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<!DOCTYPE html>
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<title>dip::FastVarianceAccumulator class | DIPlib | a library for quantitative image analysis</title>
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<h1>
<div class="m-doc-include m-thin m-right-m m-text-right">
<a href="numeric.html" class="m-doc">Numeric algorithms and constants</a> module<br/><span class="m-code m-thin">#include <a href="file--diplib--accumulators-h.html">"diplib/accumulators.h"</a></span> </div>
<span class="m-breadcrumb"><a href="dip.html">dip</a>::<wbr/></span>FastVarianceAccumulator <span class="m-thin">class</span> </h1>
<p><code>FastVarianceAccumulator</code> computes mean and standard deviation by accumulating the sum of sample
values and the sum of the square of sample values.</p>
<div class="m-block m-default">
<h3>Contents</h3>
<ul>
<li>
Reference
<ul>
<li><a href="#function-members">Functions</a></li>
<li><a href="#operator-members">Operators</a></li>
<li><a href="#related">Related</a></li>
</ul>
</li>
</ul>
</div>
<p>Samples are added one by one, using the <code>Push</code> method. Other members are used to retrieve estimates of
the population statistics based on the samples seen up to that point. Formula used to compute population
statistics are corrected, though the standard deviation is not an unbiased estimator. The accumulator
uses a simple algorithm that could result in catastrophic cancellation if the variance is very small with
respect to the mean; use <a href="dip-VarianceAccumulator.html"><code>dip::VarianceAccumulator</code></a> to prevent it.</p>
<p>It is possible to accumulate samples in different objects (e.g. when processing with multiple threads),
and add the accumulators together using the <code>+</code> operator.</p>
<p>It is also possible to remove a sample from the accumulator, using the <code>Pop</code> method. It is assumed that the
particular value passed to this method had been added previously to the accumulator. If this is not the case,
resulting means and variances are no longer correct.</p>
<aside class="m-note m-default">
<h4>See also</h4>
<p><a href="dip-StatisticsAccumulator.html"><code>dip::StatisticsAccumulator</code></a>, <a href="dip-VarianceAccumulator.html"><code>dip::VarianceAccumulator</code></a>, <a href="dip-CovarianceAccumulator.html"><code>dip::CovarianceAccumulator</code></a>, <a href="dip-DirectionalStatisticsAccumulator.html"><code>dip::DirectionalStatisticsAccumulator</code></a>, <a href="dip-MinMaxAccumulator.html"><code>dip::MinMaxAccumulator</code></a>, <a href="dip-MomentAccumulator.html"><code>dip::MomentAccumulator</code></a></p>
</aside>
<section id="function-members">
<h2>Functions</h2>
<dl class="m-doc">
<dt id="dip-FastVarianceAccumulator-Reset">
<span class="m-doc-wrap-bumper">void <a href="#dip-FastVarianceAccumulator-Reset" class="m-doc-self">Reset</a>(</span><span class="m-doc-wrap">)</span>
</dt>
<dd>Reset the accumulator, leaving it as if newly allocated.</dd>
<dt id="dip-FastVarianceAccumulator-Push-dfloat-">
<span class="m-doc-wrap-bumper">void <a href="#dip-FastVarianceAccumulator-Push-dfloat-" class="m-doc-self">Push</a>(</span><span class="m-doc-wrap"><a href="pixeltypes.html#dip-dfloat" class="m-doc">dip::dfloat</a> x)</span>
</dt>
<dd>Add a sample to the accumulator</dd>
<dt id="dip-FastVarianceAccumulator-Pop-dfloat-">
<span class="m-doc-wrap-bumper">void <a href="#dip-FastVarianceAccumulator-Pop-dfloat-" class="m-doc-self">Pop</a>(</span><span class="m-doc-wrap"><a href="pixeltypes.html#dip-dfloat" class="m-doc">dip::dfloat</a> x)</span>
</dt>
<dd>Remove a sample from the accumulator</dd>
<dt id="dip-FastVarianceAccumulator-Number-C">
<span class="m-doc-wrap-bumper">auto <a href="#dip-FastVarianceAccumulator-Number-C" class="m-doc-self">Number</a>(</span><span class="m-doc-wrap">) const -> <a href="supporttypes.html#dip-uint" class="m-doc">dip::uint</a></span>
</dt>
<dd>Number of samples</dd>
<dt id="dip-FastVarianceAccumulator-Mean-C">
<span class="m-doc-wrap-bumper">auto <a href="#dip-FastVarianceAccumulator-Mean-C" class="m-doc-self">Mean</a>(</span><span class="m-doc-wrap">) const -> <a href="pixeltypes.html#dip-dfloat" class="m-doc">dip::dfloat</a></span>
</dt>
<dd>Unbiased estimator of population mean</dd>
<dt id="dip-FastVarianceAccumulator-Variance-C">
<span class="m-doc-wrap-bumper">auto <a href="#dip-FastVarianceAccumulator-Variance-C" class="m-doc-self">Variance</a>(</span><span class="m-doc-wrap">) const -> <a href="pixeltypes.html#dip-dfloat" class="m-doc">dip::dfloat</a></span>
</dt>
<dd>Unbiased estimator of population variance</dd>
<dt id="dip-FastVarianceAccumulator-StandardDeviation-C">
<span class="m-doc-wrap-bumper">auto <a href="#dip-FastVarianceAccumulator-StandardDeviation-C" class="m-doc-self">StandardDeviation</a>(</span><span class="m-doc-wrap">) const -> <a href="pixeltypes.html#dip-dfloat" class="m-doc">dip::dfloat</a></span>
</dt>
<dd>Estimator of population standard deviation (it is not possible to derive an unbiased estimator)</dd>
</dl>
</section>
<section id="operator-members">
<h2>Operators</h2>
<dl class="m-doc">
<dt id="dip-FastVarianceAccumulator-operator%2B%3D-FastVarianceAccumulator-CL">
<span class="m-doc-wrap-bumper">auto <a href="#dip-FastVarianceAccumulator-operator%2B%3D-FastVarianceAccumulator-CL" class="m-doc-self">operator+=</a>(</span><span class="m-doc-wrap"><a href="dip-FastVarianceAccumulator.html" class="m-doc">dip::FastVarianceAccumulator</a> const& b) -> <a href="dip-FastVarianceAccumulator.html" class="m-doc">dip::FastVarianceAccumulator</a>&</span>
</dt>
<dd>Combine two accumulators</dd>
</dl>
</section>
<section id="related">
<h2>Related</h2>
<dl class="m-doc">
<dt id="dip-operator%2B-FastVarianceAccumulator--FastVarianceAccumulator-CL">
<span class="m-doc-wrap-bumper">auto <a href="#dip-operator%2B-FastVarianceAccumulator--FastVarianceAccumulator-CL" class="m-doc-self">dip::<wbr />operator+</a>(</span><span class="m-doc-wrap"><a href="dip-FastVarianceAccumulator.html" class="m-doc">dip::FastVarianceAccumulator</a> lhs,
<a href="dip-FastVarianceAccumulator.html" class="m-doc">dip::FastVarianceAccumulator</a> const& rhs) -> <a href="dip-FastVarianceAccumulator.html" class="m-doc">dip::FastVarianceAccumulator</a></span>
</dt>
<dd>Combine two accumulators</dd>
</dl>
</section>
</div>
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