This will later allow us to use celerite2 with PyMC3 fitters/models, and also fixes some annoying bugs caused by celerite. I also added a test of the GP model to the NIRSpec lsq fitting test to get some more coverage of the code. Finally, I also switched the default lsq fitter to Powell instead of Nelder-Mead since I have indeed found that Powell is more performant.
This RP resolves #608
This will later allow us to use celerite2 with PyMC3 fitters/models, and also fixes some annoying bugs caused by celerite. I also added a test of the GP model to the NIRSpec lsq fitting test to get some more coverage of the code. Finally, I also switched the default lsq fitter to Powell instead of Nelder-Mead since I have indeed found that Powell is more performant.