External Functions

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In addition to the variety of built in functions, you can also make use of external functions in Vensim.  External functions allow you to define arbitrary computations that can be made of Vensim model variables during a simulation.  Vensim passes the external functions values, and the external function uses those values, possibly modifying them, and then returns a value.

This chapter:

Gives an overview of how external functions work.
Describes how to define an external function.
Describes how to call external functions.
Discusses the use of External Functions in Compiled Simulations
Discusses some implementation issues.


NOTE The documentation will regularly refer to DLL files. On the Macintosh these are called Dynamically Linked Libraries and have extension .dylib not .dll. Other than that, at the level of detail presented in this chapter, their behavior is identical.