[Numpy-discussion] numarray cholesky solver ?

[Travis Oliphant]

Piotr Luszczek wrote:

> Hi all,
>
> the Cholesky routine that's been mentioned (dpotrs) is from LAPACK (I
> apologize if every body knows that).
>
> I'm on the LAPACK team right now and we were wondering if we should
> provide bindings for Python. It is almost trivial to do with Pyrex.
> But Numeric and numarray already have some functionality in it.
> Also, I don't know about popularity of PyLapack.

Scipy already has extensive bindings for LAPACK.    There is even a lot 
of development that has been done for c-compiled bindings.

Right now, scipy_core is being developed to be a single replacement for 
Numeric/numarray.   Lapack bindings are a huge part of that effort.  
But, as I said, the work has been done (using f2py).  The biggest issue 
is supporting f2c'd versions of Lapack so that folks without Fortran 
compilers can still install it.    scipy_core will allow this.  Again, 
most of the effort is accomplished through f2py and scipy_distutils 
which are really good tools. 

Pyrex is nice, but f2py is really, really nice (it even supports 
wrapping basic c-code).

>
> So my question is if there is a need for the specialized LAPACK
> routines. And if so, which API it should use (Numeric, numarray,
> Numeric3, scipy_core, standard array, minimum standard array 
> implementation
> or array protocol meta info).

I think if LAPACK were going to go through the trouble, it would be best 
for LAPACK to provide "array protocol" style wrappers.   That way any 
Python array user could take advantage of them.  

While current scipy users and future scipy_core users do not need 
LAPACK-provided Python wrappers, we would welcome any native support by 
the LAPACK team.   Again, though, I think this should be done through 
the array_protocol API.   A C-API is likely in the near future as well 
(which will provide a little speed up for many small arrays).

-Travis


-Travis