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  26 <a name="boost.accumulators.impl.lazy_rolling_variance_impl"></a><div class="titlepage"></div>
  27 <div class="refnamediv">
  28 <h2><span class="refentrytitle">Struct template lazy_rolling_variance_impl</span></h2>
  29 <p>boost::accumulators::impl::lazy_rolling_variance_impl &#8212; Immediate (lazy) calculation of the rolling variance. </p>
  30 </div>
  31 <h2 xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv-title">Synopsis</h2>
  32 <div xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv"><pre class="synopsis"><span class="comment">// In header: &lt;<a class="link" href="../../../accumulators/reference.html#header.boost.accumulators.statistics.rolling_variance_hpp" title="Header &lt;boost/accumulators/statistics/rolling_variance.hpp&gt;">boost/accumulators/statistics/rolling_variance.hpp</a>&gt;
  33
  34 </span><span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> Sample<span class="special">&gt;</span>
  35 <span class="keyword">struct</span> <a class="link" href="lazy_rolling_variance_impl.html" title="Struct template lazy_rolling_variance_impl">lazy_rolling_variance_impl</a> <span class="special">:</span> <span class="keyword">public</span> <span class="identifier">accumulator_base</span> <span class="special">{</span>
  36   <span class="comment">// types</span>
  37   <span class="keyword">typedef</span> <span class="identifier">numeric</span><span class="special">::</span><span class="identifier">functional</span><span class="special">::</span><span class="identifier">fdiv</span><span class="special">&lt;</span> <span class="identifier">Sample</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span><span class="special">,</span> <span class="keyword">void</span><span class="special">,</span> <span class="keyword">void</span> <span class="special">&gt;</span><span class="special">::</span><span class="identifier">result_type</span> <a name="boost.accumulators.impl.lazy_rolling_variance_impl.result_type"></a><span class="identifier">result_type</span><span class="special">;</span>
  38
  39   <span class="comment">// <a class="link" href="lazy_rolling_variance_impl.html#boost.accumulators.impl.lazy_rolling_variance_implconstruct-copy-destruct">construct/copy/destruct</a></span>
  40   <a class="link" href="lazy_rolling_variance_impl.html#idp66208640-bb"><span class="identifier">lazy_rolling_variance_impl</span></a><span class="special">(</span><span class="identifier">dont_care</span><span class="special">)</span><span class="special">;</span>
  41
  42   <span class="comment">// <a class="link" href="lazy_rolling_variance_impl.html#idp66205264-bb">public member functions</a></span>
  43   <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> Args<span class="special">&gt;</span> <span class="identifier">result_type</span> <a class="link" href="lazy_rolling_variance_impl.html#idp66205824-bb"><span class="identifier">result</span></a><span class="special">(</span><span class="identifier">Args</span> <span class="keyword">const</span> <span class="special">&amp;</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span>
  44 <span class="special">}</span><span class="special">;</span></pre></div>
  45 <div class="refsect1">
  46 <a name="idp104897664"></a><h2>Description</h2>
  47 <p>Calculation of sample variance <span class="inlinemediaobject"><img src="../../../images/accumulators//form_61.png"></span> is done as follows, see also <a href="http://en.wikipedia.org/wiki/Algorithms_for_calculating_variance" target="_top">http://en.wikipedia.org/wiki/Algorithms_for_calculating_variance</a>. For a rolling window of size <span class="inlinemediaobject"><img src="../../../images/accumulators//form_70.png"></span>, when <span class="inlinemediaobject"><img src="../../../images/accumulators//form_71.png"></span>, the variance is computed according to the formula </p>
  48 <div class="equation">
  49 <a name="idp104906416"></a><p class="title"><b>Equation&#160;1.7.&#160;</b></p>
  50 <div class="equation-contents"><div class="mediaobject" align="center"><img src="../../../images/accumulators//form_72.png" align="middle"></div></div>
  51 </div>
  52 <p><br class="equation-break"> When <span class="inlinemediaobject"><img src="../../../images/accumulators//form_73.png"></span>, the sample variance over the window becomes: </p>
  53 <div class="equation">
  54 <a name="idp104911776"></a><p class="title"><b>Equation&#160;1.8.&#160;</b></p>
  55 <div class="equation-contents"><div class="mediaobject" align="center"><img src="../../../images/accumulators//form_74.png" align="middle"></div></div>
  56 </div>
  57 <p><br class="equation-break"> </p>
  58 <div class="refsect2">
  59 <a name="idp104914656"></a><h3>
  60 <a name="boost.accumulators.impl.lazy_rolling_variance_implconstruct-copy-destruct"></a><code class="computeroutput">lazy_rolling_variance_impl</code>
  61         public
  62        construct/copy/destruct</h3>
  63 <div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"><pre class="literallayout"><a name="idp66208640-bb"></a><span class="identifier">lazy_rolling_variance_impl</span><span class="special">(</span><span class="identifier">dont_care</span><span class="special">)</span><span class="special">;</span></pre></li></ol></div>
  64 </div>
  65 <div class="refsect2">
  66 <a name="idp104921248"></a><h3>
  67 <a name="idp66205264-bb"></a><code class="computeroutput">lazy_rolling_variance_impl</code> public member functions</h3>
  68 <div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"><pre class="literallayout"><span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> Args<span class="special">&gt;</span> <span class="identifier">result_type</span> <a name="idp66205824-bb"></a><span class="identifier">result</span><span class="special">(</span><span class="identifier">Args</span> <span class="keyword">const</span> <span class="special">&amp;</span> args<span class="special">)</span> <span class="keyword">const</span><span class="special">;</span></pre></li></ol></div>
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  74 <td align="right"><div class="copyright-footer">Copyright &#169; 2005, 2006 Eric Niebler<p>
  75         Distributed under the Boost Software License, Version 1.0. (See accompanying
  76         file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
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