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<div class="titlepage"><div><div><h4 class="title">
<a name="math_toolkit.dist.stat_tut.variates"></a><a class="link" href="variates.html" title="Random Variates and Distribution Parameters"> Random Variates
and Distribution Parameters</a>
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<p>
<a href="http://en.wikipedia.org/wiki/Random_variate" target="_top">Random variates</a>
and <a href="http://en.wikipedia.org/wiki/Parameter" target="_top">distribution parameters</a>
are conventionally distinguished (for example in Wikipedia and Wolfram
MathWorld by placing a semi-colon after the random variate (whose value
you 'choose'), to separate the variate from the parameter(s) that defines
the shape of the distribution.
</p>
<p>
For example, the binomial distribution has two parameters: n (the number
of trials) and p (the probability of success on one trial). It also has
the random variate <span class="emphasis"><em>k</em></span>: the number of successes observed.
This means the probability density/mass function (pdf) is written as <span class="emphasis"><em>f(k;
n, p)</em></span>.
</p>
<p>
Translating this into code the <code class="computeroutput"><span class="identifier">binomial_distribution</span></code>
constructor therefore has two parameters:
</p>
<pre class="programlisting"><span class="identifier">binomial_distribution</span><span class="special">(</span><span class="identifier">RealType</span> <span class="identifier">n</span><span class="special">,</span> <span class="identifier">RealType</span> <span class="identifier">p</span><span class="special">);</span>
</pre>
<p>
While the function <code class="computeroutput"><span class="identifier">pdf</span></code>
has one argument specifying the distribution type (which includes it's
parameters, if any), and a second argument for the random variate. So taking
our binomial distribution example, we would write:
</p>
<pre class="programlisting"><span class="identifier">pdf</span><span class="special">(</span><span class="identifier">binomial_distribution</span><span class="special"><</span><span class="identifier">RealType</span><span class="special">>(</span><span class="identifier">n</span><span class="special">,</span> <span class="identifier">p</span><span class="special">),</span> <span class="identifier">k</span><span class="special">);</span>
</pre>
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<td align="right"><div class="copyright-footer">Copyright © 2006 , 2007, 2008, 2009 John Maddock, Paul A. Bristow,
Hubert Holin, Xiaogang Zhang, Bruno Lalande, Johan Råde, Gautam Sewani
and Thijs van den Berg<p>
Distributed under the Boost Software License, Version 1.0. (See accompanying
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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