[MOAB-dev] ghost/halo elements

[Ryan O'Kuinghttons]

Hi Vijay,

I've had some time to play with this now, and I have another question. 
Thank you for sending along the example code, it has been extremely 
helpful.

The example shows the ghost exchange happening between shared owned 
entities. In my experiments I've been unable to make the ghost exchange 
work, and I think that might be because my entities are not shared. The 
situation I have is entities that are owned wholly on a single 
processor, which need to be communicated to other processors which 
require them as part of a halo region for mesh based computation. In 
this situation would I need to "share" my entities across the whole 
processor space, before requesting a ghost exchange? I'm not even really 
sure what shared entities mean, is there a good place to look in the 
documentation to learn more about the terminology? Thanks,

Ryan

On 10/8/18 12:17, Vijay S. Mahadevan wrote:
> Ryan,
>
> You need to use the ParallelComm object in MOAB to call
> exchange_ghost_cells [1] with appropriate levels of ghost layers for
> your mesh. This needs to be done after the mesh is loaded, or you can
> pass this information also as part of the options when loading a file
> and MOAB will internally load the file with ghosted layers. Here's an
> example [2].
>
> Vijay
>
> [1] http://ftp.mcs.anl.gov/pub/fathom/moab-docs-develop/classmoab_1_1ParallelComm.html#a55dfa308f56fd368319bfb4244428878
> [2] http://ftp.mcs.anl.gov/pub/fathom/moab-docs-develop/HelloParMOAB_8cpp-example.html
> On Mon, Oct 8, 2018 at 1:23 PM Ryan O'Kuinghttons
> <ryan.okuinghttons at noaa.gov> wrote:
>> Hi, I am wondering if there is a way to create ghost elements in MOAB.
>> By this I mean a list of copies of elements surrounding a specific MOAB
>> element, ghost elements may exist on a different processor than the
>> source element. I see a ghost_elems class in the appData namespace, but
>> there is not much documentation on how to use it.. Thank you,
>>
>> --
>> Ryan O'Kuinghttons
>> Cherokee Nation Management and Consulting
>> NESII/NOAA/Earth System Research Laboratory
>> ryan.okuinghttons at noaa.gov
>> https://www.esrl.noaa.gov/gsd/nesii/
>>