dolfin team mailing list archive

[Shawn Walker <walker@xxxxxxxxxxxxxxx>]

On Mon, 25 Aug 2008, Anders Logg wrote:

> Actually, this would work and would require the least amount of
> modification of current code.
>
> We can just store a vector-valued P2 Function for the coordinates (or
> any other order).
>
> The XML format already handles input/output of Functions so this would
> be easy.
>
> A couple caveats though:
>
> 1. This requires having the corresponding elements and dof maps
> precompiled in DOLFIN. This should be ok, considering they are already
> there.

Just to clarify, you mean if we were to use 5th order continuous lagrange 
elements for the mesh element geometry, we must make sure this particular 
finite element is implemented.  That is certainly reasonable!

> 2. It also makes an assumption about the numbering of degrees of
> freedom (and mesh entities) always being the same. This can be handled
> by adding a new tag <dofmap> under <function> that contains the dofs
> explicitly (not the signature of the FFC dof map).
>
> The XML format could be something like
>
>  <mesh celltype="triangle" dim="2">
>    <vertices size="2868">
>      <vertex index="0" x="0.534923" y="0.326073"/>
>      ...
>    </vertices>
>    <cells size="5400">
>      <triangle index="0" v0="76" v1="914" v2="1153"/>
>      ...
>    </cells>
>    <coordinates>
>      <function>
>
>      </function>
>    </coordinates>
>  <mesh

ok, I guess you would need to add an attribute to the `function' to 
specify what kind of finite element it is.  You could also add a boolean 
function to the <coordinates> section that would indicate whether the 
element is indeed curved or not.

> This would mean storing the vertex coordinates twice, but I think we
> can live with that. The <coordinates> section would be optional. If it
> exists, it will allocate a Function inside MeshGeometry which would
> otherwise be null.

As long as this function is easily accessible by the relevant routines 
(i.e. Tabulate_Tensor) this seems ok.  Then it would just be a matter of 
how FFC implements the computation.

Is there a specific demo that reads in a function similar to this?  I 
would like an example to look at.

- Shawn