ffc team mailing list archive

[Anders Logg <logg@xxxxxxxxx>]

DOLFIN assumes that the mesh is ordered locally so that the local
vertices on each triangle are ordered increasingly. Take a look at the
XML files in data/meshes in DOLFIN and you'll see what I mean.

-- 
Anders


On Tue, Jun 23, 2009 at 12:11:13PM -0400, Shawn Walker wrote:
> ok.  But I have one more question.
> 
> Is there any kind of re-ordering of nodes that dolfin does internally?  I 
> thought I remembered seeing this.  I have been trying to compare two 
> matrices, and it looks like the entries are the same, except the ordering 
> is a little different.
> 
> - Shawn
> 
> On Tue, 23 Jun 2009, Kristian Oelgaard wrote:
> 
> > Quoting Shawn Walker <walker@xxxxxxxxxxxxxxx>:
> >
> >> Hello.  I need to know how FFC orders P2 Lagrange nodes.  I need to know
> >> this in order to compare a FEM matrix that I created in another program.
> >>
> >> For example, say you have one triangle with the following nodes:
> >>
> >> [0 1 2 3 4 5]
> >>
> >> Where is the #3 node in relation to the #0, #1, and #2 nodes?  Is #3
> >> opposite the #0 node?
> >
> > Yes.
> >
> > I usually look at the tabulate_dofs() function, for the P2 case:
> >
> > dofs[0] = c.entity_indices[0][0];
> > dofs[1] = c.entity_indices[0][1];
> > dofs[2] = c.entity_indices[0][2];
> > unsigned int offset = m.num_entities[0];
> > dofs[3] = offset + c.entity_indices[1][0];
> > dofs[4] = offset + c.entity_indices[1][1];
> > dofs[5] = offset + c.entity_indices[1][2];
> >
> > So you see that the first 3 dofs are the vertices, the next 3 are the midpoints
> > of the edges. Then you need to know the UFC ordering of edges to figure out
> > that e0 is the edge which does not contain vertex 0 (opposite to v0) etc.
> >
> > Kristian
> >
> >> - Shawn
> >> _______________________________________________
> >> FFC-dev mailing list
> >> FFC-dev@xxxxxxxxxx
> >> http://www.fenics.org/mailman/listinfo/ffc-dev
> >>
> >
> >
> >
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