[firedrake] Mapping nodal values from parent to extruded mesh

[Miklos Homolya]

Hi,

facet_support_dofs is the same infrastructure we use to support 
geometric boundary conditions.

I have implemented geometric boundary conditions for (unstructured) 
quadrilaterals, it wasn't too complicated:
https://bitbucket.org/mapdes/fiat/pull-request/29/geometric-bcs-for-quadrilaterals/diff

For general tensor product elements it would be a bit more complicated, 
as horizontal and vertical facets are in general different. For example, 
a prism has quadrilaterals as vertical facets, but triangles as 
horizontal facets.

Regards,
Miklos


On 10/04/15 11:23, David Ham wrote:
> 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 
> <mailto: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
>>>     <mailto: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 <mailto: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 list
>>>     firedrake at imperial.ac.uk  <mailto: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
>
>
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