[Numpy-discussion] Windows, blas, atlas and dlls

rif rif@google....
Mon Feb 18 10:26:19 CST 2013

I have no answer to the question, but I was curious as to why directly
calling the cblas would be 10x-20x slower in the first place.  That seems
surprising, although I'm just learning about python numerics.

On Mon, Feb 18, 2013 at 7:38 AM, Sergio Callegari <
sergio.callegari@gmail.com> wrote:

> Hi,
> I have a project that includes a cython script which in turn does some
> direct
> access to a couple of cblas functions. This is necessary, since some matrix
> multiplications need to be done inside a tight loop that gets called
> thousands
> of times. Speedup wrt calling scipy.linalg.blas.cblas routines is 10x to
> 20x.
> Now, all this is very nice on linux where the setup script can assure that
> the
> cython code gets linked with the atlas dynamic library, which is the same
> library that numpy and scipy link to on this platform.
> However, I now have trouble in providing easy ways to use my project in
> windows. All the free windows distros for scientific python that I have
> looked at (python(x,y) and winpython) seem to repackage the windows
> version of
> numpy/scipy as it is built in the numpy/scipy development sites. These
> appear
> to statically link atlas inside some pyd files.  So I get no atlas to link
> against, and I have to ship an additional pre-built atlas with my project.
> All this seems somehow inconvenient.
> In the end, when my code runs, due to static linking I get 3 replicas of 2
> slightly different atlas libs in memory. One coming with _dotblas.pyd in
> numpy,
> another one with cblas.pyd or fblas.pyd in scipy. And the last one as the
> one
> shipped in my code.
> Would it be possible to have a win distro of scipy which provides some
> pre built atlas dlls, and to have numpy and scipy dynamically link to them?
> This would save memory and also provide a decent blas to link to for things
> done in cython. But I believe there must be some problem since the scipy
> site
> says
> "IMPORTANT: NumPy and SciPy in Windows can currently only make use of
> CBLAS and
> LAPACK as static libraries - DLLs are not supported."
> Can someone please explain why or link to an explanation?
> Unfortunately, not having a good, prebuilt and cheap blas implementation in
> windows is really striking me as a severe limitation, since you loose the
> ability to prototype in python/scipy and then move to C or Cython the major
> bottlenecks to achieve speed.
> Many thanks in advance!
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