach.Research Method: For the achievement of the above aims, a combination of research methodology strategies and techniquesw as used.T hesei nclude a documentary review approach and a comparative analysis for gathering and disseminating the data. These were complemented by case study material, which is used to assess the plausibility of the suggestions made in this particular thesis.Findings: While exploring the notion of BPR it was identified that (i) the notion has no universally accepted definition, (ii) largely the definitions and numerous core reengineering readings (Davenport 1993, Johansson et al.1993, etc.) give emphasis to different extreme orientations (e.g., IT oriented, processes oriented) and thereby attract negative criticism (Jones 1996, Case 1999), (iii) there is no code of practice (no formal guidelines) when practising reengineering, and largely (iv) there is a great amount of inconsistency between what the examined BPR authors say they do, and what they actually do in practice (e. g., Hammer and Champy 1993).Recommendations: Recognising the novel link between a number of major fields of activity (Processes, Radicality, IT/IS, Culture and Human Element), enabled a new holistic definition and a new form of guidelines to emerge, and be operationalised; that is, for this author to present a set of theoretical and practical ways of improving the BPR managerial tool. Such guidance, though, is not intended to be sterile and staid. Indeed, this guidance will itself incorporate critical thinking around the issues involved in an intervention like BPR, by the further enhancement of multi disciplinary discourse about organisational learning and awareness. It is concluded that this set of recommended guidelines could provide a framework for an enriched, holistic and successful BPR initiative