Inversions using gradient vector Slepian functions (GVSF) as developed by:
Plattner & Simons
Geophys. J. Int., 2017, doi: 10.1093/gji/ggx244
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.