[petsc-users] Stokes problem with DA and MUMPS

[Jed Brown]

On Thu, Feb 24, 2011 at 10:56, gouarin <loic.gouarin at math.u-psud.fr> wrote:

> I set block size to 3 for my matrix but I'm not sure that I can use it
> because I don't have the same number of points for each field. I don't hnow
> how petsc defines the blocks.
>
> How can I use again fieldsplit for the preconditioner ?
>

It is worth switching to petsc-dev for this:

1. Use DMComposite to "glue" the velocity and pressure DAs together.

2. Call PCSetDM (or the higher level KSPSetDM, SNESSetDM, or TSSetDM as
appropriate) and pass in the DMComposite.

Now when you -pc_type fieldsplit, it will automatically pick up the fields
from the DMComposite (in the order they were registered). That would give
you two splits in this case.

You can use DMComposite with petsc-3.1, but you have to create index sets
yourself and call PCFieldSplitSetIS().
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