ABSTRACT
This chapter discusses the relationships between variables. In practice, the true relationships between quantities such as depth and temperature are usually so complex that they must be approximated by much simpler ones. The chapter introduces the most common of these simple relationships starting with the most simple and common of all, the straight line function. The straight line equation is possibly the most important mathematical expression found in geology since a very large range of geological problems can be approximated using straight line functions. The trade-off between accuracy and simplicity is a frequent occurrence when applying mathematics to specific problems. The straight line functions and quadratic functions are special cases of polynomial functions. The functions can be made yet more general by the addition of negative powers. Polynomial functions and their extensions are extremely versatile and can be used to describe many situations.
