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Resource constrained project scheduling with time windows: A branching scheme based on dynamic release dates

Fest, Andreas; Möhring, Rolf H.; Stork, Frederik; Uetz, Marc

Inst. Mathematik

We propose a branch-and-bound algorithm for resource-constrained project scheduling where any two of jobs can be linked by arbitrary minimal and maximal time lags. The jobs have to be scheduled non-preemptively, and while in process, they require several limited resources. The objective is to find a feasible schedule which minimizes the project makespan. Different branch-and-bound algorithms have been previously proposed - either based on constraint propagation techniques, or based on the idea to branch over so-called resource conflicts which are resolved by introducing additional precedence constraints. Our approach also follows the latter principle. The new idea is to resolve resource conflicts only locally by a dynamic update of job release dates instead of introducing precedence constraints. This gives rise to a reduction of both computation time and memory requirements in every node of the enumeration tree, however, at the expense of a loss of information. Nevertheless, enriched by preprocessing, strong dominance rules, and a flexible search strategy, our computational results show that the algorithm performs better than previous branch-and-bound algorithms, and is competitive with a very recent constraint propagation approach as well as tailor-made heuristics, also for large-scale instances.