> I now have one more question. In assemble_face_term function of step-33, the
> normal numerical flux is calculated. This function is called for every
> cell-neighbor pair from the assemble_system function. This means, if I am not
> wrong, at every interior face quadrature point, the numerical flux is
> calculated twice. This might be very costly. Is there a way to avoid this?
> One can probably force only one cell to calculate numerical flux at a face
> based on the face normal's orientation. But then how can we communicate the
> calculated flux to the other cell. Or even better, is it possible to loop
> over faces? We could then add contributions to both the cells sharing this
> face without double computation.
step-33 does compute interior face integrals twice.
One way I handle this is to attach a cell user index
// set cell number
unsigned int index=0;
for (typename Triangulation<dim,spacedim>::active_cell_iterator
cell=triangulation.begin_active();
cell!=triangulation.end(); ++cell, ++index)
cell->set_user_index (index);
and calculate face integral only once
for (unsigned int f=0; f<GeometryInfo<dim>::faces_per_cell; ++f)
{
if(cell->face(f)->at_boundary)
{
// boundary flux integral
}
else if(cell->neighbor_is_coarser(f))
{
// assemble from finer side
}
else if(cell->user_index() < cell->neighbor(f)->user_index())
{
// compute face integral
}
// add residual to left cell
// subtract residual from right cell
}
You add/subtract face integral to both cells adjacent to the face.
If you have adapted grid, then you assemble from the finer side.
Best
praveen
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