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<title>Boost Random Number Library Variate Generator</title>
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<h1>Boost Random Number Library Variate Generator</h1>
<p>A random variate generator is used to join a random number generator
together with a random number distribution. Boost.Random provides a vast
choice of <a href="random-generators.html">generators</a> as well as
<a href="random-distributions.html">distributions</a> .</p>
<h2><a name="variate_generator" id="variate_generator">Class template
<code>variate_generator</code></a></h2>
<h3>Synopsis</h3>
<pre>
#include <<a href=
"../../boost/random/variate_generator.hpp">boost/random/variate_generator.hpp</a>>
template<class Engine, class Distribution>
class variate_generator
{
public:
typedef Engine engine_type;
typedef Distribution distribution_type;
typedef typename Distribution::result_type result_type;
variate_generator(Engine e, Distribution d);
result_type operator()();
template<class T>
result_type operator()(T value);
engine_value_type& engine();
const engine_value_type& engine() const;
result_type min() const;
result_type max() const;
};
</pre>
<h3>Description</h3>
<p>Instantations of class template <code>variate_generator</code> model a
<a href="random-concepts.html#number_generator">number generator</a>.</p>
<p>The argument for the template parameter <code>Engine</code> shall be of
the form U, U&, or U*, where U models a uniform random number
generator. Then, the member <code>engine_value_type</code> names U (not the
pointer or reference to U).</p>
<p>Specializations of <code>variate_generator</code> satisfy the
requirements of CopyConstructible. They also satisfy the requirements of
Assignable unless the template parameter Engine is of the form U&.</p>
<p>The complexity of all functions specified in this section is constant.
No function described in this section except the constructor throws an
exception.</p>
<pre>
variate_generator(engine_type eng, distribution_type d)
</pre>
<p><strong>Effects:</strong> Constructs a <code>variate_generator</code>
object with the associated uniform random number generator <code>eng</code>
and the associated random distribution <code>d</code>.<br>
<strong>Throws:</strong> If and what the copy constructor of Engine or
Distribution throws.</p>
<pre>
result_type operator()()
</pre>
<p><strong>Returns:</strong> <code>distribution()(e)</code><br>
<strong>Notes:</strong> The sequence of numbers produced by the uniform
random number generator <code>e</code>, s<sub>e</sub>, is obtained from the
sequence of numbers produced by the associated uniform random number
generator <code>eng</code>, s<sub>eng</sub>, as follows: Consider the
values of <code>numeric_limits<<em>T</em>>::is_integer</code> for
<code><em>T</em></code> both <code>Distribution::input_type</code> and
<code>engine_value_type::result_type</code>. If the values for both types
are <code>true</code>, then s<sub>e</sub> is identical to s<sub>eng</sub>.
Otherwise, if the values for both types are <code>false</code>, then the
numbers in s<sub>eng</sub> are divided by
<code>engine().max()-engine().min()</code> to obtain the numbers in
s<sub>e</sub>. Otherwise, if the value for
<code>engine_value_type::result_type</code> is <code>true</code> and the
value for <code>Distribution::input_type</code> is <code>false</code>, then
the numbers in s<sub>eng</sub> are divided by
<code>engine().max()-engine().min()+1</code> to obtain the numbers in
s<sub>e</sub>. Otherwise, the mapping from s<sub>eng</sub> to s<sub>e</sub>
is implementation-defined. In all cases, an implicit conversion from
<code>engine_value_type::result_type</code> to
<code>Distribution::input_type</code> is performed. If such a conversion
does not exist, the program is ill-formed.</p>
<pre>
template<class T> result_type operator()(T value)
</pre>
<p><strong>Returns:</strong> <code>distribution()(e, value)</code>. For the
semantics of <code>e</code>, see the description of
<code>operator()()</code>.</p>
<pre>
engine_value_type& engine()
</pre>
<p><strong>Returns:</strong> A reference to the associated uniform random
number generator.</p>
<pre>
const engine_value_type& engine() const
</pre>
<p><strong>Returns:</strong> A reference to the associated uniform random
number generator.</p>
<pre>
distribution_type& distribution()
</pre>
<p><strong>Returns:</strong> A reference to the associated random
distribution.</p>
<pre>
const distribution_type& distribution() const
</pre>
<p><strong>Returns:</strong> A reference to the associated random
distribution.</p>
<pre>
result_type min() const
</pre>
<p><strong>Precondition:</strong> <code>distribution().min()</code> is
well-formed<br>
<strong>Returns:</strong> <code>distribution().min()</code></p>
<pre>
result_type max() const
</pre>
<p><strong>Precondition:</strong> <code>distribution().max()</code> is
well-formed<br>
<strong>Returns:</strong> <code>distribution().max()</code></p>
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<p>Revised
<!--webbot bot="Timestamp" s-type="EDITED" s-format="%d %B, %Y" startspan -->05
December, 2006<!--webbot bot="Timestamp" endspan i-checksum="38516" --></p>
<p><i>Copyright © 2003-2004 <a href=
"http://www.boost.org/people/jens_maurer.htm">Jens Maurer</a></i></p>
<p><i>Distributed under the Boost Software License, Version 1.0. (See
accompanying file <a href="../../LICENSE_1_0.txt">LICENSE_1_0.txt</a> or
copy at <a href=
"http://www.boost.org/LICENSE_1_0.txt">http://www.boost.org/LICENSE_1_0.txt</a>)</i></p>
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