From 3f5862a60e1045427b95fa44fdddfb0d4c11a771 Mon Sep 17 00:00:00 2001
From: Phil Steitz <psteitz@apache.org>
Date: Wed, 1 Sep 2004 15:54:39 +0000
Subject: [PATCH] Made assumption about precomputed mean explicit in javadoc. 
 Added missing method.

git-svn-id: https://svn.apache.org/repos/asf/jakarta/commons/proper/math/trunk@141437 13f79535-47bb-0310-9956-ffa450edef68
---
 .../univariate/moment/StandardDeviation.java  | 33 ++++++++++++++++++-
 1 file changed, 32 insertions(+), 1 deletion(-)

diff --git a/src/java/org/apache/commons/math/stat/univariate/moment/StandardDeviation.java b/src/java/org/apache/commons/math/stat/univariate/moment/StandardDeviation.java
index a47065036..72844356a 100644
--- a/src/java/org/apache/commons/math/stat/univariate/moment/StandardDeviation.java
+++ b/src/java/org/apache/commons/math/stat/univariate/moment/StandardDeviation.java
@@ -30,7 +30,7 @@ import org.apache.commons.math.stat.univariate.AbstractStorelessUnivariateStatis
  * one of the threads invokes the <code>increment()</code> or 
  * <code>clear()</code> method, it must be synchronized externally.
  * 
- * @version $Revision: 1.22 $ $Date: 2004/07/18 04:42:02 $
+ * @version $Revision: 1.23 $ $Date: 2004/09/01 15:54:39 $
  */
 public class StandardDeviation extends AbstractStorelessUnivariateStatistic
     implements Serializable {
@@ -133,6 +133,11 @@ public class StandardDeviation extends AbstractStorelessUnivariateStatistic
      * <p>
      * Returns 0 for a single-value (i.e. length = 1) sample.
      * <p>
+     * The formula used assumes that the supplied mean value is the arithmetic
+     * mean of the sample data, not a known population parameter.  This method
+     * is supplied only to save computation when the mean has already been
+     * computed.
+     * <p>
      * Throws <code>IllegalArgumentException</code> if the array is null.
      * <p>
      * Does not change the internal state of the statistic.
@@ -149,4 +154,30 @@ public class StandardDeviation extends AbstractStorelessUnivariateStatistic
             final int begin, final int length)  {
         return Math.sqrt(variance.evaluate(values, mean, begin, length));
     }
+    
+    /**
+     * Returns the Standard Deviation of the entries in the input array, using
+     * the precomputed mean value.  Returns
+     * <code>Double.NaN</code> if the designated subarray is empty.
+     * <p>
+     * Returns 0 for a single-value (i.e. length = 1) sample.
+     * <p>
+     * The formula used assumes that the supplied mean value is the arithmetic
+     * mean of the sample data, not a known population parameter.  This method
+     * is supplied only to save computation when the mean has already been
+     * computed.
+     * <p>
+     * Throws <code>IllegalArgumentException</code> if the array is null.
+     * <p>
+     * Does not change the internal state of the statistic.
+     * 
+     * @param values the input array
+     * @param mean the precomputed mean value
+     * @return the standard deviation 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 double evaluate(final double[] values, final double mean)  {
+        return Math.sqrt(variance.evaluate(values, mean));
+    }
 }
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