[SciPy-User] "Zero"-shape sparse matrices

Warren Weckesser warren.weckesser@enthought....
Tue Feb 21 09:00:44 CST 2012

On Tue, Feb 21, 2012 at 7:23 AM, Jaakko Luttinen

> On 02/17/2012 06:48 PM, Christopher Mutel wrote:
> > On Fri, Feb 17, 2012 at 4:32 PM, eat <e.antero.tammi@gmail.com> wrote:
> >> On Thu, Feb 16, 2012 at 5:44 PM, Jaakko Luttinen <
> jaakko.luttinen@aalto.fi>
> >> wrote:
> >>> 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?
> >
> > I am not an expert, but it is my understanding that the sparse matrix
> > implementations in SciPy assume precisely two dimensions. One
> > dimension having a size of 0 would break all the assumptions of this
> > code. The NumPy array class is a much more generic container, and was
> > designed from the beginning to allow a number of slicing and
> > dimensionality tricks (see the documentation on numpy striding). You
> > can search through the mailing list from a few years ago to find a
> > discussion about three dimensional sparse matrices, and the conclusion
> > was the same: SciPy supports 2-d (in the sense of two real dimensions)
> > sparse matrices only.
> Thanks for your answer!
> I think a matrix with shape (10,0) would be as "2-d" as a (10,1) shaped
> matrix. Both have two dimensions, but neither one has both axes longer
> than 1. I don't mean to consider 0-d, 1-d, 3-d or N-d matrices, but
> empty 2-d matrices. I just don't see why there is this limitation for
> sparse matrices that zero is not a valid length for an axis.

In principle, sparse matrices should behave as much like dense matrices as
possible.  Since numpy ndarrays and matrices allow a dimension to have
length 0, it is a reasonable expectation for sparse matrices to allow this
also.  Could you file a ticket for this? Click on the "bug reports" link
here: http://projects.scipy.org/scipy


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