Re: [Libmesh-users] How to use ExodusII_IO::copy_elemental_solution in parallel?

[David K. <dav...@ak...>]

On Fri, Oct 20, 2017 at 11:38 AM, John Peterson <jwp...@gm...>
wrote:

>
>
> On Fri, Oct 20, 2017 at 9:19 AM, David Knezevic <
> dav...@ak...> wrote:
>
>> I'm using ExodusII_IO::copy_elemental_solution to copy element data to a
>> new System object, and this works fine in serial using code like the below:
>>
>> ----------------------------------------------
>>
>>   Mesh mesh(comm);
>>   ExodusII_IO exo_io(mesh);
>>
>>   if (comm.rank() == 0)
>>   {
>>     exo_io.read(path_to_mesh_file);
>>   }
>>   MeshCommunication().broadcast(mesh);
>>
>>   mesh.prepare_for_use();
>>
>>   EquationSystems es(mesh);
>>   ExplicitSystem& materials_system =
>>     es->add_system<ExplicitSystem> ("data");
>>   materials_system.add_variable ("data", CONSTANT, MONOMIAL);
>>   es->init();
>>
>>   exo_io.copy_elemental_solution(es, "data", "data");
>>
>> ----------------------------------------------
>>
>>
>> However, in parallel I hit the error "ERROR, ExodusII file must be opened
>> for reading before copying an elemental solution!" at the start of
>> copy_elemental_solution.
>>
>> As far as I know (e.g. based on namebased_io.C) we should only call
>> "read" on proc 0, so I don't see how to make this work in parallel, since
>> in that case exo_io is only "opened for reading" on proc 0.
>>
>> Does anyone have any suggestions on this? (John, I gather that you were
>> the author of most of the ExodusII reader stuff, so I thought you might
>> know the answer?)
>>
>
> Hmm... I think copy_elemental_solution() is only designed to work in
> serial, so could we just guard the parts the parts of that function that
> read from the file in "if (rank==0)"?
>
> In addition, we would only error out if the file is not open for reading
> on proc 0...
>

OK, that makes sense. I think we could just wrap the whole method (up to
solution->close) in "if (rank==0)", and remove the "if" around
system.solution->set so that all values are set on proc 0 and then
communicated when we close the vector. Do you agree?

David