Find out if/which BLAS library is used by Numpy
numpy.show_config()
doesn't always give reliable information. For example, if I apt-get install python-numpy
on Ubuntu 14.04, the output of np.show_config()
looks like this:
blas_info:
libraries = ['blas']
library_dirs = ['/usr/lib']
language = f77
lapack_info:
libraries = ['lapack']
library_dirs = ['/usr/lib']
language = f77
atlas_threads_info:
NOT AVAILABLE
blas_opt_info:
libraries = ['blas']
library_dirs = ['/usr/lib']
language = f77
define_macros = [('NO_ATLAS_INFO', 1)]
atlas_blas_threads_info:
NOT AVAILABLE
openblas_info:
NOT AVAILABLE
lapack_opt_info:
libraries = ['lapack', 'blas']
library_dirs = ['/usr/lib']
language = f77
define_macros = [('NO_ATLAS_INFO', 1)]
...
It looks as though numpy is using the standard CBLAS library. However, I know for a fact that numpy is using OpenBLAS, which I installed via the libopenblas-dev
package.
The most definitive way to check on *nix is to use ldd
to find out which shared libraries numpy links against at runtime (I don't own a Mac, but I think you can use otool -L
in place of ldd
).
For versions of numpy older than v1.10:
~$ ldd /<path_to_site-packages>/numpy/core/_dotblas.so
If
_dotblas.so
doesn't exist, this probably means that numpy failed to detect any BLAS libraries when it was originally compiled, in which case it simply doesn't build any of the BLAS-dependent components.For numpy v1.10 and newer:
_dotblas.so
has been removed, but you can check the dependencies ofmultiarray.so
instead:~$ ldd /<path_to_site-packages>/numpy/core/multiarray.so
Looking at the version of numpy I installed via apt-get
:
~$ ldd /usr/lib/python2.7/dist-packages/numpy/core/_dotblas.so
linux-vdso.so.1 => (0x00007fff12db8000)
libblas.so.3 => /usr/lib/libblas.so.3 (0x00007fce7b028000)
libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007fce7ac60000)
libm.so.6 => /lib/x86_64-linux-gnu/libm.so.6 (0x00007fce7a958000)
libpthread.so.0 => /lib/x86_64-linux-gnu/libpthread.so.0 (0x00007fce7a738000)
/lib64/ld-linux-x86-64.so.2 (0x00007fce7ca40000)
/usr/lib/libblas.so.3
is actually the start of a chain of symlinks. If I follow them to their ultimate target using readlink -e
, I see that they point to my OpenBLAS shared library:
~$ readlink -e /usr/lib/libblas.so.3
/usr/lib/openblas-base/libblas.so.3
numpy.show_config() just tells that info is not available on my Debian Linux.
However /usr/lib/python3/dist-packages/scipy/lib has a subdirectory for blas which may tell you what you want. There are a couple of test programs for BLAS in subdirectory tests.
Hope this helps.