Re: [Libmesh-users] Question about unique_ids

[John P. <jwp...@gm...>]

On Wed, Jan 10, 2018 at 12:38 PM, David Knezevic <dav...@ak...
> wrote:

> I'd like to use unique_ids to identify elements and nodes without worrying
> about renumbering, but before I do that I'd like to understand a bit more
> about how unique_ids are defined.
>
> In particular, what is the idea behind how we generate the unique_ids? From
> the code in replicated_mesh.C, for example, it looks like the unique_ids
> are set in add_node and add_elem, with _next_unique_id being incremented
> each time a new ID is set. This looks simple enough, but I was wondering if
> there's anything else to it?
>

That's pretty much all there is to it, at least as far as I know.


One concrete question I have is if I create two Mesh objects by reading in
> the same mesh exodus file twice, will those two meshes have matching
> unique_ids? I guess they will simply because "add_node" and "add_elem" will
> be called in the same order during those two read operations.
>

Yes, the unique ids are only unique per mesh, as the _next_unique_id is
owned by MeshBase.

I can't see why two meshes created in exactly the same way wouldn't have
the exact same unique ids for all nodes and elems.

-- 
John