[MOAB-dev] loading a VTK mesh in parallel (.pvtu)

[Lorenzo Alessio Botti]

Dear all,
I have recently written a MOAB reader/writer for .vtu and .pvtu files, that is VTK unstructured grids and parallel VTK unstructured grids in xml format. 
The only issue for the inclusion in MOAB (let me know if that would be interesting for you) is that I’m using an open-source xml reader instead of the FileTokenizer included into MOAB. 

The .pvtu parallel reader works fine, each process loads an independent .vtu file containing his portion of the grid and creates a PARALLEL_PARTITION entity set for his ParallelComm. 
Actually the number of .vtu files must be equal to the number of processes, so the reader is less flexible than with the native .h5m file format. 
Eventually the reader could be modified to handle a number of partitions different from the number of processes.

What I really would like to do next is to include in each .vtu portion of the grid the informations required to run in parallel 
(e.g. ghost cells, shared entities) so to avoid calling resolver_shared_entities(...) and exchange_ghost_cells(….) in parallel. 
Nevertheless, I would like to be able to call exchange_tags(….) and reduce_tags(….) in parallel, once the grid has been loaded.
What would I need to do so? I guess that to exchange tags across processes each shared entity must know the processors it need to communicate with. 
How can I achieve this behaviour? Which informations I need to add to the mesh files?

Any help is appreciated, thanks!
Lorenzo