Appears to be working, additional testing required. Generalizing to handle G&V and G&T correlation integrals remains

Very subtle problem with handling derivatives at zero density

clang on mac doesn't mind

Also test dipolar with JSON

The references seem to be getting broken. There must be an implicit copy somehow.

Added into the coeffs structure, nice interface

This gives access to multiple output parameters, for instance eta, needed for polar contributions

Refactoring of the SAFT contributions is going to be needed

Closing in with the models

Hours later...

Yet another battle with typing

* A fully encapsulated library wrapper with C++ interface

* Refactor types.hpp to hide the big headers in a macro conditional section

By adding the necessary Eigen header for real type of autodiff