** A more formal implementation that can be installed with pip:
https://github.com/weiliangjinca/grcwa


This code is modified from Victor Liu's S4 that was implemented in
C. It's now a python (works on both v2.7 and v3) code with AUTOGRAD
supported.  Most features in S4's rcwa.cpp are implemented.

Required package:
-- mpi4py for parallel
-- autograd for gradient
-- nlopt for optimization

If you find it useful for your research, please cite the following paper:
   @article{Jin2020,
     title = {Inverse design of lightweight broadband  reflector for efficient lightsail propulsion},
     author ={Jin, Weiliang and Li, Wei and Orenstein, Meir and Fan, Shanhui},
     year = {2020},
     journal = {arXiv:2005.04840},
   }