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From pste...@apache.org
Subject cvs commit: jakarta-commons/math/src/java/org/apache/commons/math/stat/univariate/moment Mean.java
Date Fri, 02 Jul 2004 13:59:49 GMT
psteitz     2004/07/02 06:59:49

  Modified:    math/src/java/org/apache/commons/math/stat/univariate/moment
                        Mean.java
  Log:
  Made Sum instance local to evaluate. Improved javadoc.
  
  Revision  Changes    Path
  1.19      +46 -25    jakarta-commons/math/src/java/org/apache/commons/math/stat/univariate/moment/Mean.java
  
  Index: Mean.java
  ===================================================================
  RCS file: /home/cvs/jakarta-commons/math/src/java/org/apache/commons/math/stat/univariate/moment/Mean.java,v
  retrieving revision 1.18
  retrieving revision 1.19
  diff -u -r1.18 -r1.19
  --- Mean.java	23 Jun 2004 16:26:15 -0000	1.18
  +++ Mean.java	2 Jul 2004 13:59:49 -0000	1.19
  @@ -17,38 +17,60 @@
   
   import java.io.Serializable;
   
  -import org
  -    .apache
  -    .commons
  -    .math
  -    .stat
  -    .univariate
  -    .AbstractStorelessUnivariateStatistic;
  +import org.apache.commons.math.stat.univariate.AbstractStorelessUnivariateStatistic;
   import org.apache.commons.math.stat.univariate.summary.Sum;
   
   /**
  - * Returns the <a href="http://www.xycoon.com/arithmetic_mean.htm">
  - * arithmetic mean </a> of the available values.
  + * Returns the arithmetic mean of the available values. Uses the definitional 
  + * formula:
  + * <p>
  + * mean = sum(x_i) / n
  + * <p>
  + * where <code>n</code> is the number of observations.
  + * <p>
  + * The value of the statistic is computed using the following recursive
  + * updating algorithm:
  + * <p>
  + * <ol>
  + * <li>Initialize <code>m = </code> the first value</li>
  + * <li>For each additional value, update using <br>
  + *   <code>m = m + (new value - m) / (number of observations)</code></li>
  + * </ol>
  + * <p>
  + *  Returns <code>Double.NaN</code> if the dataset is empty.
  + * <p>
  + * <strong>Note that this implementation is not synchronized.</strong> If 
  + * multiple threads access an instance of this class concurrently, and at least
  + * one of the threads invokes the <code>increment()</code>, or 
  + * <code>clear()</code> method,  it must be synchronized externally.
  + * 
    * @version $Revision$ $Date$
    */
  -public class Mean extends AbstractStorelessUnivariateStatistic implements Serializable{
  +public class Mean extends AbstractStorelessUnivariateStatistic 
  +    implements Serializable {
   
       /** Serializable version identifier */
       static final long serialVersionUID = -1296043746617791564L;    
       
  -    /** first moment of values that have been added */
  +    /** First moment on which this statistic is based. */
       protected FirstMoment moment = null;
   
  -    /** */
  +    /** 
  +     * Determines whether or not this statistic can be incremented or cleared.
  +     * <p>
  +     * Statistics based on (constructed from) external moments cannot
  +     * be incremented or cleared.
  +     */
       protected boolean incMoment = true;
   
  -    /** */
  +    /** Constructs a Mean. */
       public Mean() {
           moment = new FirstMoment();
       }
   
       /**
        * Constructs a Mean with an External Moment.
  +     * 
        * @param m1 the moment
        */
       public Mean(final FirstMoment m1) {
  @@ -87,26 +109,25 @@
       public double getN() {
           return moment.getN();
       }
  -    
  -    /*UnvariateStatistic Approach */
  -
  -    /** */
  -    protected Sum sum = new Sum();
   
       /**
  -     * Returns the <a href="http://www.xycoon.com/arithmetic_mean.htm">
  -     * arithmetic mean </a> of a double[] of the available values.
  +     * Returns the arithmetic mean of the values 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 Mean} for details on the computing algorithm.
  +     * 
        * @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 mean of the values or Double.NaN if the array is empty
  +     * @throws IllegalArgumentException if the array is null
        * @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) {
           if (test(values, begin, length)) {
  +            Sum sum = new Sum();
               return sum.evaluate(values, begin, length) / ((double) length);
           }
           return Double.NaN;
  
  
  

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