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In mathematics (in particular, functional analysis) convolution is a mathematical operation
on two functions (f and g) that produces a third function expressing
how the shape of one is modified by the other.

The term convolution refers to both the result function and to the process of computing it.
It is defined as the integral of the product of the two functions after one is reversed and shifted.

The convolution can be defined for functions on Euclidean space, and other groups.
For example, periodic functions, such as the discrete-time Fourier transform,
can be defined on a circle and convolved by periodic convolution.
(See row 18 at DTFT ยง Properties.)
A discrete convolution can be defined for functions on the set of integers.

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