4: Functions

A function is generally defined as a relation in which each \(x\) value corresponds to one and only one \(y\) value. This assigning of only one \(y\) value to each \(x\) is known as "univalence." The univalence requirement makes some manipulations in calculus easier to work with and can be important in certain applications, but many important relations (such as the hyperbola, circle and ellipse) are not univalent and thus not functions.

A function typically describes a relationship between two sets. In our consideration of functions these two sets will typically be real or complex numbers. Functions are usually defined in one of several ways. They can be defined by a graph, (2) an algebraic relationship,
(3) a rule or (4) a table of values. More than one of these methods can be used to describe the same function.

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