GitHub - polarch/Spherical-Harmonic-Transform: A collection of MATLAB routines for the Spherical Harmonic Transform and related manipulations in the spherical harmonic spectrum.
Spherical harmonics » Chebfun
Spherical Harmonic -- from Wolfram MathWorld
Harmonic Functions: Why They're Nifty – notes to self
PDF] A fast spherical harmonics transform algorithm | Semantic Scholar