/*
********************************************************************

                   Example 3 ( linear_topology.c ) 

  Objective           : To find sum of 'n' integers on 'p' processors using 
                        Point-to-Point communication library calls and linear 
                        array topology. 
                        This example demonstrates the use of 
                        MPI_Init
                        MPI_Comm_rank
                        MPI_Comm_size
                        MPI_Send
                        MPI_Recv
                        MPI_Finalize

  Input               : Automatic input generation
                        The rank of each process is input on each process.

  Output              : Process with Rank 0 should print the sum of 'n' values 

  Necessary Condition : Number of Processes should be less than 
                        or equal to 8.

*********************************************************************
*/



#include <stdio.h>
#include "mpi.h"

int main(int argc,char *argv[])
{
    int	MyRank, Numprocs;
    int	value, sum = 0;
    int	Source, Source_tag;
    int	Destination, Destination_tag;
    int Root = 0;
    MPI_Status status;


    MPI_Init(&argc,&argv);
    MPI_Comm_size(MPI_COMM_WORLD,&Numprocs);
    MPI_Comm_rank(MPI_COMM_WORLD,&MyRank);
   
    if (MyRank == Root) {
	Destination     = MyRank + 1;
	Destination_tag = 0;
	MPI_Send(&MyRank, 1, MPI_INT, Destination, Destination_tag, 
		  MPI_COMM_WORLD);
    }
    else{     
       if(MyRank<Numprocs-1){
	  Source     = MyRank-1;
	  Source_tag = 0;

	  MPI_Recv(&value, 1, MPI_INT, Source, Source_tag, 
		    MPI_COMM_WORLD, &status);
	  sum = MyRank + value;
	  Destination     = MyRank+1;
	  Destination_tag = 0;
	  MPI_Send(&sum, 1, MPI_INT, Destination, Destination_tag, 
		    MPI_COMM_WORLD);

       }
       else{
          Source     = MyRank-1;
	  Source_tag = 0;

	  MPI_Recv(&value, 1, MPI_INT, Source, Source_tag, 
		    MPI_COMM_WORLD, &status);

	  sum = MyRank + value;
	  printf("MyRank %d Final SUM %d\n", MyRank, sum);
      }
    }

    MPI_Finalize();

}