how to get all the singular values of the matrix?

[Matthew Knepley]

On Jan 14, 2008 11:24 AM, Yujie <recrusader at gmail.com> wrote:
> Dear Matt and Hong:
>
> Based what you said, it looks like a little difficult to evalute the matrix
> in PETSc, especailly regarding a big dimension. However, when I select
> iterative methods, how to select a suitable one based on some evaluation?
> Could you give me some advice? thanks a lot.

If I knew how to choose a method, I would retire. Anyone who tells you that they
can is outright lying. The only alternative is to try them all. That
is why we built
PETSc.

  Matt

> Regards,
> Yujie
>
> On 1/14/08, Hong Zhang <hzhang at mcs.anl.gov> wrote:
> >
> > If you want few selected eigen solutions of sparse matrix,
> > you should use sparse eigen solver. Take a look at'
> > slepc (http://www.grycap.upv.es/slepc/)
> > or use slepc interface with arpack.
> >
> > Hong
> >
> >
> > On Mon, 14 Jan 2008, Yujie wrote:
> >
> > > Thank you for your advice.
> > > I have used -ksp_compute_eigenvalues_explicitly to get the eigen values.
> > > However, it is very very
> > > slow because the dimension of the matrix is about ten thousand.
> > >
> > > Yujie
> > >
> > > On 1/14/08, Matthew Knepley <knepley at gmail.com> wrote:
> > >>
> > >> You can use
> > >>
> > >>
> > >>
> http://www-unix.mcs.anl.gov/petsc/petsc-as/snapshots/petsc-current/docs/manualpages/KSP/KSPComputeEigenvaluesExplicitly.html
> > >>
> > >> with and without a preconditioner. We have not coded the SVD
> > >> counterpart, but you can use
> > >>
> > >>
> > >>
> http://www-unix.mcs.anl.gov/petsc/petsc-as/snapshots/petsc-current/docs/manualpages/KSP/KSPComputeExplicitOperator.html
> > >>
> > >> and then call the LAPACK yourself.
> > >>
> > >>   Matt
> > >>
> > >> On Jan 13, 2008 11:23 PM, Yujie <recrusader at gmail.com> wrote:
> > >>> Hi, everyone
> > >>>
> > >>> I want to select iterative methods by observing the singular values
> > >>> decompostion of the matrix. However, I don't know how to get all the
> > >>> singular values of the matrix in PETSc. I know the command
> > >>> "-ksp_monitor_singular_value" may get the max and min singular values
> at
> > >>> each iteration. How to get the singular values of the matrix I want to
> > >>> solve? In addition, when I use the preconditioned iterative method,
> how
> > >> to
> > >>> get the singular values of the preconditioned iterative operator?
> > >>>
> > >>> thanks a lot.
> > >>>
> > >>> Regards,
> > >>> Yujie
> > >>>
> > >>
> > >>
> > >>
> > >> --
> > >> What most experimenters take for granted before they begin their
> > >> experiments is infinitely more interesting than any results to which
> > >> their experiments lead.
> > >> -- Norbert Wiener
> > >>
> > >>
> > >
> >
> >
>
>



-- 
What most experimenters take for granted before they begin their
experiments is infinitely more interesting than any results to which
their experiments lead.
-- Norbert Wiener