code: public static double ellipseCircum (double a, double b)
      {
          return Math.PI * (3*a + 3*b - Math.sqrt((a + 3*b) * (b + 3*a)));
      }
docs: Returns the approximate circumference of the ellipse defined by the specified minor and
  major axes. The formula used (due to Ramanujan, via a paper of his entitled "Modular
  Equations and Approximations to Pi"), is <code>Pi(3a + 3b - sqrt[(a+3b)(b+3a)])</code>.