In mathematics, a Neumanns polynomial, introduced by Carl Neumann for the special case , is a polynomial in 1/z used to expand functions in term of Bessel functions.[1]
The first few polynomials are
A general form for the polynomial is
they have the generating function
where J are Bessel functions.
To expand a function f in form
for compute
where and c is the distance of the nearest singularity of from .
An example is the extension
or the more general Sonine formula[2]
where is Gegenbauer's polynomial. Then,
the confluent hypergeometric function
and in particular
the index shift formula
the Taylor expansion (addition formula)
(cf. [3]) and the expansion of the integral of the Bessel function
are of the same type.