- Bessel function in Python: jn, yn, hankel1, hankel2. (link)
- Spherical Bessel functions in Python: sph_jn, sph_yn.
- These SciPy functions are unusual in two ways: they return values of the functions up to and including the specified order, and they return derivative values as well. For example, sph_jn(2, 3.4) returns a pair of arrays. The first array contains j0(3.4), j1(3.4), and j2(3.4) and the second array contains j'0(3.4), j'1(3.4), and j'2(3.4).