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

Need to decide on how to handle the model composition with the chain models

Refactoring of the SAFT contributions is going to be needed

And some tests

Can also specify them as JSON-formatted string, to make fitting a bit easier, for instance

Typo in Thorade for dp/drho|T, missing factor of 2

Closing in

Everything seems pretty promising aside from the mutant, which requires additional thought. How can we store the mutant in AllowedModels

Very fast in C++ (less than a microsecond for 4 outputs in the Jacobian), but 10 microseconds in Python for 2. Need to find a way to make it closer to original speed. Perhaps pass in a buffer to be populated.  That should allow the copy to be avoided. It must be the Eigen arrays that are so slow.

See #21

Wicked fast, see benchmark file added in this commit:

-------------------------------------------------------------------------------
multifluid derivatives
-------------------------------------------------------------------------------
/Users/ihb/Documents/Code/teqp/src/bench_derivbox.cpp:37
...............................................................................

benchmark name                       samples       iterations    estimated
                                     mean          low mean      high mean
                                     std dev       low std dev   high std dev
-------------------------------------------------------------------------------
alphar                                         100           140      1.652 ms 
                                        117.036 ns    116.863 ns    117.654 ns 
                                        1.48691 ns   0.425603 ns    3.42119 ns 
                                                                               
All residual derivatives needed for                                            
first derivatives of h,s,u,p w.r.t.                                            
T&rho                                          100            29     1.6849 ms 
                                        579.424 ns    575.931 ns    593.892 ns 
                                        30.0729 ns    2.63483 ns    69.5014 ns 
                                                                               
All ideal-gas derivatives needed                                               
for first derivatives of h,s,u,p w.                                            
r.t. T&rho                                     100            72     1.6416 ms 
                                        226.557 ns    226.297 ns    227.014 ns 
                                        1.70744 ns    1.13538 ns    3.15493 ns 
                                                                               

===============================================================================

Closes https://github.com/usnistgov/teqp/issues/15

* Adding the 2-Center Lennard-Jones model developed by Mecke and the revised version of Lisal

* Added dipolar and quadrupolar contributions to 2CLJF model

Add conversion routines for ideal-gas Helmholtz terms from CoolProp format

Yet another forceeval

Add routine for TP flash for binary mixture, to solve for molar concentrations (and therefore mole fractions)

Found the first real bug in autodiff: https://github.com/autodiff/autodiff/issues/242

And add test