#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <unistd.h>
#include "mpi.h"

/*
Aim:

  Print the "Hello World" message from each process spaned, including
  the process ID from the operating system and the MPI rank.

Note:

  Processes are represented by a unique "rank" (integer) and ranks are 
  numbered 0, 1, 2, ..., N-1. 

  MPI_COMM_WORLD means "all the processes in the MPI application." It 
  is called a communicator and it provides all information necessary to 
  do message passing.

*/
int main(int argc,char ** argv )
{
    // Rank of the calling process in the communicator group
    int rank;
    // Total number of processes in the communicator group
    int size;
    // Hostname
    char hostname[1024];

    // Initialize the MPI execution environment 
    MPI_Init( &argc, &argv );
    // MPI_COMM_WORLD is the default communicator setup by MPI_Init()  

    /* 
    Typically, a process in a parallel application needs to know who 
    it is (its rank) and how many other processes exist. A process 
    finds out its own rank by calling MPI_Comm_rank() and the total 
    number of processes is returned by MPI_Comm_size().
    */
    MPI_Comm_rank( MPI_COMM_WORLD, &rank );
    MPI_Comm_size( MPI_COMM_WORLD, &size );

    // Get the process ID from the OS
    pid_t pid = getpid();
    // Get the hostname
    gethostname(hostname, 1024);

    printf( "Hello world %s.%d [%d/%d]\n",hostname , pid, rank, size);

    // Terminates MPI execution environment and clean up the process
    MPI_Finalize();

    return 0;
}