dolfin team mailing list archive

[Anders Logg <logg@xxxxxxxxx>]

On Fri, Oct 16, 2009 at 03:34:06PM -0400, mspieg wrote:
> Hi All,
>   I'm trying to update a working 0.9.3 code to  0.9.4, and I need to understand
> the new interfaces for Function::eval a bit better.
>
> I had things working fine with the old interface
>
> Function::eval (double *values, const double *x, const ufc::cell &ufc_cell,
> uint cell_index)
>
> and am trying to understand how to efficiently use
>
> Function::eval (double *values, const double *x, const Cell &dolfin_cell, const
> ufc::cell &ufc_cell)
>
> (My codes need to do a large number of evals at arbitrary points and cells
> efficiently)
>
> among other things, is there an easy way to update the index of a cell, without
> constructing a new Cell every time? (or shouldn't I be worrying about this).

Constructing a cell should not cost that much. It just stores the
index, the dimension and a reference to the mesh.

If you are using iterators over a mesh, then you already have the cell
by dereferencing the pointer. The typical usage would be

UFCCell ufc_cell(mesh);
for (CellIterator cell(mesh); !mesh.end(); ++cell)
{
  ufc_cell.update(*cell);

  f.eval(values, x, *cell, ufc_cell);
}

But perhaps you don't use iterators?

> Anyway, I need to play with things a bit more, but looking at the source code
> for eval,  I was also wondering
>  if lines 320 and 321 are required as line 322 doesn't seem to require cell.
>
>  typo? bug? or general ignorance on my part (probably the latter).

Yes, lines 320-321 should be removed. Thanks for noticing. I've fixed
this now.

--
Anders


> cheers
> marc
>
> void Function::eval(double* values, const Data& data) const
>
> 00311 {
> 00312   assert(values);
> 00313   assert(_function_space);
> 00314
> 00315   // Check if UFC cell if available and cell matches
> 00316   if (data._dolfin_cell && _function_space->has_cell(*data._dolfin_cell))
> 00317   {
> 00318     // Efficient evaluation on given cell
> 00319     assert(data._ufc_cell);
> 00320     const uint cell_index = data._ufc_cell->entity_indices[data._ufc_cell->topological_dimension][0];
> 00321     Cell cell(_function_space->mesh(), cell_index);
> 00322     eval(values, data.x, *data._dolfin_cell, *data._ufc_cell);
> 00323   }
> 00324   else
> 00325   {
> 00326     // Redirect to point-based evaluation
> 00327     eval(values, data.x);
> 00328   }
> 00329 }
>
> ----------------------------------------------------
> Marc Spiegelman
> Lamont-Doherty Earth Observatory
> Dept. of Applied Physics/Applied Math
> Columbia University
> http://www.ldeo.columbia.edu/~mspieg
> tel: 845 704 2323 (SkypeIn)
> ----------------------------------------------------
>
>

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