Browsing by Author "Stewart, T J"

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    Open Access
    Decision support for Foodbank South Africa
    (Operations Research Society of South Africa, 2014) Watson, N M; Stewart, T J; Scott, L
    This paper employs a combined 'soft-hard' OR approach to aid decision making in the area of allocation at a not-for-profit organization, Foodbank South Africa (FBSA), that represents the largest hunger-relief network in South Africa. Two problem-structuring tools, causal mapping and root definitions (RDs) are utilized. Causal mapping is used to identify areas for useful research within FBSA, and gain a greater understanding of the organization in terms of its goals and consequently a good appreciation of the context in which decisions are made. Root definitions are employed to acquire a better understanding of the 'decision-issues' within the allocation system at the Cape Town warehouse. A simulation model is developed to imitate daily allocation decisions, with the end-objective of assisting decision-making by developing a range of allocation policies. A decision support system (DSS) is developed to help FBSA manage their agency database, automate some of the daily allocation decisions and simulate allocation policies.
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    Open Access
    The essential multiobjectivity of linear programming
    (2007) Stewart, T J
    It is argued that any non-trivial real world problems involve multiple objectives. The simplistic approach of combining objectives in linear form can generate highly misleading and biased results, and is poor operational research practice. Such biases are illustrated by means of a simple example, and it is demonstrated that two simple approaches based on goal programming and piecewise linear value functions can largely resolve these problems. These methods require careful attention to problem structuring but are easily implemented by use of standard linear programming (LP) packages.