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Squeaky Wheel Optimization (SWO)

Squeaky Wheel Optimization (SWO) is a nonsystematic search technique for solving a wide range of optimization problems. It is particularly well suited to problems with complex objective functions where high quality results are needed quickly. In squeaky wheel, a priority ordering of problem elements is used to quickly construct a solution by allocating resources first to high-priority tasks. That solution is then analyzed to find trouble spots—those elements that are not handled as well as they could be if they had their pick of resources. The priority of the problem elements is then increased, and the new priority ordering is used to construct a new solution, with the likely result that those elements will be handled better.

Squeaky wheel finds good solutions quickly by searching for effective priority orderings, rather than searching directly from solution to solution. This lets it avoid many of the problems that traditional search techniques often encounter. This lets SWO make large coherent jumps to quickly move out of unpromising regions of the search space. The construct-analyze-prioritize loop learns as it executes: Problem elements that are hard to handle well tend to rise in the priority queue, and elements that are easy to handle well tend to sink.

SWO has been used to achieve the best results known for aircraft assembly and fiber-optic cable manufacturing. It has also been employed in optimizing aircraft fleet utilization. A generalized version of SWO has been used in generic project management scheduling to minimize makespan and overload.