Introduction to the Special Issue: Evolutionary Algorithms for Scheduling

David Montana
1998 Evolutionary Computation  
Scheduling is a problem that occurs in a large variety of forms with huge cumulative economic and social consequences. Proper scheduling can provide better utilization of scarce and expensive resources as well as higher satisfaction for individuals such as customers and employees. For this reason, there has been a lot of effort expended over a large number of years on algorithms for automatic scheduling. However, except for a few isolated successes on some specialized problems, automatic
more » ... ing remains an open problem. There are a few reasons why scheduling is such a difficult problem. One is the size and complexity of the search space. For the generic problem of assigning N tasks to M resources with a particular ordering of tasks at each resource, the number of possible solutions is superexponential growth as a function of the number of tasks and resources. In addition to sheer size, this search space has a more complex topology than a Euclidean space or, when M > 1, a space of permutations. A second reason why scheduling is a difficult problem is that scheduling is an inherently dynamic process. Schedules only remain valid for a limited amount of time. After a certain duration, the world generally has changed enough that the scheduling algorithm has to find a different schedule. The required update time varies greatly between applications, as illustrated by the following sample update time scales: • milliseconds for scheduling computational tasks on one or more CPUs • minutes for scheduling service calls • weeks for scheduling commercial airline flights In all cases, there are time constraints on how long it can take to schedule and reschedule that place limits on the amount of computation performed by a scheduling algorithm. A third factor making scheduling difficult is that different domains and applications require solutions of different variations of the scheduling problem. These variations arise from a number of different sources including • differences in the types of hard constraints, such as relative and absolute temporal restrictions and resource capabilities constraints • the need for additional information beyond an ordered assignment of tasks to resources, such as absolute times, routes traveled, and manufacturing plans 1
doi:10.1162/evco.1998.6.1.v pmid:10021737 fatcat:dkverwunxnbephpponfeldna2y