Re: [Pysparse-users] transpose of matrix?

[Dominique O. <dom...@gm...>]

On Mon, Mar 8, 2010 at 7:12 PM, Bill Bruno <wb...@gm...> wrote:
> I used pysparse successfully; very pleased with performance!
>
> I really want to do SVD but I can emulate that by finding the
> spectrum of A^t A  and  A A^t.
>
> The first is easy using dot, but how do I get the second.
> I would have thought there would be a built-in transpose.
> Should I write my own at low level or convert to another
> format that supports transpose?

Hi Bill,

Thanks for using Pysparse! It is true that there is no formal
transposition operation in Pysparse. That is because often times, in
sparse matrix computations, there are ways to get rid of the
transpose. In your case, note that the eigenvalues of A^T * A and
those of A * A^T are the same (a real matrix and its transpose have
the same eigenvalues). So, there's no need to compute the second one.

That being said, it might be good to have a formal transposition
operation. If you would like to have a go at that, it is surely easier
to start with the Python PysparseMatrix class rather than the
low-level ll_mat objects.

Cheers,

-- 
Dominique