[petsc-users] Return value of PCFactorGetMatrix

[Uwe Schlifkowitz]

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