Re: FYI: sparse indexed assignment rewritten

[David Bateman]

Jaroslav Hajek wrote:
> On Wed, Apr 14, 2010 at 3:44 PM, John W. Eaton <address@hidden> wrote:
>   
> > On 13-Apr-2010, Jaroslav Hajek wrote
> >     
> > | 3. simple grep query shows that the interpreter uses nzmax at
> > | suspiciously many places. I bet some of those usages are wrong and
> > | should be nnz, but it requires individual approach. So get ready for
> > | mysterious crashes, just in case.
> >
> > I guess we need to look at all nzmax uses and decide whether they
> > should be nnz instead.  Are there any simple rules for when nzmax is
> > required?
> >     
>
> nzmax is now (as it should have always been) just the amount of space
> allocated for nz elements. So probably anything that merely reads the
> matrix wants to use nnz(). An exception is conversion (conversions
> should preserve nzmax because of spalloc), but I think I already
> handled that.
>
>   
I started to look at this and have a question. For the octave file 
formats do we want to save the sparse matrix in a way that preserves the 
values of nzmax if it is different than nnz? If we do, then we need to 
change the format as only one of these values is currently saved. A 
similar issue exists for the matlab file format.. They save the value of 
nzmax in the tag and nnz can be derived from the element length (given 
in bytes). However as I no longer have access to matlab I'm unsure if 
matlab uses this to save the value of nzmax or not.. What does

s = spalloc (10,10,10);
save -v6 f.mat s
clear all
load f.mat
nzmax(s)

give in a recent version of matlab?

Cheers
David