Browsing by Author "Scholtz, Esmarie"

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    A comparative study on the value of accounting for possible relationships between decision variables when solving multi-objective problems
    (Stellenbosch : Stellenbosch University, 2014-04) Scholtz, Esmarie; Bekker, James F.; Stellenbosch University. Faculty of Engineering. Dept. of Industrial Engineering.
    ENGLISH ABSTRACT: The cross-entropy method for multi-objective optimisation (MOO CEM) was recently introduced by Bekker & Aldrich (2010) and Bekker (2012). Results presented by both show great promise. The MOO CEM assumes that decision variables are independent. As a consequence, the question arises: under which circumstances would an algorithm that accounts for relationships between decision variables outperform the MOO CEM? Two algorithms reported to account for relationships between decision variables, the multi-objective covariance matrix adaptation evolution strategy (MOCMA- ES) and Pareto di erential evolution (PDE), are selected for comparison. In addition, two hybrid algorithms (Hybrid 1 and Hybrid 2) based on the MOO CEM are created. These ve algorithms are applied to a set of 46 continuous problems, six instances of the mission-ready resource (MRR) problem, and three instances of a dynamic, stochastic bu er allocation problem (BAP). Performance is measured using the hypervolume indicator and Mann-Whitney U-tests. One of the primary ndings is that accounting for relationships between decision variables is bene cial when solving small to medium-sized problems. In these cases, the MO-CMA-ES typically outperforms the other algorithms. However, on large problems, Hybrid 1 and the MOO CEM typically perform best.
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    Multi-objective optimisation in the retail banking industry with stochastic discrete-event simulation
    (Stellenbosch : Stellenbosch University, 2011-12) Scholtz, Esmarie; Bekker, James; Stellenbosch University. Faculty of Engineering. Dept. of Industrial Engineering.
    ENGLISH ABSTRACT: Cash management is a multi-objective optimisation problem which aims to maximise the service level provided to customers at minimum cost. The topic of du Toit's (2011) masters thesis was automated teller machice (ATM) cash management for a specific South African retail bank. Focus was placed on an ATM network which primarily provides cash to blue collar laborers in the rural Eastern Cape. The aim of this final year project is to refine the work done by du Toit through the specific investigation into the effect of applying a combination of the vehicle routing problem (VRP) and continuous review policy for inventory management to the retail banking industry. A decision support system (DSS) in the form of a stochastic, discrete-event simulation model is developed. 90 different scenarios are experimented with using the DSS. Results show that the application of the VRP consistently yields high service levels at low cost when compared to two other routing approaches: first-in- first-out routing and direct replenishment. It is concluded that use of the VRP is especially beneficial when the bank has substantial control over transportation cost. The principal recommendation is therefore that cost control should be maximised to fully exploit the advantages obtainable from effective cash management. Finally, it is argued that the benefits to be gained from effective cash management (higher service levels at lower cost) can lead to the improvement of the lives of many a South African wage earner. These benefits could also lead to an increased profit margin - life is all about choices.