[FEATURE] Add support for BLAS and LAPACK libraries discovery

[ccoulombe]

Please add support for discovering BLAS and LAPACK libraries through cmake mechanisms.

We use Flexiblas and this is supported through -DBLA_VENDOR (https://cmake.org/cmake/help/latest/module/FindBLAS.html)

By asking CMake to find required libraries, this add flexibity and avoid custom patching of CMakeLists.txt

[atztogo]

I am not very familiar with cmake. Do you have anything in your mind how to modify the phono3py setup system?

[LecrisUT]

Note, FlexiBLAS does not support Lapacke. Other than that you can pass BLA_VENDOR as a environment variable during the pip install.

@atztogo I think one solution would be to conditionally use lapacke interface and if not found default to the original ones. But it's been quite some time since I looked into the difference between those, I could use some help explaining the differences.

[atztogo]

I think one solution would be to conditionally use lapacke interface and if not found default to the original ones.

@LecrisUT, what do you mean the original ones?

[LecrisUT]

I think one solution would be to conditionally use lapacke interface and if not found default to the original ones.

@LecrisUT, what do you mean the original ones?

Linking against the fortran interface or bundle the (relevant part of) lapacke library statically.

[atztogo]

I am planning to release a new version of phono3py that can eliminate the dependency on BLAS and LAPACK(E) in C. This means there is no need to link these libraries during compilation. For more details, see #301. Instead, scipy will be required.

[ccoulombe]

Note, FlexiBLAS does not support Lapacke. Other than that you can pass BLA_VENDOR as a environment variable during the pip install.

Note that in our installation of FlexiBLAS, we also installed lapacke, but this is not the default FlexiBLAS installation.

@atztogo When do you plan on releasing a version with scipy ? In many cases, scipy and numpy will be built+linked with MKL or Flexiblas, this should still show nice performance I believe.

[atztogo]

@ccoulombe, it has been released as experimental support. For more details, please refer to: https://phonopy.github.io/phono3py/install.html#building-without-linking-lapacke .

[atztogo]

@ccoulombe, please try the latest phono3py release. Now the compilation without direct linking BLAS and LAPACK libraries is the default setting.

[ccoulombe]

This built and seems to work properly. It would still be nice to add support for the libraries discovery, but less important now that it can use numpy/scipy which are in turn linked on desired librairies.