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


int main() {
  int rank;
  double prefixSums[3];
  double values[3] = {1, 2, 3};

  MPI_Init(NULL, NULL);
  MPI_Comm_rank(MPI_COMM_WORLD, &rank);

  if (rank % 2 == 0)
    MPI_Scan(values, prefixSums, 3, MPI_DOUBLE, MPI_SUM, MPI_COMM_WORLD);
  else
    MPI_Exscan(values, prefixSums, 3, MPI_DOUBLE, MPI_SUM, MPI_COMM_WORLD);    
  printf("I'm rank %d, my results are %f, %f, %f\n", rank, prefixSums[0], prefixSums[1], prefixSums[2]);
  assert(prefixSums[0] == rank+1 && prefixSums[1] == 2 * (rank + 1)
	 && prefixSums[2] == 3 * (rank + 1));
  MPI_Finalize();
  return 0;
}