/*
     "Hello World" MPI Test Program
    */
    #include <mpi.h>
    #include <stdio.h>
    #include <string.h>
    
    #define BUFSIZE 128
    #define TAG 0
    
    int main(int argc, char *argv[])
    {
      char idstr[32];
      char buff[BUFSIZE];
      int numprocs;
      int myid;
      int i;
      MPI_Status stat;
      /* MPI programs start with MPI_Init; all 'N' processes exist thereafter */
      MPI_Init(&argc,&argv);
      /* find out how big the SPMD world is */
      MPI_Comm_size(MPI_COMM_WORLD,&numprocs);
      /* and this processes' rank is */
      MPI_Comm_rank(MPI_COMM_WORLD,&myid);
    
      /* At this point, all programs are running equivalently, the rank
         distinguishes the roles of the programs in the SPMD model, with
         rank 0 often used specially... */
      if(myid == 0)
      {
        printf("%d: We have %d processors\n", myid, numprocs);
        for(i=1;i<numprocs;i++)
        {
          sprintf(buff, "Hello %d! ", i);
          MPI_Send(buff, BUFSIZE, MPI_CHAR, i, TAG, MPI_COMM_WORLD);
        }
        for(i=1;i<numprocs;i++)
        {
          MPI_Recv(buff, BUFSIZE, MPI_CHAR, i, TAG, MPI_COMM_WORLD, &stat);
          printf("%d: %s\n", myid, buff);
        }
      }
      else
      {
        /* receive from rank 0: */
        MPI_Recv(buff, BUFSIZE, MPI_CHAR, 0, TAG, MPI_COMM_WORLD, &stat);
        sprintf(idstr, "Processor %d ", myid);
        strncat(buff, idstr, BUFSIZE-1);
        strncat(buff, "reporting for duty\n", BUFSIZE-1);
        /* send to rank 0: */
        MPI_Send(buff, BUFSIZE, MPI_CHAR, 0, TAG, MPI_COMM_WORLD);
      }
    
      /* MPI programs end with MPI Finalize; this is a weak synchronization point */
      MPI_Finalize();
      return 0;
    }