Improved names for arguments of Multi-normal. No functional changes.

git-svn-id: https://svn.apache.org/repos/asf/mahout/trunk@1409688 13f79535-47bb-0310-9956-ffa450edef68
KukumavMozolo · Nov 15, 2012 · a2375a3 · a2375a3
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commit a2375a3
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Showing 2 changed files with 19 additions and 3 deletions.
diff --git a/math/src/main/java/org/apache/mahout/math/stats/LogLikelihood.java b/math/src/main/java/org/apache/mahout/math/stats/LogLikelihood.java
@@ -121,8 +121,11 @@ public static double logLikelihoodRatio(long k11, long k12, long k21, long k22)
    * @return The root log-likelihood ratio
    * 
    * <p/>
-   * See discussion of raw vs. root LLR at 
-   * http://www.lucidimagination.com/search/document/6dc8709e65a7ced1/llr_scoring_question
+   * There is some more discussion here:
+   * http://mail-archives.apache.org/mod_mbox/mahout-user/201001.mbox/%[email protected]%3E
+   *
+   * And see the response to Wataru's comment here:
+   * http://tdunning.blogspot.com/2008/03/surprise-and-coincidence.html
    */
   public static double rootLogLikelihoodRatio(long k11, long k12, long k21, long k22) {
     double llr = logLikelihoodRatio(k11, k12, k21, k22);

diff --git a/math/src/test/java/org/apache/mahout/math/stats/LogLikelihoodTest.java b/math/src/test/java/org/apache/mahout/math/stats/LogLikelihoodTest.java
@@ -58,12 +58,25 @@ public void testLogLikelihood() throws Exception {
   }
 
   @Test
-  public void testRootLogLikelihood() throws Exception {
+  public void testRootLogLikelihood() {
     // positive where k11 is bigger than expected.
     assertTrue(LogLikelihood.rootLogLikelihoodRatio(904, 21060, 1144, 283012) > 0.0);
 
     // negative because k11 is lower than expected
     assertTrue(LogLikelihood.rootLogLikelihoodRatio(36, 21928, 60280, 623876) < 0.0);
+
+    assertEquals(Math.sqrt(2.772589), LogLikelihood.rootLogLikelihoodRatio(1, 0, 0, 1), 0.000001);
+    assertEquals(-Math.sqrt(2.772589), LogLikelihood.rootLogLikelihoodRatio(0, 1, 1, 0), 0.000001);
+    assertEquals(Math.sqrt(27.72589), LogLikelihood.rootLogLikelihoodRatio(10, 0, 0, 10), 0.00001);
+
+    assertEquals(Math.sqrt(39.33052), LogLikelihood.rootLogLikelihoodRatio(5, 1995, 0, 100000), 0.00001);
+    assertEquals(-Math.sqrt(39.33052), LogLikelihood.rootLogLikelihoodRatio(0, 100000, 5, 1995), 0.00001);
+
+    assertEquals(Math.sqrt(4730.737), LogLikelihood.rootLogLikelihoodRatio(1000, 1995, 1000, 100000), 0.001);
+    assertEquals(-Math.sqrt(4730.737), LogLikelihood.rootLogLikelihoodRatio(1000, 100000, 1000, 1995), 0.001);
+
+    assertEquals(Math.sqrt(5734.343), LogLikelihood.rootLogLikelihoodRatio(1000, 1000, 1000, 100000), 0.001);
+    assertEquals(Math.sqrt(5714.932), LogLikelihood.rootLogLikelihoodRatio(1000, 1000, 1000, 99000), 0.001);
   }
 
   @Test