ffc team mailing list archive

[Anders Logg <logg@xxxxxxxxx>]

On Thu, Jul 08, 2010 at 01:02:43PM +0100, Garth N. Wells wrote:
>
>
> On 08/07/10 12:59, Anders Logg wrote:
> >On Thu, Jul 08, 2010 at 12:00:38PM +0100, Garth N. Wells wrote:
> >>
> >>
> >>On 08/07/10 11:49, Kristian Oelgaard wrote:
> >>>On 8 July 2010 08:22, Garth N. Wells<gnw20@xxxxxxxxx>   wrote:
> >>>>On Jul 8 2010, Anders Logg wrote:
> >>>>
> >>>>>On Wed, Jul 07, 2010 at 10:34:39PM +0100, Kristian Oelgaard wrote:
> >>>>>>
> >>>>>>On 7 July 2010 20:22, Garth N. Wells<gnw20@xxxxxxxxx>   wrote:
> >>>>>>>
> >>>>>>>
> >>>>>>>On 07/07/10 20:14, Anders Logg wrote:
> >>>>>>>>
> >>>>>>>>On Wed, Jul 07, 2010 at 06:26:20PM +0100, Kristian Oelgaard wrote:
> >>>>>>>>>
> >>>>>>>>>Supporting CellVolume makes it possible to do:
> >>>>>>>>>
> >>>>>>>>>CG = FiniteElement("Lagrange", triangle, 2)
> >>>>>>>>>DG = FiniteElement("DG", triangle, 0)
> >>>>>>>>>v = TestFunction(DG)
> >>>>>>>>>f = Coefficient(CG)
> >>>>>>>>>vol = triangle.v
> >>>>>>>>
> >>>>>>>>Would it be better to call it vol or volume instead of v? Or does it
> >>>>>>>>have to be a one-letter word?
> >>>>>>>>
> >>>>>>>
> >>>>>>>. . . or call it 'volume'.
> >>>>>>
> >>>>>>It can be whatever we want, I just followed what was already there.
> >>>>>>Should we then rename 'd', 'n' and 'x' to 'geometric_dimension',
> >>>>>>'facet_normal', and 'spatial_coordinate' while we're at it?
> >>>>>
> >>>>>I think d, n, x are fine, but v does not necessarily look like a
> >>>>>volume to me (it looks like a test function).
> >>>>>
> >>>>
> >>>>I agree - d, n and x are all commonly used, but v for volume isn't.
> >>>
> >>>I changed 'v' to 'volume' and fixed a few bugs along the way.
> >>>
> >>>On a related note, should we implement CellDiagonal too?
> >>>We use cell.diagonal() for MeshSize in SpecialFunctions.h of DOLFIN
> >>>and since we often use MeshSize for the 'h' coefficient in DG forms
> >>>e.g., PoissonDG we could remove the need for this function evaluation.
> >>>The code to compute the CellDiagonal could just be copied from
> >>>IntervalCell, TriangleCell and TetrahedronCell of DOLFIN and dumped in
> >>>codesnippets.py.
> >>>
> >>
> >>What if we call it 'Circumradius'?
> >>
> >>I recall that the agreed not have have CellSize because of the
> >>ambiguity in its definition, but circumradius is unambiguous, so I
> >>vote to add it.
> >
> >Isn't 'diameter' better? It is shorter and well-defined
> >(2*circumradius).
> >
>
> 'diameter' isn't well defined. We can use it, but we would need to
> define it as being 2*circumradius.
>
> Garth

Why isn't it well-defined? The diameter of a set T is

  d = sup_{x,y \in T} ||x - y||

and that should be the same as 2*circumradius unless I'm mistaken.

--
Anders

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