Source: /cirosantilli/bessel-function

= Bessel function
{wiki}

Shows up when trying to solve <2D wave equation on a circular domain> in <polar coordinates> with <separation of variables>, where we have to decompose the initial condition in termes of a <fourier-Bessel series>, exactly like the <Fourier series> appears when solving the wave equation in linear coordinates.

For the same fundamental reasons, also appears when calculating the <Schrödinger equation solution for the hydrogen atom>.