Simulation models are empirical; they are not mathematical in the way that models of operations research are mathematical formulas into which values are substituted to calculate the answer. The model in simulation is a quantitative representation of the behavioural characteristics, interactions, and intangible and nonlogical attributes of the entity under study. Further, in simulation it is possible to trace the activities as relationships and variables change. This is not true in the case of solving equations for an optimization objective. In fact, the simulation model is not used for optimization. It is basically a systematic trial-and-error approach to complex problems.