Most system dynamics models are made up entirely of continuously formulated stocks and flows. For most problems that deal with aggregate structures this is perfectly appropriate. Adding up a large number of discrete activities typically gives you something that is as easily approximated by a continuous formulation as it could be by a discrete formulation. Still, there are situations where it is simply easier to make use of discrete formulation and Vensim has a number of functions that can help do this.
This Chapter is really just a series of examples on how Vensim’s discrete functions can be used to represent different processes. The purpose is basically to provide some useful how to material for creating your own models. This is also the purpose of the Molecules.
The only discrete function supported in Vensim PLE and PLE Plus is DELAY FIXED.