Real life application of a function. Functions are very useful in mathematics because, they allow us to model real life problems into a mathematical format. For the denominator not to be zero, we need to avoid the numbers −3 and 5. Therefore, the domain is all real numbers except −3 and 5. Example 4.In Statgraphics, alas, the function that is called LOG is the natural log, while the base-10 logarithm function is LOG10. In the remainder of this section (and elsewhere on the site), both LOG and LN will be used to refer to the natural log function, for compatibility with Statgraphics notation.