The Lommel differential equation, named after Eugen von Lommel, is an inhomogeneous form of the Bessel differential equation:
Solutions are given by the Lommel functions s<sub>ü,ý</sub>(z) and S<sub>ü,ý</sub>(z), introduced by ,
where J<sub>ý</sub>(z) is a Bessel function of the first kind and Y<sub>ý</sub>(z) a Bessel function of the second kind.
The s function can also be written as
where <sub>p</sub>F<sub>q</sub> is a generalized hypergeometric function.