Re: bsxfun and sparse matrices in Matlab

[Philip Nienhuis]

Jordi Gutiérrez Hermoso wrote:
> On 3 October 2011 10:15, PhilipNienhuis<address@hidden>  wrote:
> > Jordi Gutiérrez Hermoso-2 wrote:
> > > While testing more things about auto BSX, I noticed that I missed to
> > > overload the operators for sparse matrices, and while investigating
> > > *that*, it seems like bsxfun destroys sparsity. While this may make
> > > sense for some operators (e.g. power operators), I wanted to confirm
> > > if this is what Matlab does.
> > >
> > > Can someone please confirm if the following does not produce sparse
> > > matrices?
> > >
> > >      x = sprand(1,3,1/3); y = x';
> > >      bsxfun(@plus, x, y)
> > >      bsxfun(@minus, x, y)
> > >      bsxfun(@times, x, y)
> > >      bsxfun(@rdivide, x, y)
> > >      bsxfun(@ldivide, x, y)
> > >      bsxfun(@power, x, y)
> >
> > At work (ML r2009a):
> >
> > > > x = sprand(1,3,1/3); y = x'
> > y =
> >    (3,1)       0.1270
> > > > issparse (bsxfun(@plus, x, y)
> > ans =
> >      1
> > > > issparse (bsxfun(@minus, x, y))
> > ans =
> >      1
> > > > issparse (bsxfun(@times, x, y))
> > ans =
> >      1
> > > > issparse (bsxfun(@rdivide, x, y))
> > ans =
> >      1
> > > > issparse (bsxfun(@ldivide, x, y))
> > ans =
> >      1
> > > > issparse (bsxfun(@power, x, y))
> > ans =
> >      1
> >
> > (empty lines removed)
>
> I see. Thanks. Can you please also check what the nnz for the results
> are? I see here in the Octave source a comment about how Matlab

Sorry Jordi for taking your request too literally :-)

Anyway hopefully someone else will beat me - I checked this for you in 
some lost 5 minutes before I had to rush to the train station to get 
home and tomorrow (Tue) I'm afraid I won't have much spare time :-)

P.