Mixed finite element discretization with petsc?

[Jed Brown]

On Thu, Oct 8, 2009 at 14:20, Thomas Witkowski
<thomas.witkowski at tu-dresden.de> wrote:
>> This representation is purely symbolic.  There is a permutation of the
>> dofs that would look like this, but it's not the ordering that you
>> actually want to use
>>
>
> okay, but with a different ordering I'll lose symmetry of the system.

No, it is a symmetric permutation.


For indefinite problems, I implement the preconditioning matrix using
MatShell where I provide MatGetSubMatrix (which either returns the
cached submatrix or assembles it on demand, the former is sometimes
more efficient and more convenient for profiling).  You should have a
reasonable idea about how to precondition the subsystems before you go
this route.


Jed