#include <stdio.h>

#include <stdlib.h>

#include <ctype.h>

#include <malloc.h>

#include <mpi.h>

#define buffsize 1024*1024 

void main(int argc, char **argv )

{

int myid,numprocs;

int i;

int mbytes = 1;

int indmax;

double t1, t2;

char *buffer;

MPI_Status status; 

MPI_Init(&argc, &argv);

MPI_Barrier(MPI_COMM_WORLD); 

MPI_Comm_size(MPI_COMM_WORLD, &numprocs);

MPI_Comm_rank(MPI_COMM_WORLD, &myid); 

MPI_Barrier(MPI_COMM_WORLD);  

buffer = malloc(buffsize*mbytes);

if (!buffer) { printf(" Slave %d failed to malloc %d mbytes\n", myid, mbytes); }

indmax = buffsize*mbytes;

MPI_Barrier(MPI_COMM_WORLD);  

if (myid == 0) 

{

  for (i = 0; i < indmax; i++) { buffer[i] = myid; }

  t1 = MPI_Wtime();

  MPI_Send(buffer, indmax, MPI_CHAR, 1, 1, MPI_COMM_WORLD);

  MPI_Recv(buffer, indmax, MPI_CHAR, numprocs - 1, 1, MPI_COMM_WORLD, &status);

  t2 = MPI_Wtime();

  printf("Round Trip time for %d megabytes to %d nodes is %.3lf seconds\n", mbytes, numprocs, t2-t1);

  for (i = 0; i < numprocs; i++) 

   printf("Slave %d signed %d\n", i, buffer[i]);

}

else  

{

  MPI_Recv(buffer, indmax, MPI_CHAR, myid - 1, 1, MPI_COMM_WORLD, &status); 

  buffer[myid] = toascii(myid);

  MPI_Send(buffer, indmax, MPI_CHAR, ((myid + 1) % numprocs), 1, MPI_COMM_WORLD);

} 

MPI_Barrier(MPI_COMM_WORLD); 

MPI_Finalize();

fflush(stdout);

}