Definition:Convolution Integral/Cross-Correlation

Definition
Let $f$ and $g$ be real functions which are integrable.

The cross-correlation of $f$ and $g$ is defined as:
 * $\displaystyle \map f t \star \map g t = \int_{-\infty}^\infty \map f u \map g {t + u} \rd u$

Also known as
The operator $\map f t \star \map g t$ is sometimes referred to as pentagram notation.