A function is a relation from a set of inputs to a set of possible outputs where each input is related to exactly one output. This means that if the object x is in the set of inputs (called the domain) then a function f will map the object x to exactly one object y=f(x) in the set of possible outputs (called the codomain). Analogously, a function can be viewed as a machine whose row material is its input and the final product is output. In addition to f(x), other abbreviated symbols such as g(x) and P(x) are often used to represent functions of the independent variable x, especially when the nature of the function is unknown or unspecified.