Subject: [FFC-dev] nodemap -> dofmap

From: "Garth N. Wells" <[email-masked]>
Date: Mon, 04 Dec 2006 17:22:22 +0100

Could "node" be changed to to "dof" in FFC output? To me, a node 
represents a position on an element at which one or more dofs live.

Garth

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From: Anders Logg <[email-masked]>
Date: Mon, 4 Dec 2006 17:47:21 +0100

I think of a node as a member of the dual basis for P in the
definition of a finite element in Brenner-Scott. A node in FFC is
always associated with an entity, like the second node of entity 0 of
an entity of dimension 1 (the second node on the first edge).

So I would very much like to keep the name "node".

See also

    http://www.fenics.org/hg/ufc?f=1e97408cde10;file=src/ufc/ufc.h

where we have

    tabulate_nodes()
    evaluate_node()

But we could discuss what to call it. Other opinions?

/Anders

On Mon, Dec 04, 2006 at 05:22:22PM +0100, Garth N. Wells wrote:
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> FFC-dev mailing list
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From: "Garth N. Wells" <[email-masked]>
Date: Mon, 04 Dec 2006 18:03:41 +0100

> So I would very much like to keep the name "node".

OK, but this does clash with accepted terminology. In both Brenner & 
Scott and Ciarlet, nodes are defined as points.

>     http://www.fenics.org/hg/ufc?f=1e97408cde10;file=src/ufc/ufc.h

This is partly why I made the suggestions. I saw this terminology in 
some code from Martin. "nodes" gives the impression of points.

Garth

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From: Anders Logg <[email-masked]>
Date: Mon, 4 Dec 2006 18:12:51 +0100

> Scott and Ciarlet, nodes are defined as points.

Yes, when I look again, they do use "node" for a point, but also refer
to "nodal variables" as the name of the linear functional you evaluate
to get the "nodal value".

> some code from Martin. "nodes" gives the impression of points.

ok. More opinions?

/Anders

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From: "Garth N. Wells" <[email-masked]>
Date: Mon, 04 Dec 2006 19:20:22 +0100

> to get the "nodal value".

Sure, this is normal FE terminology -  nodal variables for the degrees 
of freedom at a node. Also, "nodal value" in general case should be 
"nodal values" :).

Garth

-- 

Dr. Garth N. Wells
Faculty of Civil Engineering and Geosciences
Delft University of Technology
Stevinweg 1
2628 CN Delft
Netherlands

tel.   +31 15 278 7922
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e-mail [email-masked]
url    http://www.mechanics.citg.tudelft.nl/~garth

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From: Anders Logg <[email-masked]>
Date: Mon, 4 Dec 2006 19:23:09 +0100

> of freedom at a node. Also, "nodal value" in general case should be 

ok, but how do you say this when the nodal variable is an integral
over an edge?

Can you still say "at a node"? Or is "node" not used then?

/Anders

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From: "Garth N. Wells" <[email-masked]>
Date: Mon, 04 Dec 2006 19:32:34 +0100

> Can you still say "at a node"? Or is "node" not used then?

I wouldn't use node, I would use "degree of freedom". Are you thinking 
of a Nedelec element?

Garth

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From: Anders Logg <[email-masked]>
Date: Mon, 4 Dec 2006 19:40:30 +0100

> I wouldn't use node, I would use "degree of freedom". Are you thinking 

I was thinking BDM.

So your suggestion is to never use "node" and always use "dof"?

/Anders

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From: "Garth N. Wells" <[email-masked]>
Date: Mon, 04 Dec 2006 19:51:51 +0100

> So your suggestion is to never use "node" and always use "dof"?

Not quite. I would restrict the meaning of "node" to a position point, 
and use degree of freedom for a value that can change, typically 
representing the amplitude of some function.

I looked quickly in a few  books and they refer to "degrees of freedom" 
for BDM and Nedelec elements.

Garth

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From: Anders Logg <[email-masked]>
Date: Mon, 4 Dec 2006 20:31:19 +0100

> for BDM and Nedelec elements.

I asked Ridg to settle this. Here's a quote:

  There is a good reason to differentiate between the point at which
  a nodal variable acts and the nodal variable (the linear functional).
  Using DOF for this concept is probably the best idea, since the
  terminology "nodal variable" still refers to a "node" and does not
  sound quite right for an edge integral.

                                  Ridg

So I give up, let's call it "dof"/"DOF"! :-)

/Anders

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From: "Garth N. Wells" <[email-masked]>
Date: Mon, 04 Dec 2006 20:34:56 +0100

> So I give up, let's call it "dof"/"DOF"! :-)

At least you made me work hard :).

Garth