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. The external function is written in a programming language (usually C or C++) and then compiled into a dynamic link library (DLL) which is loaded by Vensim.
Posted in: Advanced Features