Improved efficiency and javadoc.

git-svn-id: https://svn.apache.org/repos/asf/jakarta/commons/proper/math/trunk@141314 13f79535-47bb-0310-9956-ffa450edef68

src/java/org/apache/commons/math/stat/univariate/summary/SumOfLogs.java

@@ -17,45 +17,41 @@ package org.apache.commons.math.stat.univariate.summary;
 
 import java.io.Serializable;
 
-import org
-    .apache
-    .commons
-    .math
-    .stat
-    .univariate
-    .AbstractStorelessUnivariateStatistic;
+import org.apache.commons.math.stat.univariate.AbstractStorelessUnivariateStatistic;
 
 /**
- * Returns the sum of the natural logs for this collection of values.
+ * Returns the sum of the natural logs for this collection of values.  
+ * <p>
+ * Uses {@link java.lang.Math#log(double)} to compute the logs.  Therefore,
+ * <ul>
+ * <li>If any of values are < 0, the result is <code>NaN.</code></li>
+ * <li>If all values are non-negative and less than <code>Double.POSITIVE_INFINITY</code>, 
+ * but at least one value is 0, the result is <code>Double.NEGATIVE_INFINITY.</code></li>
+ * <li>If both <code>Double.POSITIVE_INFINITY</code> and 
+ * <code>Double.NEGATIVE_INFINITY</code> are among the values, the result is
+ * <code>NaN.</code></li>
+ * </ul>
  * 
- * @version $Revision: 1.17 $ $Date: 2004/04/27 16:42:32 $
+ * @version $Revision: 1.18 $ $Date: 2004/06/18 06:32:07 $
  */
 public class SumOfLogs extends AbstractStorelessUnivariateStatistic implements Serializable {
 
     /** Serializable version identifier */
     static final long serialVersionUID = -370076995648386763L;    
 
-    /** */
+    /**Number of values that have been added */
     private int n = 0;
     
     /**
      * The currently running value
      */
-    private double value = Double.NaN;
-
-    /** */
-    private boolean init = true;
+    private double value = 0d;
 
     /**
      * @see org.apache.commons.math.stat.univariate.StorelessUnivariateStatistic#increment(double)
      */
     public void increment(final double d) {
-        if (init) {
-            value = Math.log(d);
-            init = false;
-        } else {
-            value += Math.log(d);
-        }
+        value += Math.log(d);
         n++;
     }
 
@@ -63,7 +59,11 @@ public class SumOfLogs extends AbstractStorelessUnivariateStatistic implements S
      * @see org.apache.commons.math.stat.univariate.StorelessUnivariateStatistic#getResult()
      */
     public double getResult() {
-        return value;
+        if (n > 0) {
+            return value;
+        } else {
+            return Double.NaN;
+        }
     }
 
     /**
@@ -77,23 +77,22 @@ public class SumOfLogs extends AbstractStorelessUnivariateStatistic implements S
      * @see org.apache.commons.math.stat.univariate.StorelessUnivariateStatistic#clear()
      */
     public void clear() {
-        value = Double.NaN;
-        init = true;
+        value = 0d;
         n = 0;
     }
 
     /**
-     * Returns the sum of the natural logs for this collection of values
+     * Returns the sum of the natural logs for this collection of values.
+     * <p>
+     * See {@link SumOfLogs}.
+     * 
      * @param values Is a double[] containing the values
      * @param begin processing at this point in the array
      * @param length the number of elements to include
      * @return the sumLog value or Double.NaN if the array is empty
      * @see org.apache.commons.math.stat.univariate.UnivariateStatistic#evaluate(double[], int, int)
      */
-    public double evaluate(
-        final double[] values,
-        final int begin,
-        final int length) {
+    public double evaluate(final double[] values, final int begin, final int length) {
         double sumLog = Double.NaN;
         if (test(values, begin, length)) {
             sumLog = 0.0;