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. Uwe
