[Jmol-commits] SF.net SVN: jmol:[12597] trunk/Jmol/src/org/jmol/util/Quaternion.java

[<ha...@us...>]

Revision: 12597
          http://jmol.svn.sourceforge.net/jmol/?rev=12597&view=rev
Author:   hansonr
Date:     2010-03-11 13:01:44 +0000 (Thu, 11 Mar 2010)

Log Message:
-----------
version=11.9.33_dev # new feature: quaterion array  .average .stddev  using SphereMean

Modified Paths:
--------------
    trunk/Jmol/src/org/jmol/util/Quaternion.java

Modified: trunk/Jmol/src/org/jmol/util/Quaternion.java
===================================================================
--- trunk/Jmol/src/org/jmol/util/Quaternion.java	2010-03-11 12:53:32 UTC (rev 12596)
+++ trunk/Jmol/src/org/jmol/util/Quaternion.java	2010-03-11 13:01:44 UTC (rev 12597)
@@ -739,6 +739,11 @@
     return dqMean.mul(mean);
   }
 
+  /**
+   * @param data
+   * @param mean
+   * @return     standard deviation in units of degrees
+   */
   private static float stdDev(Quaternion[] data, Quaternion mean) {
     double sum = 0;
     double sum2 = 0;
@@ -747,9 +752,10 @@
     // that is, cos(theta/2) for theta between them
     
     for (int i = n; --i >= 0;) {
-      float dist = 2 * (float) Math.acos(data[i].dot(mean));
-      sum += dist;
-      sum2 += dist * dist;
+      Quaternion dq = data[i].div(mean);
+      float theta = dq.getTheta();
+      sum += theta;
+      sum2 += theta * theta;
     }
     sum2 = sum2 - sum * sum / n;
     if (sum2 < 0)


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