ORiON - latest Issue
Volume 32, Issue 2, 2016
Author Stephan VisagieSource: ORiON 32, pp i –ii (2016)More Less
This year is speeding towards its end. The activity in the Operations Research Society of South Africa is reflected in the diverse papers that usually fills ORiON. This issue is no exception. The topics of blending problems, workforce-mix problems as well as the ranking of schools in South Africa are covered in this issue.
Source: ORiON 32, pp 79 –104 (2016) http://dx.doi.org/10.5784/32-2-520More Less
In this paper a comparison of classical metaheuristic techniques over different sizes of petrochemical blending problems is presented. Three problems are taken from the literature and used for initial comparisons and parameter setting. A fourth instance of real world size is then introduced and the best performing algorithm of each type is then applied to it. Random search techniques, such as blind random search and local random search, deliver fair results for the smaller instances. Within the class of genetic algorithms the best results for all three problems were obtained using ranked fitness assignment with tournament selection. Good results are also obtained by means of continuous tabu search approaches. A simulated annealing approach also yielded fair results. Comparisons of the results for the different approaches shows that the tabu search technique delivers the best results with respect to solution quality and execution time for all of the three smaller problems under consideration. However, simulated annealing delivers the best result with respect to solution quality and execution time for the introduced real world size problem.
Author V.U. EkhosuehiSource: ORiON 32, pp 105 –122 (2016) http://dx.doi.org/10.5784/32-2-534More Less
This paper focuses on a manpower system with a fixed number of jobs that uses both permanent and temporary staff. The dynamics of workforce-mix in such a system is modelled as an optimal control problem. The objective is to find the most economical workforce-mix for the manpower system, subject to the fluctuations in workforce caused by wastage and the hiring of temporary staff. The fluctuations in the workforce-mix are modelled using a model similar to the Vidale-Wolfe advertising model. The solution is found by applying Pontryagin's principle, and a number of resulting propositions are presented along with their proofs. A real-life manpower setting is used to illustrate the utility of the model.
Source: ORiON 32, pp 123 –146 (2016) http://dx.doi.org/10.5784/32-2-570More Less
The education system in South Africa finds itself in a dismal position. Existing research reports and general news bulletins suggest that schools in South Africa suffer from a general lack of efficiency measures and therefore underperform in comparison with those in other countries. This paper proposes a class-ranking technique as a means to evaluate schools. The technique implements Pareto optimality principles and utilises a mathematical model that is based on output variables (e.g. pass rates) only. The model also provides for the construction of a step-by-step improvement plan for underperforming schools. The suggested framework was applied to 54 secondary schools in one of the four major municipal districts in the North West province of South Africa. Results are contrasted with the application of an ordinary DEA model that is based on input and output variables and showed that the suggested approach offers a more reliable alternative to evaluate, monitor and improve the performance of schools ranked as inefficient.