Preemptive multiprocessor order scheduling to minimize total weighted flowtime
Consider m identical machines in parallel, each of which can produce k different product types. There is no setup cost when the machines switch from producing one product type to another. There are n orders each of which requests various quantities of the different product types. All orders are available for processing at time tÂ =Â 0, and preemption is allowed. Order i has a weight wi and its completion time is the time when its last requested product type finishes. Our goal is to find a preemptive schedule such that the total weighted completion time [summation operator]wiCi is minimized. We show that this problem is NP-hard even when all jobs have identical weights and there are only two machines. Motivated by the computational complexity of the problem, we propose a simple heuristic and show that it obeys a worst-case bound of 2Â -Â 1/m. Finally, empirical studies show that our heuristic performs very well when compared with a lower bound of the optimal cost.
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