/* file: scatter2.c
   compile: cc scatter2.c -lmpi
   run: mpirun -np 4 ./a.out
*/

#include "mpi.h"
#define N 64
main( argc, argv ) 
int argc; 
char **argv; 
{ 
    int myrank; 

    int a[N], local_a[N];
    int sum, local_sum;
    int i;
    int p;
    MPI_Status status;

    MPI_Init( &argc, &argv ); 
    MPI_Comm_rank( MPI_COMM_WORLD, &myrank ); 
    MPI_Comm_size( MPI_COMM_WORLD, &p ); 

    if (myrank == 0){
      for (i=0; i<N; i++){
	a[i]=(i+1);
      }
    }
    MPI_Scatter(a, N/p, MPI_INT, local_a , N/p, MPI_INT, 0, MPI_COMM_WORLD);

    local_sum = 0;
    for (i=0; i<(N/p); i++){
      local_sum = local_sum + local_a[i];
    }

    if (myrank == 0){
      sum = local_sum;
      for (i=1; i<p; i++){
	MPI_Recv(&local_sum, 1, MPI_INT, i, 99, MPI_COMM_WORLD, &status);
	sum = sum + local_sum;
      }
    }
    else{
      MPI_Send(&local_sum, 1, MPI_INT, 0, 99, MPI_COMM_WORLD);
    }

    if (myrank == 0){
      printf("sum of each local_sum = %d\n", sum);
    }
      
    MPI_Finalize(); 
  }