Why initial conditions are important

Most simulation textbooks assume that a model can be started in an empty state and the final output will not be affected, so long as the "warm-up period" is excluded from the analysis. In this paper we test this assumption, using a discrete-event model of a existing manufacturing facility. Using a series of model runs with no initial Work in Progress (WIP) and another series of simulation runs with a realistic initial level of WIP, the results can be compared and contrasted. While the results show similar shaped profiles in terms of throughput and lead time, the differences between the curves has important practical implications.