// bcast.c
// This program using MPI_BCAST (MPI Broadcast) to "broadcast" data - in this
// case PI - from the root process (processor 0) to all the other processors.
// Note that ALL of the processors have MPI_Bcast, not just the root process.
// One of the parameters in MPI_Bcast provides the numerical value of the root
// process.  In this program the root process is 'source', and it equals 0.
// This means that 0 is the root process sending the broadcast.  If the
// process is not 0, then it is receiving the broadcast from 0 (the 'source'
// parameter in MPI_Bcast)
// Make sure you see which parameter in MPI_Bcast represents the root process.

#include <stdio.h>
#include <math.h>
#include "mpi.h"

int main(int argc, char **argv)
{
	int rank, size;
	MPI_Status status;
	double pi;
	int i, count, source;
	
	MPI_Init(&argc, &argv);
	MPI_Comm_rank(MPI_COMM_WORLD, &rank); 
	MPI_Comm_size(MPI_COMM_WORLD, &size); 

	count = 1;
	source = 0;
	if (rank == source) {
		pi = M_PI;
		printf("Rank %d is broadcasting %.10f\n", rank, pi);
	}
	
	MPI_Bcast(&pi, 1, MPI_DOUBLE, source, MPI_COMM_WORLD);
	if (rank != source) {
		printf("Rank %d receives %.10f from process %d\n", rank, pi, source);
	}
    
	MPI_Finalize();
	return 0;
}

/*

CRAY SV1:

cc bcast.c  
mpirun -np 8 a.out

Rank 0 is broadcasting 3.1415926536
Rank 1 receives 3.1415926536 from process 0
Rank 2 receives 3.1415926536 from process 0
Rank 3 receives 3.1415926536 from process 0
Rank 4 receives 3.1415926536 from process 0
Rank 5 receives 3.1415926536 from process 0
Rank 6 receives 3.1415926536 from process 0
Rank 7 receives 3.1415926536 from process 0

mpirun -np 4 a.out

Rank 0 is broadcasting 3.1415926536
Rank 2 receives 3.1415926536 from process 0
Rank 3 receives 3.1415926536 from process 0
Rank 1 receives 3.1415926536 from process 0


*/