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

"V. Armando Solé" sole@esrf...
Mon Feb 18 10:26:50 CST 2013

Hi Sergio,

I faced a similar problem one year ago. I solved it writing a C function 
receiving a pointer to the relevant linear algebra routine I needed.

Numpy does not offers the direct access to the underlying library 
functions, but scipy does it:

from scipy.linalg.blas import fblas
dgemm = fblas.dgemm._cpointer
sgemm = fblas.sgemm._cpointer

So I wrote a small extension receiving the data to operate with and the 
relevant pointer.

The drawback of the approach is the dependency on scipy but it works nicely.


On 18/02/2013 16:38, Sergio Callegari 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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