/* test of Gather communication in MPI */ 

#include "mpi.h" 
#include <iostream.h> 
#include <string.h> 

int main(int argc, char **argv) 
{ 
   int buff[100]; 
   int recvbuff[2];
   int numprocs; 
   int myid; 
   int i, k; 
   int mysum;

   MPI_Status stat; 

   MPI_Init(&argc,&argv); 
   MPI_Comm_size(MPI_COMM_WORLD,&numprocs); 
   MPI_Comm_rank(MPI_COMM_WORLD,&myid); 

   if ( myid == 0 ) 
   { 
      cout << "WE have " << numprocs << " processors" << endl;

      // -----------------------------------------------
      // Node 0 prepare 2 number for each processor
      //     [1][2]  [3][4]  [5][6] .... etc
      // -----------------------------------------------
      k = 1;
      for ( i = 0; i < 2*numprocs; i += 2 )
      {
	  buff[i] = k++;
	  buff[i+1] = k++;
      }
   }

   // ------------------------------------------
   // Node 0 scatter the array to the processors:
   // ------------------------------------------

   MPI_Scatter (buff, 2, MPI_INT, recvbuff, 2, MPI_INT, 0, MPI_COMM_WORLD);
 
   mysum = recvbuff[0] + recvbuff[1];

   MPI_Gather (&mysum, 1, MPI_INT, &buff, 1, MPI_INT, 0, MPI_COMM_WORLD);

   if ( myid == 0 )
   {
      for( i = 0; i < numprocs; i++) 
      {  
         cout << "Processor " << i << ": sum = " << buff[i] << endl;
      }
   }

   MPI_Finalize(); 
}