/*====================================================================*/
   /* MPI Method
   /*====================================================================*/
   
   /*--------------------------------------------------------------------*/
   /* Node A posts nonblocking receive */
   int size;
   char *buf;
   MPI_Request req;
   MPI_Status status;
   
   buf = (char *)malloc(size);
   MPI_Irecv( buf, size, MPI_BYTE, MPI_ANY_SOURCE, id, MPI_COMM_WORLD, &req );
   
   (do some computing)
   
   MPI_Wait(&req, &status);
   free(buf);
   
   /*--------------------------------------------------------------------*/
   /* Node B does a nonblocking send */
   int size;
   char *buf;
   MPI_Request req;
   MPI_Status status;
   
   buf = (char *)malloc(size);
   MPI_Isend( buf, size, MPI_BYTE, destnode, id, MPI_COMM_WORLD, &req );
   
   (do some computing)
   
   MPI_Wait(&req, &status);
   free(buf);
   
   /*--------------------------------------------------------------------*/
   /* Barrier */
   
     MPI_Barrier( MPI_COMM_WORLD );
   
   
   /*--------------------------------------------------------------------*/
   /* Global sum */
   
     float fpt, work;
     MPI_Allreduce( &fpt, &work, 1, MPI_FLOAT, MPI_SUM, MPI_COMM_WORLD);
   
   /*--------------------------------------------------------------------*/
   /* Broadcast */
     char buf[size];
   
     MPI_broadcast(buf, size);