"In mathematics, a function is a mapping from a set of inputs to a set of outputs such that each input is mapped to exactly one output. For example, the function f ( x ) = x 2 maps numeric values to their squares. The input is a variable x . When we assign an actual value to x and evaluate the function, then the function has a value, its output. For example, setting x = 2 as input, the output would be 2 2 = 4. Mathematical functions can have multiple inputs, f ( x, y ) = x 2 + y 2 f ( x, y, z ) = 2 x + 3 y − 4 z However, a function will only ever have a single output value."