Getting ready

The example code (hello-mpi.cpp, downloaded from http://www.mpitutorial.com), which we will compile in this recipe, will initialize the MPI library, have every process print its name, and eventually finalize the library:

#include <iostream>

#include <mpi.h>

int main(int argc, char **argv) {
  // Initialize the MPI environment. The two arguments to MPI Init are not
  // currently used by MPI implementations, but are there in case future
  // implementations might need the arguments.
  MPI_Init(NULL, NULL);

  // Get the number of processes
  int world_size;
  MPI_Comm_size(MPI_COMM_WORLD, &world_size);

  // Get the rank of the process
  int world_rank;
  MPI_Comm_rank(MPI_COMM_WORLD, &world_rank);

  // Get the name of the processor
  char processor_name[MPI_MAX_PROCESSOR_NAME];
  int name_len;
  MPI_Get_processor_name(processor_name, &name_len);

  // Print off a hello world message
  std::cout << "Hello world from processor " << processor_name << ", rank "
            << world_rank << " out of " << world_size << " processors" << std::endl;

  // Finalize the MPI environment. No more MPI calls can be made after this
  MPI_Finalize();
}