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| 7 | |
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| 8 | <title>Boost Random Number Library Variate Generator</title> |
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| 9 | </head> |
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| 10 | |
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| 11 | <body bgcolor="#FFFFFF" text="#000000"> |
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| 12 | <h1>Boost Random Number Library Variate Generator</h1> |
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| 13 | |
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| 14 | <p>A random variate generator is used to join a random number generator |
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| 15 | together with a random number distribution. Boost.Random provides a vast |
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| 16 | choice of <a href="random-generators.html">generators</a> as well as |
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| 17 | <a href="random-distributions.html">distributions</a> .</p> |
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| 18 | |
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| 19 | <h2><a name="variate_generator" id="variate_generator">Class template |
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| 20 | <code>variate_generator</code></a></h2> |
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| 21 | |
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| 22 | <h3>Synopsis</h3> |
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| 23 | <pre> |
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| 24 | #include <<a href= |
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| 25 | "../../boost/random/variate_generator.hpp">boost/random/variate_generator.hpp</a>> |
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| 26 | |
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| 27 | template<class Engine, class Distribution> |
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| 28 | class variate_generator |
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| 29 | { |
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| 30 | public: |
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| 31 | typedef Engine engine_type; |
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| 32 | typedef Distribution distribution_type; |
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| 33 | typedef typename Distribution::result_type result_type; |
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| 34 | |
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| 35 | variate_generator(Engine e, Distribution d); |
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| 36 | |
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| 37 | result_type operator()(); |
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| 38 | template<class T> |
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| 39 | result_type operator()(T value); |
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| 40 | |
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| 41 | engine_value_type& engine(); |
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| 42 | const engine_value_type& engine() const; |
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| 43 | |
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| 44 | result_type min() const; |
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| 45 | result_type max() const; |
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| 46 | }; |
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| 47 | </pre> |
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| 48 | |
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| 49 | <h3>Description</h3> |
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| 50 | |
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| 51 | <p>Instantations of class template <code>variate_generator</code> model a |
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| 52 | <a href="random-concepts.html#number_generator">number generator</a>.</p> |
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| 53 | |
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| 54 | <p>The argument for the template parameter <code>Engine</code> shall be of |
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| 55 | the form U, U&, or U*, where U models a uniform random number |
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| 56 | generator. Then, the member <code>engine_value_type</code> names U (not the |
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| 57 | pointer or reference to U).</p> |
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| 58 | |
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| 59 | <p>Specializations of <code>variate_generator</code> satisfy the |
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| 60 | requirements of CopyConstructible. They also satisfy the requirements of |
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| 61 | Assignable unless the template parameter Engine is of the form U&.</p> |
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| 62 | |
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| 63 | <p>The complexity of all functions specified in this section is constant. |
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| 64 | No function described in this section except the constructor throws an |
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| 65 | exception.</p> |
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| 66 | <pre> |
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| 67 | variate_generator(engine_type eng, distribution_type d) |
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| 68 | </pre> |
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| 69 | |
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| 70 | <p><strong>Effects:</strong> Constructs a <code>variate_generator</code> |
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| 71 | object with the associated uniform random number generator <code>eng</code> |
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| 72 | and the associated random distribution <code>d</code>.<br> |
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| 73 | <strong>Throws:</strong> If and what the copy constructor of Engine or |
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| 74 | Distribution throws.</p> |
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| 75 | <pre> |
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| 76 | result_type operator()() |
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| 77 | </pre> |
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| 78 | |
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| 79 | <p><strong>Returns:</strong> <code>distribution()(e)</code><br> |
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| 80 | <strong>Notes:</strong> The sequence of numbers produced by the uniform |
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| 81 | random number generator <code>e</code>, s<sub>e</sub>, is obtained from the |
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| 82 | sequence of numbers produced by the associated uniform random number |
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| 83 | generator <code>eng</code>, s<sub>eng</sub>, as follows: Consider the |
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| 84 | values of <code>numeric_limits<<em>T</em>>::is_integer</code> for |
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| 85 | <code><em>T</em></code> both <code>Distribution::input_type</code> and |
