dolfin team mailing list archive

[Anders Logg <logg@xxxxxxxxx>]

On Thu, Dec 11, 2008 at 08:08:46PM +0100, Johan Hake wrote:
> On Thursday 11 December 2008 19:28:23 Bartosz Sawicki wrote:
> > Hi,
> >
> > I'm new in Swing and python bindings, so maybe answer to my question
> > will be trivial. Could you please tell me, if it is possible to access
> > into mesh entities from python. For example:
> >
> > c = Cell(mesh, 111)
> > print c.numEntities(0)
> > ent = c.entities()
> > print ent
> >
> > gives output:
> >
> > 4
> > <Swig Object of type 'dolfin::uint *' at 0x3a26fb8>
> >
> > According to the documentation I expect that entities method "Return
> > array of indices ". 'dolfin::uint *' is propably pointer to array, but
> > ent[0] fails with "'int' object is unsubscriptable" error.
> > So how can I get elements for this array?
> 
> Hello Bartek!
> 
> Not all of the DOLFIN interface is mapped correctly to PyDOLFIN. For example 
> are there, as you correctly observed, some issues with pointers to C-arrays.
> 
> To access what vertices are included in a particular cell you can look at
> 
>   cells = mesh.cells()
> 
> For a tetrahedral mesh, this will return a numpy.array with 
> 
>   shape = (mesh.numCells(),4)
> 
> What I would like to map to the PyDOLFIN interface includes the topological 
> connection information. This would be feasable but has not yet been done.
> 
> Johan

Correct.

Until this has been fixed, one needs to work with the iterators which
are mapped correctly to Python. So you may for example to

  for cell in cells(mesh):
      for vertex in vertices(cell):
          for edge in edges(vertex):
              print edge.index()

etc.

-- 
Anders

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