The Recursion occurs whenever something is defined in terms of itself. In the programming, a recursive function is a function which calls itself. The Recursion is very commonly used in the programming, however many simple illustrations are really not very efficient and can be substituted by the iterative techniques (loops, or vectorized code in MATLAB). Nontrivial illustrations go beyond the scope; therefore the concept of recursion is easily introduced here.
The illustration used will be of a factorial. Generally, the factorial of an integer n is defined iteratively:
n! = 1 * 2 * 3 * ... * n
For illustration, 4! = 1 * 2 * 3 * 4, or 24.
The other, recursive, definition is:
n! = n * (n - 1)! general case
1! = 1 base case