squirrel235

Our results indicate that the NEH variants discovered by Links of London Necklaces programming are superior to the original NEH and its stochastic version on most of the problems investigated. This paper describes an approach in which a local search technique is alternated with a process which 'jumps' to another point in the search space. After each 'jump' a (time-intensive) local search is used to obtain a new local optimum. The focus of the paper is in monitoring the progress of this technique on a set of real world nurse rostering problems. We Links of London Rings a model for estimating the quality of this new local optimum. We can then decide whether to end the local search based on the predicted quality. The fact that we avoid searching these bad neighbourhoods enables us to reach better solutions in the same amount of time. We evaluate the approach on five highly constrained problems in nurse rostering. These problems represent complex and challenging real world rostering situations and the approach described here has been developed during a commercial implementation project by ORTEC bv.The solution space of the travelling salesman problem under 2-opt moves has been Links of London Sweetie Earrings as having a big-valley structure, in which the evaluation of a tour is positively correlated to the distance of the tour from the global optimum. We examine the big-valley hypothesis more closely and show that while the big-valley structure does appear in much of the solution space, it breaks down around local optima that have solutions whose evaluation is very close to that of the global optimum; multiple funnels appear around local optima with evaluations close to the global optimum. The appearance of multiple funnels explains why certain iterated local search heuristics can quickly find high-quality solutions, but Links of London T Charm to consistently find the global optimum. We then investigate a novel search operator, which is demonstrated to have the ability to escape funnels at evaluations close to the global optimum. The literature on foraging shows that some predators use a combination of ambush and active search to locate a prey.Links of London Charms