[firedrake] Mapping nodal values from parent to extruded mesh

Tuomas Karna tuomas.karna at gmail.com
Wed Jun 3 19:37:22 BST 2015 

Hi,

With respect to getting correct fs.bt_masks for extruded DG elements, I 
have a FIAT branch that supports facet_support_dofs for tensor elements. 
Currently only triangular prisms work but it's straightforward to 
generalize. There were a couple of steps I wasn't sure how to best 
implement. Should I push the branch to bitbucket.org/mapdes/fiat so 
someone could take a look? This also requires a small patch in Firedrake 
functionspace.py.

- Tuomas

On 04/11/2015 12:46 AM, Miklos Homolya wrote:
> Hi Tuomas,
>
> Yes, that's correct.
> And, of course, then the callers of get_facet_element 
> (FacetQuadratureRule in particular) need to be updated to provide the 
> facet number.
>
> Miklos
>
>> On 11 Apr 2015, at 01:20, Tuomas Karna <tuomas.karna at gmail.com 
>> <mailto:tuomas.karna at gmail.com>> wrote:
>>
>> Hi Miklos,
>>
>> I see. So, if I read this correctly, the reference element 
>> two_product_cell needs get_facet_element and get_facet_transform 
>> methods? But the former needs to be generalized as the facet element 
>> depends on the facet?
>>
>> - Tuomas
>>
>> On 04/10/2015 04:04 AM, Miklos Homolya wrote:
>>> 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>
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>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>     -- 
>>>>>>     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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