Are you using std::cout to print a message out?
libMesh (by default) eats all std::cout output on all processors other than
processor zero. You can use the command-line option of "--keep-cout" to
keep that from happening... or you can print to std::err (which is
normally what I do in these cases).
Derek
On Fri, Aug 28, 2015 at 12:50 PM Andrew Donaldson Davis <davi...@mit.edu>
wrote:
> Hello all,
>
> You might have to forgive me if this is a silly question but I'm having
> some trouble understanding how LibMesh initializes MPI.
>
> I have the code:
>
> using namespace std;
> namespace mpi = boost::mpi;
>
> int main(int argc, char **argv) {
> mpi::environment env(argc, argv);
>
> unique_ptr<mpi::communicator> worldComm =
> unique_ptr<mpi::communicator>(new mpi::communicator);
>
> auto libmeshInit = make_shared<libMesh::LibMeshInit>(argc, argv,
> MPI_Comm(*worldComm));
>
> cout << " size: " << worldComm->size() << " rank: " << worldComm->rank()
> << endl;
>
> return 0;
> }
>
> which I expect to have an output like:
>
> size: 4 rank: 0
> size: 4 rank: 1
> size: 4 rank: 2
> size: 4 rank: 3
>
> However, I am instead seeing the output:
>
> size: 4 rank: 0
>
> If I comment out the line auto libmeshInit =
> make_shared<libMesh::LibMeshInit>(argc, argv, MPI_Comm(*worldComm)); (i.e.,
> I do not initalize LibMesh) then I get the output I expected.
>
> Is this behavior expected? or what I am doing wrong?
>
> The problem I am running into is that the mesh is distributed over all four
> processes but when I loop over the elements:
>
> // first element
> libMesh::MeshBase::const_element_iterator el =
> mesh.active_local_elements_begin();
>
> // last element
> const libMesh::MeshBase::const_element_iterator elEnd =
> mesh.active_local_elements_end();
>
> // loop through the elements
> for( ; el!=elEnd; ++el ) { /* DO SOME STUFF */ }
>
> I only "touch" the elements on the rank 0 process.
>
> Thanks for your help,
> Andy
>
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