[firedrake] High-contrast Stokes problem

[Lawrence Mitchell]

Hi Loic,

> On 6 Feb 2017, at 12:58, Loic Gouarin <loic.gouarin at math.u-psud.fr> wrote:
> 
> Thanks Lawrence for your answer.
> 
> I works perfectly and we can't do more simple !!!
> 
> I have a last question. I don't want to use a Q2-Q1 elements for the Stokes problem but a 4Q1-Q1 elements which means that linear elements for velocity live on a mesh that is once more refined globally than the elements for pressure.


Right now we don't support these kind of "isoQ1" elements.  I think it would be good to do so (since, amongst other things, they're good for preconditioning high order elliptic problems).  The problem you encounter is that right now there's no support for building problems like this where some of the function spaces come from different meshes.

We have intentions to support this, but it's quite a lot of work to get right.

Cheers,

Lawrence