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>
