#ifndef CA_UWATERLOO_ALUMNI_DWHARDER_CENTRAL_LIMIT_THEOREM
#define CA_UWATERLOO_ALUMNI_DWHARDER_CENTRAL_LIMIT_THEOREM

#include <cassert>
#include <cmath>

// Author:  Douglas Wilhelm Harder
// Copyright (c) 2011 by Douglas Wilhelm Harder.  All rights reserved.

// On successive calls to Normal_distributions::Central_limit_theorem::randn(), this function returns
// a random standard normal value (a mean of zero and standard deviation of one).
//
// It generates twelve uniformly distributed values on the interval [0, 1], adds them, and subtracts
// six giving a reasonably close approximation to a standard normal.

namespace Normal_distributions {
	class Central_limit_theorem {
		public:
			static double randn();
	};

	double Central_limit_theorem::randn() {
		double u = 0.0;

		for ( int i = 0; i < 12; ++i ) {
			u += drand48();
		}

		return u - 6.0;
	}
}

#endif