ffc team mailing list archive

[Andy Ray Terrel <aterrel@xxxxxxxxxxxx>]

Okay thanks for the response!

-- Andy

On Thu, Jun 4, 2009 at 4:50 AM, Jed Brown <jed@xxxxxxxx> wrote:
> Andy Ray Terrel wrote:
>> Wouldn't that ignore the coupling in solving Stokes to begin with?
>>
>> You want to be able to add an integral operator perhaps something like
>> the mass matrix (m) with a constant function m(1, p). Added to the
>> problem.
>
> I suppose you could do this, but it adds a lot of nonzeros (a dense row
> and column) and it's really not necessary.  This leaves two choices:
>
> 1. "Pin" pressure at one node and "normalize" (peculiar word choice)
> the result.
>
> 2. Inform the Krylov solver that constant pressure is in the null space
> of the operator.  See KSPSetNullSpace in PETSc, Trilinos must support
> this as well.  This option is usually preferable unless you need to use
> a direct solver.
>
> Jed
>
>
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