Merge branch 'master' of https://git-wip-us.apache.org/repos/asf/commons-math

src/main/java/org/apache/commons/math3/stat/descriptive/DescriptiveStatistics.java

@@ -258,6 +258,18 @@ public class DescriptiveStatistics implements StatisticalSummary, Serializable {
         return stdDev;
     }
 
+    /**
+     * Returns the quadratic mean, a.k.a.
+     * <a href="http://mathworld.wolfram.com/Root-Mean-Square.html">
+     * root-mean-square</a> of the available values
+     * @return The quadratic mean or {@code Double.NaN} if no values
+     * have been added.
+     */
+    public double getQuadraticMean() {
+        final long n = getN();
+        return n > 0 ? FastMath.sqrt(getSumsq() / n) : Double.NaN;
+    }
+
     /**
      * Returns the skewness of the available values. Skewness is a
      * measure of the asymmetry of a given distribution.

src/main/java/org/apache/commons/math3/stat/descriptive/SummaryStatistics.java

@@ -224,6 +224,18 @@ public class SummaryStatistics implements StatisticalSummary, Serializable {
         return stdDev;
     }
 
+    /**
+     * Returns the quadratic mean, a.k.a.
+     * <a href="http://mathworld.wolfram.com/Root-Mean-Square.html">
+     * root-mean-square</a> of the available values
+     * @return The quadratic mean or {@code Double.NaN} if no values
+     * have been added.
+     */
+    public double getQuadraticMean() {
+        final long n = getN();
+        return n > 0 ? FastMath.sqrt(getSumsq() / n) : Double.NaN;
+    }
+
     /**
      * Returns the (sample) variance of the available values.
      *

src/main/java/org/apache/commons/math3/stat/descriptive/SynchronizedDescriptiveStatistics.java

@@ -114,6 +114,14 @@ public class SynchronizedDescriptiveStatistics extends DescriptiveStatistics {
         return super.getStandardDeviation();
     }
 
+    /**
+     * {@inheritDoc}
+     */
+    @Override
+    public synchronized double getQuadraticMean() {
+        return super.getQuadraticMean();
+    }
+
     /**
      * {@inheritDoc}
      */

src/main/java/org/apache/commons/math3/stat/descriptive/SynchronizedSummaryStatistics.java

@@ -111,6 +111,14 @@ public class SynchronizedSummaryStatistics extends SummaryStatistics {
         return super.getStandardDeviation();
     }
 
+    /**
+     * {@inheritDoc}
+     */
+    @Override
+    public synchronized double getQuadraticMean() {
+        return super.getQuadraticMean();
+    }
+
     /**
      * {@inheritDoc}
      */

src/test/java/org/apache/commons/math3/stat/descriptive/DescriptiveStatisticsTest.java

@@ -31,8 +31,6 @@ import org.junit.Test;
 
 /**
  * Test cases for the DescriptiveStatistics class.
- *
- *          2007) $
  */
 public class DescriptiveStatisticsTest {
 
@@ -106,6 +104,22 @@ public class DescriptiveStatisticsTest {
         Assert.assertEquals(12.0, stats.getElement(88), 1.0e-10);
     }
 
+    @Test
+    public void testQuadraticMean() {
+        final double[] values = { 1.2, 3.4, 5.6, 7.89 };
+        final DescriptiveStatistics stats = new DescriptiveStatistics(values);
+
+        final int len = values.length;
+        double expected = 0;
+        for (int i = 0; i < len; i++) {
+            final double v = values[i];
+            expected += v * v / len;
+        }
+        expected = Math.sqrt(expected);
+
+        Assert.assertEquals(expected, stats.getQuadraticMean(), Math.ulp(expected));
+    }
+
     @Test
     public void testToString() {
         DescriptiveStatistics stats = createDescriptiveStatistics();

src/test/java/org/apache/commons/math3/stat/descriptive/SummaryStatisticsTest.java

@@ -299,6 +299,23 @@ public class SummaryStatisticsTest {
         }
     }
     
+    @Test
+    public void testQuadraticMean() {
+        final double[] values = { 1.2, 3.4, 5.6, 7.89 };
+        final SummaryStatistics stats = createSummaryStatistics();
+
+        final int len = values.length;
+        double expected = 0;
+        for (int i = 0; i < len; i++) {
+            final double v = values[i];
+            expected += v * v / len;
+
+            stats.addValue(v);
+        }
+        expected = Math.sqrt(expected);
+
+        Assert.assertEquals(expected, stats.getQuadraticMean(), Math.ulp(expected));
+    }
     
     /**
      * JIRA: MATH-691