# Definition:Product Notation (Algebra)/Infinite

(Redirected from Definition:Infinite Product)

## Definition

### Indexed Infinite Product

Let $\struct {S, \times}$ be an algebraic structure.

### Propositional Function

Let $\struct {S, \times}$ be an algebraic structure.

Let an infinite number of values of $j$ satisfy the propositional function $\map R j$.

Then the precise meaning of $\ds \prod_{\map R j} a_j$ is:

$\ds \prod_{\map R j} a_j = \paren {\lim_{n \mathop \to \infty} \prod_{\substack {\map R j \\ -n \mathop \le j \mathop < 0} } a_j} \times \paren {\lim_{n \mathop \to \infty} \prod_{\substack {\map R j \\ 0 \mathop \le j \mathop \le n} } a_j}$

provided that both limits exist.

If either limit does fail to exist, then the infinite product does not exist.

## Multiplicand

The set of elements $\set {a_j \in S: 1 \le j \le n, \map R j}$ is called the multiplicand.

## Notation

The sign $\ds \prod$ is called the product sign and is derived from the capital Greek letter $\Pi$, which is $\mathrm P$, the first letter of product.

## Historical Note

The originally investigation into the theory of infinite products was carried out by Leonhard Paul Euler.