> > Yes. Though it seems confusing to me that you call these variables
> > locally_*_cells, because they really are index sets for degrees of freedom,
> > not cells.
>
> OK, I misunderstood it. I thought the numbering of the dof is same as that of
> the cell since the degrees of freedom is 1 in FE_DGQ(0).
> They are still different, right?
They are *conceptually* different. Whether or not they are different *in
practice* is a different question, but you should never *assume* that they are
the same.
> > Yes, this does not work. That's because you confuse the index of the cell
> and
> > the index of the DoF that lives on it. You want the latter.
>
> Again now I understand they are different.
>
> However, for my project, I need to access both
>
> DoFHandler<dim> dof_handler;
> DoFHandler<dim> dof_handler_dg;
>
> at the same time.
>
> If I use the following loop,
>
> for (const auto &cell : opt->dof_handler.active_cell_iterators())
> {
> ...
> }
>
> how can I access to dof_handler_dg?
You can have two iterators into the two DoFHandlers that run in lock step just
like you do:
> My attempting solution is to set up multiple iterator, just as in the
> tutorial:
> https://www.dealii.org/current/doxygen/deal.II/group__Iterators.html,
>
> typename Triangulation<dim>::active_cell_iterator ti =
> opt->triangulation.begin_active();
> typename DoFHandler<dim>::active_cell_iterator di1 =
> opt->dof_handler.begin_active();
> typename DoFHandler<dim>::active_cell_iterator di2 =
> opt->dof_handler_dg.begin_active();
>
> Therefore, I set up the loop as follows,
>
> while (cell != opt->triangulation.end())
> {
> // do someting
>
> ++ti;
> ++di1;
> ++di2;
> }
>
> (Note: now I can access to the cell-based vector x successfully as follows,
> di2->get_dof_indices(local_dof_indices_dg);
> unsigned int local_dof_indices_dg_int = local_dof_indices_dg.at(0);
> opt->x(local_dof_indices_dg_int);
> )
>
>
> However, I found this method is very time-consuming compared to "for (const
> auto &cell : opt->dof_handler.active_cell_iterators())", like 11s vs. 1 s.
You mean time consuming to program, or to execute? The loop itself is cheap;
if it's slow, you need to figure out which part of the body is slow.
> My question now is: is there other method to access multiple DoFHandler
> or/and
> Triangulation?
You could just do everything in one DoFHandler. That's what I usually do: Put
all solution variables into the same DoFHandler.
Best
W.
--
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Wolfgang Bangerth email: [email protected]
www: http://www.math.colostate.edu/~bangerth/
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