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8 | <title>Boost Random Number Library Variate Generator</title> |
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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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