Distributing Cython based extensions using LAPACK

Solution 1:

If I have understood the question correctly, you could make use of SciPy's Cython wrappers for BLAS and LAPACK routines. These wrappers are documented here:

• BLAS
• LAPACK

As the documentation states, you are responsible for checking that any arrays that you pass to these functions are aligned correctly for the Fortran routines. You can simply import and use these functions as needed in your .pyx file. For instance:

from scipy.linalg.cython_blas cimport dnrm2 
from scipy.linalg.cython_lapack cimport dgelsy 

Given that this is well-tested, widely-used code that runs on different platforms, I'd argue that it is a good candidate for reliably distributing Cython extensions that directly call BLAS and LAPACK routines.

If you do not want your code to have a dependency on the entirety of SciPy, you can find many of the relevant files for these wrapper functions in SciPy's linalg directory here. A useful reference is these lines of setup.py which list the source and header files. Note that a Fortran compiler is required!

In theory it should be possible to isolate only the source files here that are needed to compile the BLAS and LAPACK Cython wrappers and then bundle them as an independent extension with your module.

In practice this is very fiddly to do. The build process for the linalg submodule requires some Python functions to aid the compilation on different platforms (e.g. from here). Building also relies upon other C and Fortran source files (here), the paths of which are hard-coded into these Python functions.

Clearly a lot of work has gone into making sure that SciPy compiles properly on different operating systems and architectures.

I'm sure it is possible to do, but after shuffling files about and tweaking paths, I have not yet found the right way to build this part of the linalg submodule independently from the rest of SciPy. Should I find the correct way, I'll be sure to update this answer.