Bessel function

Bessel functions are solutions of "Bessel's differential equation"

x²y'' + xy' + (x² - n²)y = 0

for non-negative values of n.

They come in two kinds:

• Bessel functions of the first kind
• Bessel functions of the second kind

They are important in many physical problems inclding those involving spherical or [cylindrical coordinates]?, and in frequency modulation.