The first coding has ended and I'm happy to say my pull request is nearly complete. I'm waiting for mentors to review the code, then I'll fix any remaining issues.
Here's a quick summary of the new code:
jakob2019 was created as a part of colour.recovery.RGB_to_sd_Jakob2019, which turns colors (from any RGB space supported by Colour) to a spectral distribution.find_coefficients, can be used if only the model parameters are needed. It's where the entire optimization algorithm takes place.error_function, the function minimized during optimization. It also returns its own gradient (derivatives of the function value with respect to its inputs) to aid numerical algorithms. This required analytically differentiating all the intermediate steps.Jakob2019Interpolator class can be used to work with precomputed tables. It can read and write the article's authors' .coeff files and also generate new ones.