dolfin team mailing list archive

[Johan Hake <johan.hake@xxxxxxxxx>]

On Thursday September 16 2010 14:13:01 Kristian Ølgaard wrote:
> On 16 September 2010 22:45, Johan Hake <johan.hake@xxxxxxxxx> wrote:
> > On Thursday September 16 2010 13:33:03 Anders Logg wrote:
> >> On Thu, Sep 16, 2010 at 01:27:07PM -0700, Johan Hake wrote:
> >> > On Thursday September 16 2010 13:15:51 Anders Logg wrote:
> >> > > On Thu, Sep 16, 2010 at 01:10:55PM -0700, Johan Hake wrote:
> >> > > > On Thursday September 16 2010 13:03:44 Anders Logg wrote:
> >> > > > > On Thu, Sep 16, 2010 at 12:51:28PM -0700, Johan Hake wrote:
> >> > > > > > On Thursday September 16 2010 12:27:57 Anders Logg wrote:
> >> > > > > > > On Thu, Sep 16, 2010 at 12:23:48PM -0700, Johan Hake wrote:
> >> > > > > > > > On Thursday September 16 2010 11:46:02 Anders Logg wrote:
> >> > > > > > > > > On Thu, Sep 16, 2010 at 11:24:34AM -0700, Johan Hake 
wrote:
> >> > > > > > > > > > Hello!
> >> > > > > > > > > > 
> >> > > > > > > > > > I added the method area to the Face class. I guess a
> >> > > > > > > > > > Face is always a triangle so it should be safe.
> >> > > > > > > > > 
> >> > > > > > > > > Yes.
> >> > > > > > > > 
> >> > > > > > > > ok
> >> > > > > > > > 
> >> > > > > > > > > > There might be other methods that can be usefull like
> >> > > > > > > > > > normal? Others?
> >> > > > > > > > > 
> >> > > > > > > > > Probably but can't think of any more right now.
> >> > > > > > > > > 
> >> > > > > > > > > > Should we do the same for Facet, but then check for
> >> > > > > > > > > > topological dimension before making the computation, a
> >> > > > > > > > > > la the generalized volume in CellTypes?
> >> > > > > > > > > 
> >> > > > > > > > > Facet should have normal but not area.
> >> > > > > > > > 
> >> > > > > > > > I wont add these now. I first thought they were straight
> >> > > > > > > > forward, but all kindoff R^1, R^2, R^3 stuff needs to be
> >> > > > > > > > checked for. Leave it for now...
> >> > > > > > > > 
> >> > > > > > > > Added a blueprint!
> >> > > > > > > 
> >> > > > > > > I thought I already did that. We have Cell.normal() which
> >> > > > > > > should handle that.
> >> > > > > > 
> >> > > > > > That just calls normal of TriangleCell or TetrahedronCell.
> >> > > > > > TriangleCell only returns a normal for topological dimension
> >> > > > > > 2.
> >> > > > > 
> >> > > > > Isn't that enough? What else do you need?
> >> > > > 
> >> > > > For a Face I need to check if it is in R^2 or R^3.
> >> > > > 
> >> > > > > > It is really not difficult, it just took some more time than I
> >> > > > > > anticipated, and I do not need the feature. I just needed area
> >> > > > > > :)
> >> > > > > 
> >> > > > > Oh so you didn't need anything else. ;-)
> >> > > > 
> >> > > > Nope! Not for the moment.
> >> > > > 
> >> > > > But now it is at least straight forward to iterate over faces of a
> >> > > > 3D mesh and calculate the area of a certain boundary domain given
> >> > > > by a MeshFunction :)
> >> > > 
> >> > > Perhaps we could have
> >> > > 
> >> > >   double::Mesh::area(const FacetFunction& boundary_markers, uint
> >> > >   boundary)
> >> > > 
> >> > > const;
> >> > 
> >> > +
> >> > 
> >> > Why not add a volume method while at it? Maybe we should let these be
> >> > free functions as it does not always make sense to get an area or
> >> > volume of a mesh?
> >> 
> >> I don't know what the dimension-independent terms are but most people
> >> would probably accept "area" as meaning the length of the boundary of
> >> a 2D domain.
> > 
> > If I had a 2D mesh and it had a method area, I would definetly think that
> > it would return the area of that mesh. But that might be just me...
> 
> Anders is talking about the area of Face/Facet of a 2D mesh which is
> where this discussion originated from.

I think he here talks aout the area of a mesh. Asking for the area of a 
subdomain of that mesh would give me a length. I think that is strange, but I 
might get used to it ;)

I think the area of a facet is different. Because it has codimension of -1 and 
follows the topology of the mesh. I realise that this argumentation can be 
used for a mesh too. But it would be strange to for example calculate the 
volume of a 2D mesh, when you actually mean the area.

The area of a face is always _the_ area as it always has a topology of 2.

Johan


> Kristian
> 
> > Johan
> > 
> >> --
> >> Anders
> > 
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