[petsc-users] Return value of PCFactorGetMatrix

[Matthew Knepley]

On Tue, Dec 13, 2011 at 10:48 AM, Uwe Schlifkowitz <
uwe.schlifkowitz at uibk.ac.at> wrote:

> On 13.12.2011, at 16:43, Matthew Knepley wrote:
> > On Tue, Dec 13, 2011 at 9:36 AM, Uwe Schlifkowitz <
> > uwe.schlifkowitz at uibk.ac.at> wrote:
> >
> >> On 12.12.2011, at 20:05, Barry Smith wrote:
> >> problem as described here:
> >> http://lists.mcs.anl.gov/pipermail/petsc-users/2011-August/009571.html
> >> possible, so Clemens (and I) resort to MATSOLVERPETSC to obtain D.
> >> if you really need it, but what are you using it for? Do you want the
> >> inertia? We could give that for PETSc factored matrices.
> >>
> >> K is an element stiffness matrix. K is related to displacement d and
> force
> >> f by K d = f. Since K is not invertible, a solution can be found by
> means
> >> of LDL^T decomposition where K = LDL^T .
> >>
> >> Here L is the lower triangular matrix and D is the diagonal matrix,
> which
> >> is what I am looking for. The number of negative values in D correspond
> to
> >> the number of negative eigenvalues of K and serve as an indicator of the
> >> occurrence of branching points.
> >>
> >> I am not sure if this has to do with inertia, but I am fairly new to all
> >> of this so suggestions are very welcome.
> >
> >
> > Yes, it looks like what you want
> >
> >  http://en.wikipedia.org/wiki/Sylvester's_law_of_inertia
> >
> >    Matt
> >
>
> I found MatGetInertia in petsc's documentation and i am not sure how to
> use it. I found an old example from petsc-2.3.1 (
> http://www.mcs.anl.gov/petsc/petsc-2.3.1/src/ksp/ksp/examples/tutorials/ex10.c.html), but things seem to have changed since that version. Can you give an
> example?
>

It works exactly as in this example.

  Matt


> >
> >>
> >> Uwe
>
>
>
>


-- 
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
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20111213/13705abd/attachment.htm>