Simulation speed is fast, the optimization capabilities are powerful. Vensim has a large number of built in functions, but these are not always enough. Suppose, for example, you would like to allocate production among different facilities at each time in a simulation. If the best way to do this is to use a Linear Program, then an external function can be constructed to do this. Compiled simulation is a technique for speeding up simulation.
Fast simulation is especially important for optimization.
Optimization can be used in several ways in Vensim. For example, you might optimize multiple parameters such as worker numbers, capital spending, etc., to maximize profit while minimizing production time, and all constrained by certain limits. Optimization is performed using a modified Powell hill climbing algorithm. We have experimented extensively with genetic algorithm optimization and found that the results are very poor. We will be making it easier to add in alternative search algorithms in the future for people who want to pursue this line of research.