dolfin team mailing list archive

[Johan Hake <johan.hake@xxxxxxxxx>]

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.

Johan

> --
> Anders
> 
> > I would do this in a separate script once for each mesh, and then save it
> > to file so you do not have to do this each time you read in a mesh.
> > 
> > 
> > 
> > Johan
> > 
> > > > Johan
> > > 
> > > Best regards
> > > Neilen
> > > 
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