算平方根 (方法)

public static double sqr(double square) {
  double x0, x1;
  double k = 0.0000001;// 精度
  x0 = 0.3 * square;
  x1 = 0.5 * (x0 + square / x0);
  while (x0 - x1 > k) {
   x0 = x1;
   x1 = 0.5 * (x0 + square / x0);
  }
  return (x0 + x1) / 2;
 }