#include <stdio.h>
#include “mpi.h”
int main ( int argc, char **argv )
{
 int numtasks, rank, next, prev, buf [2], tag1 = 1, tag2 = 2;
 MPI_Request reqs [4];
 MPI_Status stats [2];
 MPI_Init ( &argc, &argv );
 MPI_Comm_size (MPI_COMM_WORLD, &numtasks);
 MPI_Comm_rank (MPI_COMM_WORLD, &rank);
 prev = rank -1;
 next = rank + 1;
 if ( rank == 0 ) prev = numtasks -1;
 if ( rank == ( numtasks -1 ) ) next = 0;
 MPI_Irecv ( &buf [0], 1, MPI_INT, prev, tag1, MPI_COMM_WORLD, &reqs [0]
);
 MPI_Irecv ( &buf [1], 1, MPI_INT, next, tag2, MPI_COMM_WORLD, &reqs [1]
);
 MPI_Isend ( &rank, 1, MPI_INT, prev, tag2, MPI_COMM_WORLD, &reqs [2] );
 MPI_Isend ( &rank, 1, MPI_INT, next, tag1, MPI_COMM_WORLD, &reqs [3] );
 
 MPI_Waitall (4, reqs, stats );
 MPI_Finalize();
 return 0;
} 
 

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