Modelling and Solving Fleet Assignment in a Flexible Environment

This paper reports on the modelling and solution of a large industrial combinatorial optimization problem using the ECL i PS e Constraint Logic Programming (CLP) platform. The problem is eet assignment: the assignment of a set of aircraft of diierent types to a predeened shedule of ights. A single underlying model was developed and solved in ECL i PS e. Three optimization methods were applied in three stages of model development and solution. The three methods were used to meet diierent objectives. The rst was depth rst search branch and bound optimization in conjunction with Finite Domain propagation. This straightforward approach was used to develop and validate the model in the ECL i PS e platform. The second was mixed integer programming. The CLP model and solutions were exported to a mathematical solver and used to produce a globally optimal solution. Knowing the optimal solution is desirable, however obtaining good solutions close to the user's actual assignment is more useful in practice. The third method used a repair-based extension of the rst approach, and obtained high quality solutions close to the user's assignment. This multistage devolopment process resulted in the end user commissioning the development of an ECL i PS e-based application combining repair with Finite Domain propagation, with the purpose of improving their day to day eet assignment process. The exercise clearly reveals the exibility of the ECL i PS e platform in mapping a single model to diierent problem solving approaches, and illustrates how this exibility has important practical beneets.