[firedrake] RectangleMesh

[David Ham]

Dear Floriane,

The thing to understand is that there is no guaranteed relationship between
vertex number and the location of that vertex. Vertex numbers are (as far
as the user is concerned), completely arbitrary. This is fine because none
of the correct ways to access vertices  depend on what the order is.

When you say that you are applying a change of coordinates, what do you
mean? Do you mean that you are changing the coordinate values before you
compute? If so, please tell us mathematically what you are attempting to do
and we can tell you the right way to do it.

Regards,

David

On Thu, 23 Feb 2017 at 14:08 Floriane Gidel [RPG] <mmfg at leeds.ac.uk> wrote:

> Dear all,
>
>
> I have a question concerning the mesh definition with RectangleMesh:
>
>
> I define my  mesh as a Rectangle mesh, with quadrilaterals as:
>
> hor_mesh = RectangleMesh(Nx, Ny, 10.0, 1.0, quadrilateral=True).
>
>
> As my functions are only (x,t) dependent, I'd like to get only one element
> in y, i.e. Ny=1.
>
> However I noticed that if I set Ny=1, then the x-coordinates are swapped
> from 10.0 to 0.0 . Basically, I obtain
>
> hor_mesh.coordinates.dat.data[:,0] = [10.0 10.0 9.9 9.9 ...... 0.0]
>
> instead of
>
> hor_mesh.coordinates.dat.data[:,0] = [0.0 0.0 0.1 0.1 ........ 10.0] (that
> I obtain for Ny>1)
>
>
> Can someone explain me what happens there ? Is there a way to avoid that ?
>
> And if I use the integral on ds(1), will it be at x=0 of x=10 in that case?
>
>
> The reason why I want to understand this is because I apply a change of
> coordinate in some part of the domain (let's say for x<L<Lx) and the
> coordinate transform does not give the right result for Ny=1 (while it does
> for Ny>1).
>
>
> Thanks in advance for your help,
>
> Floriane
>
>
>
> --
Dr David Ham
Department of Mathematics
Imperial College London
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