pi_great_version.cc

CFD First time code using gnuplot C++ and STL

#include <math.h> 
#include "mpi.h" 
 
int main(int argc, char *argv[]) 
{ 
    int n, rank, size, i; 
    double PI25DT = 3.141592653589793238462643; 
    double mypi, pi, h, sum, x; 
 
    MPI::Init(argc, argv); 
    size = MPI::COMM_WORLD.Get_size(); 
    rank = MPI::COMM_WORLD.Get_rank(); 
 
    while (1) { 
	if (rank == 0) { 
	    cout << "Enter the number of intervals: (0 quits)" 
		 << endl; 
	    cin >> n; 
	} 
 
	MPI::COMM_WORLD.Bcast(&n, 1, MPI::INT, 0); 
	if (n==0) 
	    break; 
	else { 
	    h = 1.0 / (double) n; 
	    sum = 0.0; 
	    for (i = rank + 1; i <= n; i += size) { 
		x = h * ((double)i - 0.5); 
		sum += (4.0 / (1.0 + x*x)); 
	    } 
	    mypi = h * sum; 
 
	    MPI::COMM_WORLD.Reduce(&mypi, &pi, 1, MPI::DOUBLE, 
				   MPI::SUM, 0); 
	    if (rank == 0) 
		cout << "pi is approximately " << pi 
		     << ", Error is " << fabs(pi - PI25DT) 
		     << endl; 
	} 
    } 
    MPI::Finalize(); 
    return 0; 
}