Question about implementing features using third-party libraries

[jimustafa]

Hello @wannier-developers. I have started and made a lot of progress towards implementing the optimized projection functions method (OPFM) [1, 2] within wannier90. This approach uses matrix codiagonalization, as described in the papers referenced. In parallel, I am developing a codiagonalization library in Fortran. My question is whether it is OK to make use of the library routines through linking, or is it preferable to vendor the entire library within wannier90. My thinking, and the work so far, is to link the library and have the OPFM implementation behind a CODIAG flag.

[JeromeCCP9]

Hello!
I suppose the key question is whether the code is to be maintained as part of the wannier90 codebase or to be hosted apart and linked by Wannier90? My feeling would be the second, because you can manage it better and wannier90 gets it via a git subproject or via some build configuration.
Would you like to comment: how specific is your code to wannier90? If wannier90 is only possible point of use, or if you need lots of wannier90 internals, etc, then this would steer it in the other direction, I suppose?

[jimustafa]

The OPFM code will be maintained as part of wannier90, implemented through a new wann_main_opfm routine called when opfm=.true.. The numerical core (the matrix codiagonalization routines) will live in a separate codiag library with no dependency on wannier90 internals (it operates on plain arrays, not wannier90 types), so it can be maintained and used independently. When wannier90 is built and linked against codiag, OPFM becomes an available wannierization method.