Re: large sparse matrix

[Carlo de Falco]

On 1 Sep 2009, at 09:14, Jaroslav Hajek wrote:

> On Tue, Sep 1, 2009 at 1:12 AM, Carlo de  
> Falco<address@hidden> wrote:
> > On 31 Aug 2009, at 21:53, David Bateman wrote:
> > > Yes, but the configuration of SuiteSparse in terms of the pivot
> > > threshold is the default that TIm Davis sets for Octave and whatever
> > > mathworks chose to use for matlab. So don't expect exactly the
> > > behavior.
> > I see...
> >
> > > In Octave what does
> > >
> > > matrix_type(A)
> > > give?
> >
> >
> >  >> matrix_type (A)
> > ans = Positive Definite
> >  >>
> >
> > > If it doesn't flag your matrix as PD then there might be an issue
> > > with the detection of the matrix and PD and the solver used in
> > > Octave will be LU.
> >
> > on the other hand what surprises me is that:
> >
> >  >> issparse (B)
> > ans =  1
> >  >> matrix_type (B)
> > ans = Rectangular
> >  >> issparse (A)
> > ans =  1
> >  >> mat = [A B' spalloc(rows(A),1,0); B spalloc(rows(B),columns(A),1)
> > E'; spalloc(columns(A),1,1) E 0];
> >  >> matrix_type (mat)
> > ans = Full
> >  >> issparse (mat)
> > ans =  1
> >
> > why is mat marked as full???
>
> Full is what you get when nothing special about the matrix is
> discovered. Did you expect something else? The matrix is obviously not
> positive definite, as seen from its construction, and I can see no
> apparent other structure (triangularity or bandedness), though it of
> course depends on the values of A, B and E.
>
> hth

Well, the matrix is of course symmetric by construction,
but I don't think there's much more...
But actually the reason I was surprised that it is marked as
"Full" is that I thought this mark had to do with its storage format.
Maybe another name like, e.g., "Generic" would have been less  
misleading...
Thnaks for the info!
c.