package be.ac.vub.ir.mpi;

import mpi.MPI;

class MPIBarrierWithReduction {
	final static int NUMBEROFRUNS = 10;
	
	static float average(int[] data) {
		float sum = 0;
		for (int element : data) {
			sum += element;
		}
		return sum / data.length;
	}
	
	public static void main(String[] args) {
		int[] allData;
		int[] theSum;
		int[] privateData = new int[1];
		
		MPI.Init(args);
		int PROCESSCOUNT = MPI.COMM_WORLD.Size();
		int rank = MPI.COMM_WORLD.Rank();
		
		if (rank == 0) {
			theSum = new int[1];
			allData = new int[PROCESSCOUNT];
		}
		else {
			theSum = new int[1];
			allData = null;
		}
		
		MPI.COMM_WORLD.Scatter(allData, rank, 1, MPI.INT, privateData, 0, 1, MPI.INT, 0);
		for (int i = 0; i < NUMBEROFRUNS; ++i) {
			privateData[0] = i * rank;
			/*
			 //Using Gather
			MPI.COMM_WORLD.Gather(privateData, 0, 1, MPI.INT, allData, rank, 1, MPI.INT, 0);
			if (rank == 0) {
				System.out.println("Average at run " + i + ":" + average(allData));
			}
			*/
			// using Reduce
			MPI.COMM_WORLD.Reduce(privateData, 0, theSum, 0, 1, MPI.INT, MPI.SUM, 0);
			if (rank == 0) {
				float avg = (float) ((float)theSum[0] / PROCESSCOUNT);
				System.out.println("Average at run " + i + ":" + avg);
			}
		}
		
		MPI.Finalize();
	}
}