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<title>Boost Random Number Library Variate Generator</title>
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<h1>Boost Random Number Library Variate Generator</h1>
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>
.
<h2><a name="variate_generator">Class template <code>variate_generator</code></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>
Instantations of class template <code>variate_generator</code> model a
<a href="random-concepts.html#number_generator">number generator</a>.
<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>
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>
The complexity of all functions specified in this section is
constant. No function described in this section except the constructor
throws an exception.
<pre> variate_generator(engine_type eng, distribution_type d)</pre>
<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.
<pre> result_type operator()()</pre>
<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.
<pre> template<class T> result_type operator()(T value)</pre>
<strong>Returns:</strong> <code>distribution()(e, value)</code>. For
the semantics of <code>e</code>, see the description of
<code>operator()()</code>.
<pre> engine_value_type& engine()</pre>
<strong>Returns:</strong> A reference to the associated uniform random
number generator.
<pre> const engine_value_type& engine() const</pre>
<strong>Returns:</strong> A reference to the associated uniform random
number generator.
<pre> distribution_type& distribution()</pre>
<strong>Returns:</strong> A reference to the associated random
distribution.
<pre> const distribution_type& distribution() const</pre>
<strong>Returns:</strong> A reference to the associated random
distribution.
<pre> result_type min() const</pre>
<strong>Precondition:</strong> <code>distribution().min()</code> is
well-formed
<br>
<strong>Returns:</strong> <code>distribution().min()</code>
<pre> result_type max() const</pre>
<strong>Precondition:</strong> <code>distribution().max()</code> is
well-formed
<br>
<strong>Returns:</strong> <code>distribution().max()</code>
<p>
<hr>
<a href="../../people/jens_maurer.htm">Jens Maurer</a>,
2003-10-25
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