double ternary_search(double l, double r) {
	double eps = 1e-9;              //set the error limit here
	while (r - l > eps) {
		double m1 = l + (r - l) / 3;
		double m2 = r - (r - l) / 3;
		double f1 = f(m1);      //evaluates the function at m1
		double f2 = f(m2);      //evaluates the function at m2
		if (f1 < f2)
			l = m1;
		else
			r = m2;
	}
	return f(l);                    //return the maximum of f(x) in [l, r]
}