/* simple MPI program to exchange values between two processes
   this illustrates the use of send and receive

   first create a hosts file, then boot LAM by means of lamboot

   then compile and execute this program by executing:
       hcc exchange.c -lmpi
       mpirun -w -c 2 a.out    */

#include <mpi.h>

main(int argc, char *argv[]) {

   int myid, otherid, size;
   int length = 1, tag = 1;
   int myvalue, othervalue;
   MPI_Status status;
 
   /* initialize MPI and get own id (rank) */
   MPI_Init(&argc, &argv);
   MPI_Comm_rank(MPI_COMM_WORLD, &myid);
   MPI_Comm_size(MPI_COMM_WORLD, &size); 
   if (size!=2) {
     printf("use exactly two processes\n");
     exit(1);
   }

   if (myid == 0) {
      otherid = 1; myvalue = 14;
   } else {
      otherid = 0; myvalue = 25;
   }
   printf("process %d sending %d to process %d\n", myid, myvalue, otherid);
   MPI_Send(&myvalue, 1, MPI_INT, otherid, tag, MPI_COMM_WORLD);
   MPI_Recv(&othervalue, 1, MPI_INT, MPI_ANY_SOURCE, MPI_ANY_TAG,
            MPI_COMM_WORLD, &status);
   printf("process %d received a %d\n", myid, othervalue);

   MPI_Finalize();
}