On Sun, Oct 18, 2009 at 01:15:46PM -0400, mspieg wrote:
>
> On Oct 16, 2009, at 6:04 PM, Anders Logg wrote:
>
>
> 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?
>
>
> Thanks Anders,
> I haven't been using iterators because I've been overloading eval(double*
> values, Data& data) and getting the cells passed through data during assembly
>
> the issue is that I'm not necessarily evaluating at the position and cell in
> data, but at another point and cell derived from the current location and cell
> (it's basically a particle tracking problem).
>
> Ideally, given data I would set another Data structure (data_prime) with the
> new point, cell and ufc_cell, then call eval as needed. As long as the cost
> to
> construct a cell is small, it will probably be easy enough to do with the
> current code (the problem is I need to do this at every quadrature point, and
> I
> found previously that construction of UFCCell at every point was exceptionally
> expensive).
>
> Anyway, I'll play around a bit more and if I have specific issues or design
> questions, I'll let you know.
>
> cheers
> marc
ok. Sounds good. Let us know if you discover (by profiling or similar)
that the cost is large for creating a Cell. If so we may consider some
fixes for it.
--
Anders
>
>
>
>
>
>
> 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.
>
>
>
>
> 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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>
> ----------------------------------------------------
> 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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