A greedy randomised search heuristic for time-constrained vehicle scheduling and the incorporation of a learning strategy

In this paper, a greedy randomised heuristic is applied to a complex vehicle-scheduling problem with tight time windows and additional constraints. Two forms of adaptive search are identified, which are referred to as local and global adaptation. In both cases, the calculation of the greedy function is modified by an amount which measures heuristically the quality of the partial solution that is obtained when a decision is made. One use of global adaptation is an approach which is referred to as a learning strategy since it involves an attempt to learn from previous mistakes by an appropriate updating of the greedy function from one run of the heuristic to the next. Such a learning strategy forms the main focus of this paper. Experimental results show that it is potentially a powerful heuristic device, since it greatly enhanced the effectiveness of those methods that had previously been applied to this problem; that is, a greedy randomized heuristic which also incorporated a look-ahead strategy and a version of the well-known savings method. It is suggested that learning strategies of the general type introduced in this paper have potential for application to other combinatorial optimisation problems.