Browsing by Subject "Operations Research"

Now showing 1 - 9 of 9
  • Thumbnail Image
    Item
    Open Access
    The address sort and other computer sorting techniques
    (1971) Underhill, Leslie G; Troskie, Casper G
    Originally this project was to have been a feasibility study of the use of computers in the library. It soon became clear that the logical place in the library at which to start making use of the computer was the catalogue. Once the catalogue was in machine-readable form it would be possible to work backwards to the book ordering and acquisitions system and forwards to the circulation and book issue system. One of the big advantages in using the computer to produce the catalogue would be the elimination of the "skilled drudgery" of filing. Thus vast quantities of data would need to be sorted. And thus the scope of this project was narrowed down from a general feasibility study, firstly to a study of a particular section of the library and secondly to one particularly important aspect of that section - that of sorting with the aid of the computer. I have examined many, but by no means all computer sorting techniques, programmed them in FORTRAN as efficiently as I was able, and compared their performances on the IBM 1130 computer of the University of Cape Town. I have confined myself to internal sorts, i.e. sorts that take place in core. This thesis stops short of applying the best of these techniques to the library. I intend however to do so, and to work back to the original scope of my thesis.
  • Thumbnail Image
    Item
    Open Access
    The development of an operational management procedure for the South African west coast rock lobster fishery
    (1998) Johnston, Susan Joy; Butterworth, Doug S; Stewart, Theodor J
    This thesis considers the development of an operational management procedure (OMP) to provide scientific recommendations for commercial TAC for the South African west coast rock lobster (Jasus lalandii) fishery. This fishery has been under considerable stress in recent years as a result of overfishing and low somatic growth rates. Present catch levels, less than 2000 MT, are substantially smaller than levels recorded in the past. The present biomass (above 75mm carapace length) is estimated to be only six percent of the pristine level. At the start of this research, no long-term management strategy for the resource existed. Neither was there any robust, tested, scientific method available for setting the annual TAC for the fishery, which resulted in a time-consuming and unsatisfactory scientific debate each year in developing a series of ad hoc TAC recommendations. The work presented in this thesis is thus aimed at answering two important questions. i) Can an adequate mathematical model be developed as a basis to simulate the resource and its associated fishery? ii) Can a self-correcting robust OMP be developed for the resource? The first phase of this thesis is the development of a size-structured population model of the resource and the associated fishery. A size-structured model is necessary as lobsters are difficult to age and hence most of the data collected are on a size basis. Furthermore, important management issues, such as the legal minimum size which has changed over time, require a model able to take size-structure into account. This model is fitted to a wide range of data from the fishery, including CPUE (catch-per-unit-effort) and catch-at-size information, by maximising a likelihood function. The model is shown to fit reasonably well to all data, and to provide biologically plausible estimates for its six estimable parameters.
  • Thumbnail Image
    Item
    Open Access
    An examination of heuristic algorithms for the travelling salesman problem
    (1988) Höck, Barbar Katja; Stewart, Theodor J
    The role of heuristics in combinatorial optimization is discussed. Published heuristics for the Travelling Salesman Problem (TSP) were reviewed and morphological boxes were used to develop new heuristics for the TSP. New and published heuristics were programmed for symmetric TSPs where the triangle inequality holds, and were tested on micro computer. The best of the quickest heuristics was the furthest insertion heuristic, finding tours 3 to 9% above the best known solutions (2 minutes for 100 nodes). Better results were found by longer running heuristics, e.g. the cheapest angle heuristic (CCAO), 0-6% above best (80 minutes for 100 nodes). The savings heuristic found the best results overall, but took more than 2 hours to complete. Of the new heuristics, the MST path algorithm at times improved on the results of the furthest insertion heuristic while taking the same time as the CCAO. The study indicated that there is little likelihood of improving on present methods unless a fundamental new approach is discovered. Finally a case study using TSP heuristics to aid the planning of grid surveys was described.
  • Thumbnail Image
    Item
    Open Access
    Interactive methods for multiple objective linear programming in decision support
    (2005) Makaya, Makaya L; Stewart, Theodor
    Includes bibliographical references (leaves 144-155).
  • Thumbnail Image
    Item
    Open Access
    Mathematical modelling and risk management in deregulated electricity markets
    (2005) Davis, Stephen; Stewart, Theodor J
    In this thesis we aim to explore how electricity generation companies cope with the transition to a competitive environment in a newly deregulated electricity industry. Analyses and discussions are generally performed from the perspective of a Generator/Producer, otherwise they are undertaken with respect to the market as a whole. The techniques used for tackling the complex issues are diverse and wide-ranging as ascertained from the existing literature on the subject. The global ideology focuses on combining two streams of thought: the production optimisation and equilibrium techniques of the old monopolistic, cost-saving industry and; the new dynamic profit-maximising and risk-mitigating competitive industry. Financial engineering in a new and poorly understood market for electrical power must now take place in conjunction with - yet also constrained by - the physical production and distribution of the commodity.
