ffc team mailing list archive

[Shawn Walker <walker@xxxxxxxxxxxxxxx>]

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
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