The population model presented in the previous chapter is a simple model that uses only multiplication and division in its equations. While addition, subtraction, multiplication and division are the most common components of equations, sometimes it is necessary to use different types of relationships. Vensim has a number of functions that can be used in equations and in this Chapter we will work through the process of adding these functions to equations. In the next chapter we will cover Lookup functions which allow you to specify functional relationships by drawing a curve.
In addition to exploring the use of functions in this chapter we will look at how to deal with what are called "Floating Point Errors." These are errors that occur when the numbers in a model get too big, there is a division by zero, or a function is given an argument that is out of range.
A completed example of the model is provided for reference; see price1.mdl, price2.mdl and price3.mdl located in the directory UserGuide\chap07\Complete.
