MyMath: add the "phi" constant

Author: stephengold

src/main/java/jme3utilities/math/MyMath.java

@@ -42,6 +42,10 @@ public class MyMath {
     // *************************************************************************
     // constants and loggers
 
+    /**
+     * golden ratio = 1.618...
+     */
+    final public static float phi = (1f + FastMath.sqrt(5f)) / 2f;
     /**
      * square root of 1/2
      */