1. I tried out the p4est_ghost_expand as Wolfgang suggested, but it gives me
an error because for some reason I get
if(cell->is_ghost){cell->user_flag_set()==true} after the calls
communicate_dof_indices_on_marked_cells() in dof_handler_policy.cc line 3875.
I believe the function communicate_dof_indices_on_marked_cells() in line 3492
in the same file exchanges the dof indices (sending the local cells that are
ghost somewhere else and receiving its ghost cells from other procs) but the
unpack function should identify all the cells marked as ghost and receive the
corresponding indices from the pack function, right ? Or have I misunderstood
something here ?
Hm, good point. When we decide who each process needs to send the locally
owned DoF indices to (so that they can be set on ghost cells on the receiving
process), we determine the cells in question by asking whether one of their
vertices is adjacent to a ghost cell -- in other words, whether a cell is at
the boundary of the locally owned subdomain.
But if you have more than one layer of ghost cells, then this is not enough. I
think you need to extend the logic in a way where each process sends a list of
its ghost cells to the owning process of these cells, and then gets the
information back for exactly those cells. That may be a little bit of work,
but I don't think it's going to be terribly difficult to implement. Let us
know if you need help with this.
2. All places in example 40 (my reference) for the matrix and rhs assembly,
you use the locally_relevant_dofs and locally_owned_dofs. As you say in the
Glossary
<http://dealii.org/developer/doxygen/deal.II/DEALGlossary.html#GlossParallelScaling>,
for locally_active_dofs
" Since degrees of freedom are owned by only one processor, degrees of freedom
on interfaces between cells owned by different processors may be owned by one
or the other, so not all degrees of freedom on a locally owned cell are also
locally owned degrees of freedom."
And hence you assemble your local matrices with the locally_owned_dofs. But
for the overlapped decomposition, I need to assemble matrices including the
"ghost cells" . In my case, they wouldn't be ghost cells but locally owned
cells but duplicated between logically overlapping processes. I am not really
sure how to go about doing this.
This is what I tried to explain in my previous email: on each process, you
need a separate enumeration of all degrees of freedom that live on that
process (either on locally owned or ghost cells). This enumeration must be
independent of the "global" enumeration we typically use in deal.II which
uniquely splits up all DoF indices among the processors.
Best
W.
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Wolfgang Bangerth email: [email protected]
www: http://www.math.colostate.edu/~bangerth/
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