[SciPy-User] Why doesn't dot product transpose?

[Jason Rennie]

On Sat, Apr 23, 2011 at 1:19 PM, RJ Nowling <rnowling at gmail.com> wrote:

> As you pointed out, the simple answer is to use 1D arrays.  We are
> using sparse matrices and want to perform dot products on the column
> vectors of those matrices.  When I use csc_matrix.getcol() or
> matrix[:,1] syntax, a sparse 2D array is returned with shape (n, 1).
> It seems that my approach is getting the proper data structures for
> the dot product, as you pointed out.
>

The problem is that sparse matrices are just that, *matrices*.  AFAIK, there
is no general sparse array structure.  So, you may need to switch from
sparse to dense if you want shape=(n,) arrays.  You can easily change
(dense) shapes with numpy.reshape().


> So, what's the correct way of getting a sparse shape (n,) column
> vector from a matrix?  (E.g., we don't want to perform unnecessary
> operations by converting to dense representations.)
>

You can't AFAIK.  What are you trying to do?

Jason

-- 
Jason Rennie
Research Scientist, ITA Software
617-714-2645
http://www.itasoftware.com/
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