Definition:Bessel Function

Definition
The Bessel functions are solutions to Bessel's equation:
 * $x^2 \dfrac {\d^2 y} {\d x^2} + x \dfrac {\d y} {\d x} + \paren {x^2 - n^2} y = 0$

These solutions have two main classes:
 * the Bessel functions of the first kind $J_n$

and:
 * the Bessel functions of the second kind $Y_n$.

Also known as
Some sources use $p$ to denote the order of the Bessel function.