private double search() {
		double l=mu-sigma*2;
		double r=mu+sigma*2;
		while (l+0.1<r){
			double t1=(r-l)/3+l;
			double t2=2*(r-l)/3+l;
			if(f(t1) < f(t2))
				l=t1;
			else r=t2;
		}
		return (l+r)/2;
	}