On Tue, 13 Oct 2009, Joa Ljungvall wrote:

> #5  0x00007fff81116bfc in __cxa_throw ()
> #6  0x000000010512afa4 in RemoteElem::n_nodes ()
> #7  0x000000010510acf4 in DofMap::dof_indices ()
> #8  0x000000010510e2d9 in DofMap::add_neighbors_to_send_list ()
>
> This I don't understand at all...

Hmm... there was a bug last year that looked like this, but it was
fixed before 0.6.3 was released.

It may be that you've inadvertently triggered the same problem that
the bug did, though:

When we refine an element, we need to create any new nodes its
children will have, or we need to point them to the appropriate
existing node in the mesh.  We look for that existing node by
location: calculate the point where we'd build a new node, see if any
node exists at that point yet, if so attach to it and if not then
build a new one.

But what happens if you refine one element, create a hanging node,
then *move the hanging node*?  When you refine the element's neighbor,
it will look to see if a node exists yet on that edge or face, the
answer will be "no", and a new node will be created.  This tears the
topology of the mesh, which is a nasty bug that can manifest as the
incorrect creation of a RemoteElem in our find_neighbors() algorithm.
(but which should have triggered a libmesh_assert() earlier - did you
run in devel or dbg mode?)

Anyway, the solution is probably to, after you've looped over all
nodes, loop over all constraint equations in the dof map and apply
them to nodes' xyz coordinates.
---
Roy

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