dolfin team mailing list archive

[Anders Logg <logg@xxxxxxxxx>]

On Thu, Apr 02, 2009 at 11:12:20AM -0400, Shawn Walker wrote:
> Hello all.
> 
> I have finally got some time to put in (at least the first stage) the 
> higher order mesh stuff for triangles
> mapped with P2 lagrange elements. Just to remind you, the agreement that 
> we came up with was this:
> 
> 1. The local mapping for each element is independent of whatever finite 
> elements you are using.  Thus, there
> should be a completely different description of the mapping.

Sounds good.

> 2. This info will be stored in MeshGeometry with extra data structures.

Sounds good.

> 3. The info to store is (i) all the higher order vertex position data, and 
> (ii) the `DoFmap' for your
> particular map.  Storing the extra vertex data is just like storing the 
> usual 3 triangle coordinates.

Are you thinking of using DofMap for this?

> 4. Eventually, for computing the local finite element matrices, there just 
> needs to be a short subroutine
> that returns the higher order vertex data (for a specific cell) to be used 
> by, say, the code generated by
> FFC.

Yes.

> My question is about the dofmap.  It is certainly reasonable to store it 
> similarly to the vertex data.  But
> there is a problem if the mesh is locally refined.  It seems like it will 
> be a pain to modify this data
> structure.  Any suggestions for this?

When a mesh is locally refined, an entirely new mesh is created. The
mesh class stores all data in large arrays so all mesh data needs to
be copied to new data structures anyway.

> Remember, we do NOT want to use a function space here.  This was already 
> discussed!

I know, but I keep forgetting why. :-)

We just removed all the precompiled elements which means one must
always instantiate the correct function spaces maunually (at least in
C++). The question here is how to create/number the extra nodes. The
form compilers already know how to generate code for this, and it
would be extra work to try to duplicate that code for the mapping of
higher order coordinates. Do you have a good plan for how to number
the coordinates?

-- 
Anders

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