dolfin team mailing list archive

[Dag Lindbo <dag@xxxxxxxxxx>]

Anders Logg wrote:
> On Thu, Feb 14, 2008 at 12:00:38PM +0100, Dag Lindbo wrote:
> > > Then I suggest first finding out which cells those points lie in, then
> > > then for each cell with a point get the expansion coefficients within
> > > that cell, then multiply those coefficients with the values of the
> > > basis functions at the points.
> > >
> > > The basis functions are available from the ufc::finite_element.
> > The searching part has been sorted out. How do I get the 
> > ufc::finite_element from the function and/or the form? E.g.
> >
> > Function f(mesh, 0.0);
> > StokesTHBilinearForm a;
> > StokesTHLinearForm L(f);
> > LinearPDE pde(a, L, mesh, bcs);
> >
> > pde.set("PDE linear solver", "direct");
> > pde.solve(u, p);
> >
> > ufc::form frm = a.form(); // form() is virtual
> > ufc::finite_element fe = frm.create_finite_element();
>
> You should be able to do this:
>
>   // Create element (the '0' means create it for the space used for the
>   // first argument in the form, '1' for second etc)
>   ufc::finite_element* element = a.form().create_finite_element(0);

Thanks! In my case element->space_dimension() return 15 (dofs) which 
makes sense, since I have a Taylor-Hood element (but will problably 
switch later). However, I only want to pick out the velocity components. 
How should a mixed element be handled?

I have(u is a Function):

  Cell cell(mesh,cell_nr);
  UFCCell ufc_cell(cell);

  ufc::finite_element* fe = a->form().create_finite_element(0);
  ufc::dof_map* ufc_dof_map = a->form().create_dof_map(0);

  DofMap* dof_map = new DofMap(*ufc_dof_map, mesh);

  unsigned int* dofs = new unsigned int[dof_map->local_dimension()];
  real* basis_values = new real[fe->space_dimension()];
  real* dof_values = new real[fe->space_dimension()];

  Vector vec = u.vector();

  dof_map->tabulate_dofs(dofs,ufc_cell);
  vec.get(dof_values, dof_map->local_dimension(), dofs);

>   // Use it for a while
>   element->tabulate_basis(...);
>   ...
>
>   // Then delete it
>   delete element;