Re: [Libmesh-users] problems with mesh output: possible solution

[Michael P. <mpo...@pu...>]

Hello John,

I played with it, and this is what worked for me.

#include <vector>
#include <sstream>
using namespace std;

#define private public//to get access to 
libMesh::LibMeshInit._vtk_mpi_controller

#include "libmesh/mesh_generation.h"
#include "libmesh/mesh.h"
#include "libmesh/vtk_io.h"
#include "libmesh/libmesh.h"
#include "vtkMPIController.h"
int main(int argc, char ** argv)
{

   MPI_Init(&argc, &argv);

   {
     libMesh::LibMeshInit init (argc, argv,MPI_COMM_WORLD);
     int rank;
     MPI_Comm_rank(MPI_COMM_WORLD, &rank);

     vtkMPICommunicator* mcomm = 
vtkMPICommunicator::GetWorldCommunicator()->NewInstance ();
     mcomm->SplitInitialize (mcomm, rank, 0);

     init._vtk_mpi_controller->SetCommunicator (mcomm);

     libMesh::Mesh mesh(libMesh::Parallel::Communicator(MPI_COMM_SELF));
     libMesh::MeshTools::Generation::build_cube (mesh,
                                                 10, 10, 5, 0.0, 2.0, 
0.0, 3.0, 0.0, 4.0,libMesh::HEX8);


     if (rank == 0)
     {
       libMesh::VTKIO out(mesh);
       out.write("mesh1.pvtu");
     }
   }
   MPI_Finalize();
   return 0;



}


What do you think? Can you provide an access to 
libMesh::LibMeshInit._vtk_mpi_controller?
Or there is a better solution?
Michael.

On 06/13/2018 12:28 PM, John Peterson wrote:
>
>
> On Wed, Jun 13, 2018 at 10:14 AM, Michael Povolotskyi 
> <mpo...@pu... <mailto:mpo...@pu...>> wrote:
>
>     Thank you John,
>
>     I do have some MPI code before LibMeshInit in my real application.
>
>     Also, If I do not call MPI_Finalize at the very end I'm getting
>     warning messages from MPI.
>
>     Thank you for you explanation with .pvtu, I have changed my code
>     to  libMesh::VTKIO out(mesh); out.write("mesh1.pvtu");   and this
>     worked.
>
>     Do you have any suggestions for  the Problem #2 that I reported?
>
>     It seems to me that the problem is that the communicator of the
>     Mesh object is smaller than the communicator of the VTK. This
>     causes a problem for me.
>
>
> Hmm, I don't think we have considered this use case in the past, the 
> vtkMPIController is initialized in libmesh.C, and it must be assuming 
> MPI_COMM_WORLD...
>
>   _vtk_mpi_controller = vtkMPIController::New();
>   _vtk_mpi_controller->Initialize(&argc, const_cast<char ***>(&argv), 
> /*initialized_externally=*/1);
> _vtk_mpi_controller->SetGlobalController(_vtk_mpi_controller);
>
> In order for the parallel VTK writer to work, the Mesh probably 
> therefore also needs to be using MPI_COMM_WORLD.
>
> -- 
> John