// passOne.c
// Run this with 2 processes (0 and 1).  This program passes the value of PI from processor 1 to 
//  processor 0.
// Note that MPI_Send and MPI_Recv use the address (&) of the variable sent or passed.
// MPI_Recv uses the address of the status variable as its last argument.

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

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

	count = 1;
	if (rank == 0) {
		MPI_Recv(&pi, 1, MPI_DOUBLE, 1, 10, MPI_COMM_WORLD, &status);
		printf("Data received from process 1:\n");
		printf("%.20f\n", pi);
	}
	else {
		if (rank == 1) {
			pi = M_PI;
			MPI_Send(&pi, count, MPI_DOUBLE, 0, 10, MPI_COMM_WORLD);
		}
	}
    
    MPI_Finalize();
    return 0;
}

/*

CRAY SV1:

cc passOneMPI.c  

mpirun -np 2 a.out
Data received from process 1:
3.14159265358979000000

*/