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| 86 | <code>engine_value_type::result_type</code>. If the values for both types |
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| 87 | are <code>true</code>, then s<sub>e</sub> is identical to s<sub>eng</sub>. |
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| 88 | Otherwise, if the values for both types are <code>false</code>, then the |
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| 89 | numbers in s<sub>eng</sub> are divided by |
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| 90 | <code>engine().max()-engine().min()</code> to obtain the numbers in |
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| 91 | s<sub>e</sub>. Otherwise, if the value for |
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| 92 | <code>engine_value_type::result_type</code> is <code>true</code> and the |
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| 93 | value for <code>Distribution::input_type</code> is <code>false</code>, then |
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| 94 | the numbers in s<sub>eng</sub> are divided by |
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| 95 | <code>engine().max()-engine().min()+1</code> to obtain the numbers in |
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| 96 | s<sub>e</sub>. Otherwise, the mapping from s<sub>eng</sub> to s<sub>e</sub> |
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| 97 | is implementation-defined. In all cases, an implicit conversion from |
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| 98 | <code>engine_value_type::result_type</code> to |
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| 99 | <code>Distribution::input_type</code> is performed. If such a conversion |
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| 100 | does not exist, the program is ill-formed.</p> |
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| 101 | <pre> |
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| 102 | template<class T> result_type operator()(T value) |
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| 103 | </pre> |
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| 104 | |
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| 105 | <p><strong>Returns:</strong> <code>distribution()(e, value)</code>. For the |
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| 106 | semantics of <code>e</code>, see the description of |
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| 107 | <code>operator()()</code>.</p> |
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| 108 | <pre> |
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| 109 | engine_value_type& engine() |
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| 110 | </pre> |
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| 111 | |
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| 112 | <p><strong>Returns:</strong> A reference to the associated uniform random |
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| 113 | number generator.</p> |
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| 114 | <pre> |
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| 115 | const engine_value_type& engine() const |
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| 116 | </pre> |
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| 117 | |
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| 118 | <p><strong>Returns:</strong> A reference to the associated uniform random |
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| 119 | number generator.</p> |
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| 120 | <pre> |
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| 121 | distribution_type& distribution() |
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| 122 | </pre> |
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| 123 | |
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| 124 | <p><strong>Returns:</strong> A reference to the associated random |
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| 125 | distribution.</p> |
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| 126 | <pre> |
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| 127 | const distribution_type& distribution() const |
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| 128 | </pre> |
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| 129 | |
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| 130 | <p><strong>Returns:</strong> A reference to the associated random |
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| 131 | distribution.</p> |
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| 132 | <pre> |
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| 133 | result_type min() const |
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| 134 | </pre> |
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| 135 | |
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| 136 | <p><strong>Precondition:</strong> <code>distribution().min()</code> is |
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| 137 | well-formed<br> |
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| 138 | <strong>Returns:</strong> <code>distribution().min()</code></p> |
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| 139 | <pre> |
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| 140 | result_type max() const |
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| 141 | </pre> |
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| 142 | |
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| 143 | <p><strong>Precondition:</strong> <code>distribution().max()</code> is |
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| 144 | well-formed<br> |
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| 145 | <strong>Returns:</strong> <code>distribution().max()</code></p> |
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| 146 | <hr> |
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| 147 | |
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| 148 | <p><a href="http://validator.w3.org/check?uri=referer"><img border="0" src= |
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| 150 | height="31" width="88"></a></p> |
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| 151 | |
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| 152 | <p>Revised |
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| 153 | <!--webbot bot="Timestamp" s-type="EDITED" s-format="%d %B, %Y" startspan -->05 |
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| 154 | December, 2006<!--webbot bot="Timestamp" endspan i-checksum="38516" --></p> |
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| 155 | |
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| 156 | <p><i>Copyright © 2003-2004 <a href= |
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| 157 | "../../people/jens_maurer.htm">Jens Maurer</a></i></p> |
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| 158 | |
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| 159 | <p><i>Distributed under the Boost Software License, Version 1.0. (See |
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| 160 | accompanying file <a href="../../LICENSE_1_0.txt">LICENSE_1_0.txt</a> or |
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| 161 | copy at <a href= |
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| 162 | "http://www.boost.org/LICENSE_1_0.txt">http://www.boost.org/LICENSE_1_0.txt</a>)</i></p> |
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| 163 | </body> |
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| 164 | </html> |
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