[firedrake] Mapping nodal values from parent to extruded mesh

[David Ham]

Hi Tuomas,

Concerning the sets of spaces which this will work for, I think that the
current implementation probably works for any horizontal space but only for
vertical CG. One could just try relaxing the test in that case.

The reason for the restriction to vertical CG is that fs.bt_masks uses the
topological association of nodes with mesh entities in order to work out
which nodes are on the top or bottom of the cell. In order to allow DG in
the vertical, it would be necessary to support the geometric definition (ie
which basis functions do not vanish on the top/bottom).

If you look at functionspace.py:78 you can see where the bottom and top
masks are generated. This uses entity_closure_dofs() from FIAT. In order to
use the geometric definition of dofs one would need to support using
facet_support_dofs() (which is how BC maps are set up at
functionspace.py:375). Currently FIAT TensorFiniteElement objects do
support entity_closure_dofs() but nobody has done the legwork to get them
to support facet_support_dofs.

Concerning documentation, COFFEE is deplorably underdocumented (although
the author is on this list so maybe this will change ;). The actual
available AST nodes are only "documented" by reading the source:
https://github.com/coneoproject/COFFEE/blob/master/coffee/base.py However,
you are fundamentally writing a PyOP2 kernel, and the C api for that *is*
documented at: http://op2.github.io/PyOP2/kernels.html so that hopefully
helps somewhat.

Otherwise, keep asking here or in IRC (IRC tends to get faster responses,
at least between about 10am and 8pm UK time).

BTW, any chance of seeing you at FEniCS '15?

Cheers,

David



On 10 April 2015 at 02:44, Tuomas Karna <tuomas.karna at gmail.com> wrote:

>  Hi all,
>
> A couple of questions regarding those extruded mesh -> parent mesh copy
> operations,
>
> A while back I got the reverse 2d->3d copy working with a hard-coded pyop2
> kernel (like in mesh extrusion). I'm not familiar with COFFEE syntax, is
> there documentation/examples somewhere?
>
> The 3d->2d copy routine in extrusion_extraction branch checks that the
> function space is CG. Does this method easily generalize to other spaces?
> DGxCG prisms seem to work OK. I'm also interested in using DGxDG and
> RTxCG/DG spaces.
>
>
> Cheers,
>
> Tuomas
>
>
> On 03/05/2015 10:24 AM, Tuomas Karna wrote:
>
> Thanks David,
>
> This is great, I'll try doing the reverse operation.
>
> - Tuomas
>
> On 03/05/2015 08:20 AM, David Ham wrote:
>
> Hi Tuomas,
>
>  This wasn't there this morning but I've implemented one of the cases
> (pulling out the top and bottom maps). The result is in the
> extrusion_extraction branches of both PyOP2 and Firedrake. The 2d->3d
> operation would be rather similar except that you'd have to interrogate the
> fiat_element on the extruded Function in order to determine which extruded
> nodes are "on top of" the 2d nodes you have.  Unfortunately I won't have
> time to do that one soon (huge amounts to do before SIAM CSE next week) but
> feel free to have a try and complain when it doesn't work!
>
>  Cheers,
>
>  David
>
> On 4 March 2015 at 22:23, Tuomas Karna <tuomas.karna at gmail.com> wrote:
>
>> Hi all,
>>
>> I'd need to copy nodal values between fields on parent and extruded
>> meshes. For example, copy 2d->3d (constant over vertical) or 3d->2d
>> (extract surface/bottom level). The horizontal function space is the
>> same. Is there an easy way to do this? Is there a map of extruded nodes
>> somewhere?
>>
>> Thanks,
>>
>> Tuomas
>>
>>
>>
>> _______________________________________________
>> firedrake mailing list
>> firedrake at imperial.ac.uk
>> https://mailman.ic.ac.uk/mailman/listinfo/firedrake
>>
>
>
>
>  --
>  Dr David Ham
> Departments of Mathematics and Computing
> Imperial College London
>
> http://www.imperial.ac.uk/people/david.ham
>
>
> _______________________________________________
> firedrake mailing listfiredrake at imperial.ac.ukhttps://mailman.ic.ac.uk/mailman/listinfo/firedrake
>
>
>
>


-- 
Dr David Ham
Departments of Mathematics and Computing
Imperial College London

http://www.imperial.ac.uk/people/david.ham
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