how to get all the singular values of the matrix?

[Yujie]

:). Thank you for your explanation.

Yujie

On 1/14/08, Matthew Knepley <knepley at gmail.com> wrote:
>
> 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
>
>
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