// collective.cc
//
// Sample program for collective communication

#include <cstdlib>
#include <fstream>
#include <vector>
#include "mpi.h"

using namespace std;

int main(void) {

  const int count=8;
  vector<int> rand_nums(count), max(count), min(count), sum(count),
    all_rand_nums;

  MPI::Init();  // initialize MPI

  int rank=MPI::COMM_WORLD.Get_rank();  // ascertain own rank
  int size=MPI::COMM_WORLD.Get_size();  // and number of processes

  srand(7*rank);  // initialize random number generator
  for (int i=0; i<count; ++i)  // throw dice
    rand_nums[i]=rand()%1000;

  if (rank==0)  // allocate space at receiving process
    all_rand_nums.resize(count*size);
  // Collect data
  MPI::COMM_WORLD.Gather(&rand_nums[0], count, MPI::INT,
                         &all_rand_nums[0], count, MPI::INT, 0); 

  // Calculate maximum, minimum, and sum and send to rank 0
  MPI::COMM_WORLD.Reduce(&rand_nums[0], &max[0], count, MPI::INT, MPI::MAX, 0);
  MPI::COMM_WORLD.Reduce(&rand_nums[0], &min[0], count, MPI::INT, MPI::MIN, 0); 
  MPI::COMM_WORLD.Reduce(&rand_nums[0], &sum[0], count, MPI::INT, MPI::SUM, 0);

  if (rank==0) { // Save results
    ofstream out("collective.out");
    for (int i=0; i<size; ++i) {
      out << "Process " << i << " :"; 
      for (int j=0; j<count; ++j)
        out << "\t" << all_rand_nums[i*count+j];
      out << endl;
    } 
    out << endl << "Maxima :";
    for (int i=0; i<count; ++i) out << "\t" << max[i];
    out << endl << "Minima :"; 
    for (int i=0; i<count; ++i) out << "\t" << min[i];
    out << endl << "Summen :";
    for (int i=0; i<count; ++i) out << "\t" << sum[i];
    out << endl;
  }

  MPI::Finalize();   // terminate MPI

  return EXIT_SUCCESS;
}