Added geometric mean to StatUtils.

git-svn-id: https://svn.apache.org/repos/asf/jakarta/commons/proper/math/trunk@141392 13f79535-47bb-0310-9956-ffa450edef68

src/java/org/apache/commons/math/stat/StatUtils.java

@@ -16,6 +16,7 @@
 package org.apache.commons.math.stat;
 
 import org.apache.commons.math.stat.univariate.UnivariateStatistic;
+import org.apache.commons.math.stat.univariate.moment.GeometricMean;
 import org.apache.commons.math.stat.univariate.moment.Mean;
 import org.apache.commons.math.stat.univariate.moment.Variance;
 import org.apache.commons.math.stat.univariate.rank.Max;
@@ -30,7 +31,7 @@ import org.apache.commons.math.stat.univariate.summary.SumOfSquares;
  * StatUtils provides static methods for computing statistics based on data
  * stored in double[] arrays. 
  * 
- * @version $Revision: 1.30 $ $Date: 2004/07/11 18:41:19 $
+ * @version $Revision: 1.31 $ $Date: 2004/07/17 22:01:39 $
  */
 public final class StatUtils {
 
@@ -58,8 +59,11 @@ public final class StatUtils {
     /** variance */
     private static Variance variance = new Variance();
 
-    /** variance */
+    /** percentile */
     private static Percentile percentile = new Percentile();
+    
+    /** geometric mean */
+    private static GeometricMean geometricMean = new GeometricMean();
 
     /**
      * Private Constructor
@@ -246,6 +250,46 @@ public final class StatUtils {
             final int length) {
         return mean.evaluate(values, begin, length);
     }
+    
+    /**
+     * Returns the geometric mean of the entries in the input array, or 
+     * <code>Double.NaN</code> if the array is empty.
+     * <p>
+     * Throws <code>IllegalArgumentException</code> if the array is null.
+     * <p>
+     * See {@link org.apache.commons.math.stat.univariate.moment.GeometricMean}
+     * for details on the computing algorithm.
+     * 
+     * @param values the input array
+     * @return the geometric mean of the values or Double.NaN if the array is empty
+     * @throws IllegalArgumentException if the array is null
+     */
+    public static double geometricMean(final double[] values) {
+        return geometricMean.evaluate(values);
+    }
+
+    /**
+     * Returns the geometric mean of the entries in the specified portion of
+     * the input array, or <code>Double.NaN</code> if the designated subarray
+     * is empty.
+     * <p>
+     * Throws <code>IllegalArgumentException</code> if the array is null.
+     * <p>
+     * See {@link org.apache.commons.math.stat.univariate.moment.GeometricMean}
+     * for details on the computing algorithm.
+     * 
+     * @param values the input array
+     * @param begin index of the first array element to include
+     * @param length the number of elements to include
+     * @return the geometric mean of the values or Double.NaN if length = 0
+     * @throws IllegalArgumentException if the array is null or the array index
+     * parameters are not valid
+     */
+    public static double geometricMean(final double[] values, final int begin,
+            final int length) {
+        return geometricMean.evaluate(values, begin, length);
+    }
+    
 
     /**
      * Returns the variance of the entries in the input array, or 

src/test/org/apache/commons/math/stat/StatUtilsTest.java

@@ -23,7 +23,7 @@ import org.apache.commons.math.TestUtils;
 
 /**
  * Test cases for the {@link StatUtils} class.
- * @version $Revision: 1.18 $ $Date: 2004/07/11 18:42:07 $
+ * @version $Revision: 1.19 $ $Date: 2004/07/17 22:01:39 $
  */
 
 public final class StatUtilsTest extends TestCase {
@@ -372,4 +372,17 @@ public final class StatUtilsTest extends TestCase {
             // expected
         }
     }
+    
+    public void testGeometricMean() throws Exception {
+        double[] test = null;
+        try {
+            double x = StatUtils.geometricMean(test);
+            fail("Expecting IllegalArgumentException");
+        } catch (IllegalArgumentException ex) {
+            // expected
+        }
+        test = new double[] {2, 4, 6, 8};
+        assertEquals(Math.exp(0.25d * StatUtils.sumLog(test)), 
+                StatUtils.geometricMean(test), Double.MIN_VALUE);
+    }
 }