  • Thumbnail Image
    Item
    Open Access
    A multivariate analysis of shares listed on the Johannesburg Stock Exchange
    (1983) Visser, Francesca; Affleck-Graves , J F
    This thesis examines the usefulness of multivariate statistical techniques to portfolio theory by applying two different multivariate techniques to two separate classificatory problems concerning shares listed on the Johannesburg Stock Exchange. In Chapter 1 the two techniques and two classificatory problems are introduced and their context within the general structure of portfolio theory is explained. Chapter 2 gives a theoretical overview of the first technique used, namely Factor Analysis. Chapters 3 and 4 discuss the application of factor analytic techniques to shares listed on the Johannesburg Stock Exchange. Chapter 5 gives a theoretical overview of Multiple Discriminant Analysis, the second multivariate technique used. Chapter 6 represents a survey of previous applications of Multiple Discriminant Analysis in the field of Finance, while Chapters 7 and 8 discuss the application of this technique to shares listed on the Johannesburg Stock Exchange. Finally, Chapter 9 gives a brief summary of the main conclusions in this thesis.
  • Thumbnail Image
    Item
    Open Access
    Planning for the strategic management of South Africa's West Coast rock lobster fishery : an integrated approach to group decision support
    (1998) Malyon, Brett Edwin; Stewart, Theodor J
    As Bryson (1995) points out, strategic planning is particularly useful for assisting organisations and communities to deal with change. This study was carried out at a time of great change in South Africa, when a new fisheries policy was being formulated and negotiated. The research describes an intervention with a group of .fisheries managers, scientists, fishing company directors and other key stakeholders, in planning for the future management of the West Coast Rock Lobster fishery. The primary objective of the study was to consider an integrated approach to group decision support, incorporating a particular soft-OR approach, SODA, together with multi-criteria decision analysis (MCDA). An integration of these two approaches has recently been suggested by researchers, for several reasons. Firstly, different phases of an intervention usually involve different tasks. Secondly, mixing methodologies will enable different aspects of the problem to be modelled and analysed. SODA was used at the outset, for divergent exploration and structuring of the problems surrounding the development of an operational management procedure (OMP) for the fishery, including more subjective and qualitative information. Several stakeholder groups opposed the idea of an OMP in the form in which it was proposed.
  • Thumbnail Image
    Item
    Open Access
    Robustness analysis based on weight restrictions in data envelopment analysis
    (2006) Kantu, Dieudonne Kabongo; Stewart, Theodor J
    Evaluating the performance of organisations is essential to good planning and control. Part of this process is monitoring the performance of organisations against their goals. The comparative efficiency of organizations using common inputs and outputs makes it possible for organizations to improve their performance so that can operate as the most efficient organizations. Resources and outputs can be very diversified in nature and it is complex to assess organizations using such resources and outputs. Data Envelopment Analysis models are designed to facilitate this of assessment and aim to evaluate the relative efficiency of organisations. Chapter 2 is dedicated to the basic Data Envelopment Analysis. We present the following: * A review of the Data Envelopment Analysis models; * The properties and particularities of each model. In chapter 3, we present our literature survey on restrictions. Data Envelopment Analysis is a value-free frontier which has the of yielding more objective efficiency measures. However, the complete freedom in the determination of weights for the factors and products) relevant to the assessment of organisations has led to some problems such as: zero-weights and lack of discrimination between efficient organizations. Weight restriction methods were introduced in order to tackle these problems. The first part of chapter 3 in detail the motivations for weight restrictions while the second part presents the actual weight restriction rnethods.
  • Thumbnail Image
    Item
    Open Access
    A simulation study of the effect of target motion on sighting estimates of minke whale population density
    (1983) Basson, Marinelle; Butterworth, Doug S; Underhill, Leslie G
    Line transect methods used to estimate population density assume stationarity of targets. Violation of this assumption leads to overestimation of the true density. A simulation study based on a hazard-rate model is used to assess the resulting bias. The model is calibrated to generate sighting data resembling real data from minke whale sighting surveys. The procedure currently used to calculate a corrected negative exponential density estimate from sighting data is duplicated using simulated data. The resulting estimates are compared to the true population density determined by the simulation. Results reveal that in the case considered, the method of calculating the g(O) factor (which corrects for the fact that all animals on the trackline are not sighted) leads to a greater degree of overestimation than the effect of target motion at 3 knots. Shortcomings of the model are pointed out and possible improvements suggested. It is also suggested that further research be focused initially on the calculation of the g(O) correction factor rather than on effects of target motion.