dolfin team mailing list archive

[Shawn Walker <walker@xxxxxxxxxxxxxxx>]

I understand what you are saying, but the ordering of the vertices is such 
that the first three vertices (0,1,2) are exactly the same as they were 
before.  This would be done no matter what order polynomial map you used. 
So, it seems to me it should be fine.

However, to be sure, I can modify the ufc stuff such that the coordinates 
variable only reads in the first three vertices.  So this would be 
EXACTLY as it was before.  I would then create a new ufc::cell variable 
called `map_coordinates' (if you have a better name, please suggest) and 
this would read in the 6 vertices.  And in Tabulate_Tensor, if higher 
order is desired, then the `map_coordinates' will be used to compute the 
FEM matrix.

This seems safe, though a little redundant.  Of course, one must be 
careful when creating the higher order mesh .xml file and ensure that the 
first three vertices correspond to the usual triangle vertices.

I also want to make sure that the extra `map_coordinates' is available to 
be modified with a loop in dolfin.  This would be necessary for an ALE 
method when the mesh is deforming.

- Shawn

On Wed, 20 Aug 2008, Anders Logg wrote:

> On Wed, Aug 20, 2008 at 07:15:06PM +0100, Garth N. Wells wrote:
> > Anders Logg wrote:
> > > I'm not sure this will work. If you attach 6 vertices to a triangle by
> > >
> > >   <triangle index="0" affine="false" v0="0" v1="1" v2="2" v3="4" v4="5" v5="6"/>
> > >
> > > then all sorts of things will break (I imagine). A triangle always has
> > > three vertices.
> >
> > I noticed this too. It would make some things troublesome.
> >
> > > The geometry of the triangles is separate.
> > >
> > > Maybe we could just add extra data which could be "control points" for
> > > the cell facets? For P2 it would be the edge/face midpoints.
> >
> > I like the idea of defining facet data which would contain the necessary
> > info.
>
> A problem with defining facet data is that the facet numbering is not
> known a priori. It depends on the algorithm used by DOLFIN to compute
> the facets from the cells. So we can't store for example a mesh
> function over the facets since the facet numbering may change.
>
> When we read input from VMTK, we need to read facet data (boundary
> markers) and these are stored relative to the cell to which the facet
> belongs and the local number of the facet relative to the cell (which
> is unique).
>
> There is an example in data/meshes/aneurysm.xml.gz.
>
> --
> Anders