Subject: [FFC-dev] degrees of freedom in discontinuous elements

From: "Dag Lindbo" <[email-masked]>
Date: Mon, 23 Oct 2006 14:21:01 +0200 (MEST)

Hi all,

I'm using an appropriate mixture of continous and discontinuous elements
in my FFC/DOLFIN work (with a great deal of sucess). Now, I'd like to know
how the degrees of freedom are arranged for discontinuous elements and how
that goes into the DOLFIN Vectors.

For a 'Discontinuous Lagrange' order 0 triangular element, is it correct
that the degree(s) of freedom is just the value on the edge? I.e. a Vector
in DOLFIN for a Function on this element would contain [value at edge 0,
value at edge 1, ... ]?

For a 'Discontinuous Lagrange' order 1 triangular element, I can't really
guess what the logical ordering is. Please help.

Thanks a lot!
Dag Lindbo

---

From: "Garth N. Wells" <[email-masked]>
Date: Mon, 23 Oct 2006 14:35:09 +0200

> in DOLFIN for a Function on this element would contain [value at edge 0,

No, it's for elements, not edges. The position i in the vector
corresponds to the degree of freedom belong to element i.

> guess what the logical ordering is. Please help.

The ordering is per element. Hence, for a discontinuous linear function,
positions 0, 1 & 2 in the vector correspond to element 0, and positions
3, 4 & 5 correspond to the degrees of freedom of element 2, etc.

Garth

> Thanks a lot!
> Dag Lindbo
> 
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