dolfin team mailing list archive

[Anders Logg <logg@xxxxxxxxx>]

On Mon, Mar 14, 2011 at 10:31:21AM -0700, Johan Hake wrote:
> On Monday March 14 2011 10:25:10 Anders Logg wrote:
> > On Mon, Mar 14, 2011 at 09:06:00AM -0700, Johan Hake wrote:
> > > On Monday March 14 2011 08:44:19 Neilen Marais wrote:
> > > > Johan,
> > > >
> > > > On Mon, Mar 14, 2011 at 5:21 PM, Johan Hake <johan.hake@xxxxxxxxx>
> wrote:
> > > > > On Monday March 14 2011 04:36:29 Neilen Marais wrote:
> > > > > If you have an already tetrahedralized structure, typically given by
> > > > > a coordinate array and an array of conductivities between cells and
> > > > > vertices, you can use MeshEditor. That is what MeshEditor really is
> > > > > for.
> > > > >
> > > > >
> > > > > I think the advice of not using MeshEditor is when you use it to
> > > > > construct the vertices and connectivities by hand.
> > > >
> > > > I guess I'm just worrying about performance in python, since I would
> > > > have to do one method call for each vertex and one for each tet. I may
> > > > be prematurely optimising here, but IIRC even method calls to SWIG
> > > > wrapped C++ classes have a fair amount of overhead. Since I already
> > > > have the vertex coordinates and cell -> vertex connectivity data in
> > > > arrays, it is obviously much faster to just stuff them directly into
> > > > the dolfin structures?
> > >
> > > Sure you are right that it might come with some overhead. Not sure it
> > > will be significant though, as this would probably be a one time thing?
> > >
> > > But after reading your post one more time I realize what you asked for
> > > :P, and the answer is yes! You can perfectly do what you did.
> > > mesh.cells() and mesh.coordinates() each return a NumPy array view of
> > > the actuall data. Your syntax works because NumPy allows it.
> >
> > It works because it happens to work. It's not intended usage and it
> > might break if we change the implementation MeshEditor, even if the
> > interface stays the same.
> >
> > It would be better to add some utility function for creating a Mesh
> > based on arrays.
>
> I agree.
>
> But as long as we store the coordinates and cells as contiguous arrays in the
> mesh, they will be exposed to Python through NumPy and this will just work.

Not necessarily. The MeshEditor might postpone initializing the arrays
until it has received all calls to add_cell etc and only then allocate
the arrays. So the mixing of MeshEditor.open, close and array access
only works if it is compatible with what MeshEditor does internally.

--
Anders