Definition:Generating Function

Definition
Let $A = \sequence {a_n}$ be a sequence in $\R$.

Then $\ds \map {G_A} z = \sum_{n \mathop \ge 0} a_n z^n$ is called the generating function for the sequence $A$.

The mapping $\map {G_A} z$ is defined for all $z$ for which the power series $\ds \sum_{n \mathop \ge 0} a_n z^n$ is convergent.

The definition can be modified so that the lower limit of the summation is $b$ where $b > 0$ by assigning $a_k = 0$ where $0 \le k < b$.

Also denoted as
When the sequence is understood, $\map G z$ can be used.

Different authors may use different symbols.