How to use numpy with OpenBLAS instead of Atlas in Ubuntu?

Question

I have looked for an easy way to install/compile Numpy with OpenBLAS but didn't find an easy answer. All the documentation I have seen takes too much knowledge as granted for someone like me who is not used to compile software. There are two packages in Ubuntu related to OpenBLAS : libopenblas-base and libopenblas-dev. Once they are installed, what should I do to install Numpy again with them? Thanks!

Note that when these OpenBLAS packages are installed, Numpy doesn't work anymore: it can't be imported: ImportError: /usr/lib/liblapack.so.3gf: undefined symbol: ATL_chemv. The problem occurs as well when installing Theano with their website instructions for Ubuntu.

This was noticed here already.

Answer 1

Run sudo update-alternatives --all and set liblapack.so.3gf to /usr/lib/lapack/liblapack.so.3gf

Answer 2

To add to the accepted answer (of using update-alternatives), the reason for this is because OpenBlas is not compatible with the Atlas version of Lapack. For each of the Blas and Lapack versions:

1. Default Blas + Default Lapack => OK
2. OpenBlas + Default Lapack => OK
3. Atlas-Blas + Default Lapack => OK
4. Atlas-Blas + Atlas-Lapack => OK
5. OpenBlas + Atlas-Lapack => ERROR! (The following case here.)

This is from both personal experience (with the exact same issue) and realizing why such a combination wasn't mentioned in this comparison blog.

By the way, you can just find the necessary files in /etc/alternatives/, usually with a filename starting with lib*. For each one do sudo update-alternatives --config <filename>. For example, do to following:

• sudo update-alternatives --config libblas.so
• sudo update-alternatives --config libblas.so.3

to change the Blas version.