Added Ramanujan's formula for an approximation of the circumference of an

ellipse. I didn't end up using it in the ArcPath, but it will surely come
in handy eventually.


git-svn-id: svn+ssh://src.earth.threerings.net/narya/trunk@1690 542714f4-19e9-0310-aa3c-eee0fc999fb1

src/java/com/threerings/media/util/MathUtil.java

@@ -1,5 +1,5 @@
 //
-// $Id: MathUtil.java,v 1.4 2002/05/17 21:13:03 mdb Exp $
+// $Id: MathUtil.java,v 1.5 2002/09/17 04:00:09 mdb Exp $
 
 package com.threerings.media.util;
 
@@ -45,4 +45,15 @@ public class MathUtil
     {
 	return lineToString(p1.x, p1.y, p2.x, p2.y);
     }
+
+    /**
+     * 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>.
+     */
+    public static double ellipseCircum (double a, double b)
+    {
+        return Math.PI * (3*a + 3*b - Math.sqrt((a + 3*b) * (b + 3*a)));
+    }
 }