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Added more content to statistics and distributions user guide. 

git-svn-id: https://svn.apache.org/repos/asf/jakarta/commons/proper/math/trunk@141113 13f79535-47bb-0310-9956-ffa450edef68
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Phil Steitz 2004-02-29 21:25:08 +00:00
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<document url="index.html">
<properties>
<title>The Commons Math User Guide - Table of Contents</title>
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<li><a href="overview.html#dependencies">0.5 Dependencies</a></li>
</ul></li>
<li><a href="stat.html">1. Statistics</a>
<li><a href="stat.html">1. Statistics and Distributions</a>
<ul>
<li><a href="stat.html#overview">1.1 Overview</a></li>
<li><a href="stat.html#univariate">1.2 Univariate statistics</a></li>

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<properties>
<title>The Commons Math User Guide - Statistics</title>
</properties>
<body>
<section name="1 Statistics">
<section name="1 Statistics and Distributions">
<subsection name="1.1 Overview" href="overview">
<p>This is yet to be written. Any contributions will be greatfully
accepted!</p>
<p>
The statistics and distributions packages provide frameworks and implementations for
basic univariate statistics, frequency distributions, bivariate regression, t- and chi-square test
statistics and some commonly used probability distributions.
</p>
</subsection>
<subsection name="1.2 Univariate statistics" href="univariate">
<p>This is yet to be written. Any contributions will be gratefully
accepted!</p>
<p>
The stat package includes a framework and default implementations for the following univariate
statistics:
<ul>
<li>arithmetic and geometric means</li>
<li>variance and standard deviation</li>
<li>sum, product, log sum, sum of squared values</li>
<li>minimum, maximum, median, and percentiles</li>
<li>skewness and kurtosis</li>
<li>first, second, third and fourth moments</li>
</ul>
</p>
<p>
With the exception of percentiles and the median, all of these statistics can be computed without
maintaining the full list of input data values in memory. The stat package provides interfaces and
implementations that do not require value storage as well as implementations that operate on arrays
of stored values.
</p>
<p>
The top level interface is
<a href="../apidocs/org/apache/commons/math/stat/univariate/UnivariateStatistic.html">
org.apache.commons.math.stat.univariate.UnivariateStatistic.</a> This interface, implemented by
all statistics, consists of <code>evaluate()</code> methods that take double[] arrays as arguments and return
the value of the statistic. This interface is extended by
<a href="../apidocs/org/apache/commons/math/stat/univariate/StorelessUnivariateStatistic.html">
org.apache.commons.math.stat.univariate.StorelessUnivariateStatistic,</a> which adds <code>increment(),</code>
<code>getResult()</code> and associated methods to support "storageless" implementations that
maintain counters, sums or other state information as values are added using the <code>increment()</code>
method.
</p>
<p>
Abstract implementations of the top level interfaces are provided in
<a href="../apidocs/org/apache/commons/math/stat/univariate/AbstractUnivariateStatistic.html">
org.apache.commons.math.stat.univariate.AbstractUnivariateStatistic</a> and
<a href="../apidocs/org/apache/commons/math/stat/univariate/AbstractStorelessUnivariateStatistic.html">
org.apache.commons.math.stat.univariate.AbstractStorelessUnivariateStatistic</a> respectively.
</p>
<p>
Each statistic is implemented as a separate class, in one of the subpackages (moment, rank, summary) and
each extends one of the abstract classes above (depending on whether or not value storage is required to
compute the statistic).
There are several ways to instantiate and use statistics. Statistics can be instantiated and used directly, but it is
generally more convenient to access them using the provided aggregates:
<table>
<tr><th>Aggregate</th><th>Statistics Included</th><th>Values stored?</th></tr>
<tr><td><a href="../apidocs/org/apache/commons/math/stat/DescriptiveStatistics.html">
org.apache.commons.math.stat.DescriptiveStatistics</a></td><td>All</td><td>Yes</td></tr>
<tr><td><a href="../apidocs/org/apache/commons/math/stat/SummaryStatistics.html">
org.apache.commons.math.stat.SummaryStatistics</a></td><td>min, max, mean, geometric mean, n, sum, sum of squares, standard deviation, variance</td><td>No</td></tr>
</table>
TODO: add code sample
There is also a utility class, <a href="../apidocs/org/apache/commons/math/stat/StatUtils.html">
org.apache.commons.math.stat.StatUtils,</a> that provides static methods for computing statistics
from double[] arrays.
</p>
</subsection>
<subsection name="1.3 Frequency distributions" href="frequency">
<p>This is yet to be written. Any contributions will be gratefully
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<tr><td>F</td><td>createFDistribution</td><td><div>Numerator degrees of freedom</div><div>Denominator degrees of freedom</div></td></tr>
<tr><td>Gamma</td><td>createGammaDistribution</td><td><div>Alpha</div><div>Beta</div></td></tr>
<tr><td>Hypergeometric</td><td>createHypogeometricDistribution</td><td><div>Population size</div><div>Number of successes in population</div><div>Sample size</div></td></tr>
<tr><td>Normal (Gaussian)</td><td>createNormalDistribution</td><td><div>Mean</div><div>Standard Deviation</div></td></tr>
<tr><td>t</td><td>createTDistribution</td><td><div>Degrees of freedom</div></td></tr>
</table>
</p>