[cctbxbb] Install OpenBLAS or MKL in base

[Luc Bourhis]

Nicholas,

> Please make sure that any new dependencies are optional, and that existing users can continue to use the existing code.  LSTBX is a fundamental component of CCTBX, and I wouldn't be keen on suddenly changing all the underlying implementations!

Yes, I had noticed it is used by xfel and by a few tests. Only the class non_linear_ls is used though, and that I did not optimise in my current attempt, that can be found on the branch reworked_fast_lstbx. I only optimised the L.S. I needed for smtbx, i.e. where the scale between model and data is unknown and needs to be fitted. The class is non_linear_ls_with_separable_scale_factor. So, right now, there is nothing to worry about as far as the smtbx is not concerned! Unless I missed something…

Would that be acceptable then, if we don’t touch the features of scitbx.lstbx used outside of smtbx? The thing is that keeping both BLAS 2 and 3 implementations significantly increased the complexity of it all. Moreover it makes some alternative solutions we are considering, like moving part of the code to Python, more difficult. So we would prefer to have the freedom to break code using non_linear_ls_with_separable_scale_factor.

> Also, we cannot include anything GPL in CCTBX.


Yes, sure. The discussion went on a tangent, sorry.

Best wishes,

Luc