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: > > > > On Dec 12, 2011, at 11:49 AM, Uwe Schlifkowitz wrote: > > > >> I'm continuing Clemens Domanig's work. Currently I'm stuck at his > problem as described here: > http://lists.mcs.anl.gov/pipermail/petsc-users/2011-August/009571.html > >> > >> As far as I understand, getting the diagonal matrix from MUMPS is not > possible, so Clemens (and I) resort to MATSOLVERPETSC to obtain D. > > > > We could add support for MatGetDiagonal() for PETSc factored matrices > 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. > > > > > > Barry > > > > 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 > > 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/20111213/113acf64/attachment.htm>
