Vector Slepian functions as developed by:
Plattner & Simons
Appl. Comput. Harm. Anal., 36 (1), 1–22, 2014, doi: 10.1016/j.acha.2012.12.001
which you may cite if you find any of these routines useful!
Research supported by NASA under grant NNX14AM29G.
Supported by the National Science Foundation under grant EAR-1550732.