[SciPy-User] "Zero"-shape sparse matrices
Jaakko Luttinen
jaakko.luttinen@aalto...
Tue Feb 21 07:15:06 CST 2012
On 02/17/2012 05:32 PM, eat wrote:
> Hi,
>
> Perhaps a slightly OT (and I'm not really answering to your question), but
>
> On Thu, Feb 16, 2012 at 5:44 PM, Jaakko Luttinen
> <jaakko.luttinen@aalto.fi <mailto:jaakko.luttinen@aalto.fi>> wrote:
>
> Hi!
>
> To make a long story short, Scipy doesn't seem to allow sparse matrices
> that have length zero on any of the axes. For instance:
> C = numpy.ones((0,0))
> K = scipy.sparse.csc_matrix(C)
> ValueError: invalid shape
>
> It is possible to create a "zero"-shape dense matrix but not sparse.
> Why? To me, this seems like a bug.. Is it so?
>
> what would you expect a "zero"-shape sparse (or dense)
> matrix actually represent?
"Zero"-shape matrix would represent an empty matrix which has a correct
shape for some operations. This is very convenient for generic code
because I don't need to check if some dimension has zero length.
For instance:
- horizontal concatenation of (10,3), (10,2) and (10,0) shaped matrices
would work and produce a (10,5) shaped matrix.
- forming a block matrix from four matrices having shapes (0,0), (0,20),
(10,0) and (10,20) would produce a (10,20) matrix using numpy.bmat.
Regards,
Jaakko
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