I iterate a collection of cells, and for each one I have to iterate the
active descendants.
Given a coarse cell, I use a FilteredIterator
<https://www.dealii.org/current/doxygen/deal.II/classFilteredIterator.html>
to iterate active descendants, but the method *set_to_next_positive*
significantly slows down the code. Something I'd expect runs in 0.1 s takes
10 s. The filter is:
*<start C++ code>*
class ActiveChild
{
public:
// Use CellId
<https://www.dealii.org/current/doxygen/deal.II/classCellId.html> to check
if is ancestor.
CellId parent;
ActiveChild(const CellId &parent)
: parent(parent) {}
template <typename Iterator>
bool operator()(const Iterator &cell) const
{
// cell is the potential descendant.
return parent.is_ancestor_of(cell->id());
}
};
*<end C++ code>*
I iterate active descendants like:
*<start C++ code>*
using ChildIt = FilteredIterator<typename DoFHandler<2,
3>::active_cell_iterator>;
Triangulation<2, 3> tria;
unsigned int level; // level of coarse cell.
unsigned int coarse_cell_index;
CellAccessor<2, 3> coarse_cell(&tria, level, coarse_cell_index);
ChildIt cell(ActiveChild(coarse_cell.id()));
ChildIt endc(ActiveChild(coarse_cell.id()), dof_handler.end());
*// This method, set_to_next_positive, is very slow.*
*cell.set_to_next_positive(dof_handler.begin_active());*
for (; cell != endc; ++cell)
{
// I use DoFHandler accessor to get global dof indices.
cell->get_dof_indices(global_dofs);
// Do stuff ...
}
*<end C++ code>*
Is there a better alternative to iterate active descendants? Why is
*set_to_next_positive* so slow here?
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