[Trilinos-Users] null space removal
Christopher K. Newman
cnewman at lanl.gov
Wed Sep 8 12:55:12 MDT 2010
Hi Mike-
We have a nonlinear ocean model with many coupled pdes, which we are
trying to solve for the steady state using jfnk with gmres with a finite
difference jacobian as preconditioner. Gmres does not seem to converge
and upon examination of the finite difference jacobian with matlab a
clear checkerboard nullspace mode appears in one of the components. I
believe it is manifested in a divergence term. I am wondering if this
null space accounts for the poor convergence and if it can be remedied
by a projection orthogonal to the nullspace similar to what is done for
the pure Neumann problem with a constant nullspace.
Chris
On 9/8/10 12:31 PM, Heroux, Michael A wrote:
> Hi Chris,
>
> This is something I have wanted to add for a long time, but as far as I know it is not generally available. ML provides this capability itself, if you are using it. It would be fairly straight-forward to add this. Can you describe your specific situation?
>
> Thanks.
>
> Mike
>
>
> On 9/8/10 1:07 PM, "Newman, Christopher K. (LANL)"<cnewman at lanl.gov> wrote:
>
> Is there a way to automatically remove a known null space during an iterative solve? Dare I say, similar to KSPSetNullSpace in Petsc. Or is the preferred method user implementation of a projection operator?
>
> Thanks,
>
> Chris
>
--
Christopher K. Newman
Los Alamos National Laboratory, T-3 Email: cnewman at lanl.gov
PO Box 1663 MS B216 Phone: 505 606 0647
Los Alamos, NM 87545 Fax: 505 665 5926
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