[petsc-users] Nullspace for a coupled system of equations

Jed Brown jedbrown at mcs.anl.gov
Fri Aug 17 14:30:11 CDT 2012

On Fri, Aug 17, 2012 at 2:27 PM, Thomas Witkowski <
thomas.witkowski at tu-dresden.de> wrote:

> I want to solve the block triangular system as described above. My problem
> is, that it has a one dimensional null space, but I'm not able to define
> it. My question is: does anyone can give me an advice how to EITHER compute
> the null space explicitly OR how to solve the system in such a way that the
> null space is considered by the solver. The only constraint is that I
> cannot split the system of equations into two independent solve for both
> variables. I know that from this description its not clear why there is
> this constraint, but it would take too long to describe it.

What are the operators involved? Why can't you determine the null space
with a pencil and paper? Can you use PCFieldSplit in the solution process?
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