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    25. 

  25. <div class="section">
    26. 

  26. <div class="titlepage"><div><div><h3 class="title">
    27. 

  27. <a name="math_toolkit.pol_ref.namespace_pol"></a><a class="link" href="namespace_pol.html" title="Setting Polices at Namespace Scope">Setting Polices at
    28. 

  28.       Namespace Scope</a>
    29. 

  29. </h3></div></div></div>
    30. 

  30. <p>
    31. 

  31.         Sometimes what you really want to do is bring all the special functions,
    32. 

  32.         or all the distributions into a specific namespace-scope, along with a specific
    33. 

  33.         policy to use with them. There are two macros defined to assist with that:
    34. 

  34.       </p>
    35. 

  35. <pre class="programlisting"><span class="identifier">BOOST_MATH_DECLARE_SPECIAL_FUNCTIONS</span><span class="special">(</span><span class="identifier">Policy</span><span class="special">)</span>
    36. 

  36. </pre>
    37. 

  37. <p>
    38. 

  38.         and:
    39. 

  39.       </p>
    40. 

  40. <pre class="programlisting"><span class="identifier">BOOST_MATH_DECLARE_DISTRIBUTIONS</span><span class="special">(</span><span class="identifier">Type</span><span class="special">,</span> <span class="identifier">Policy</span><span class="special">)</span>
    41. 

  41. </pre>
    42. 

  42. <p>
    43. 

  43.         You can use either of these macros after including any special function or
    44. 

  44.         distribution header. For example:
    45. 

  45.       </p>
    46. 

  46. <pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">math</span><span class="special">/</span><span class="identifier">special_functions</span><span class="special">/</span><span class="identifier">gamma</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
    47. 

  47. <span class="comment">//using boost::math::tgamma;</span>
    48. 

  48. <span class="comment">// Need not declare using boost::math::tgamma here,</span>
    49. 

  49. <span class="comment">// because will define tgamma in myspace using macro below.</span>
    50. 

  50. 

  51. <span class="keyword">namespace</span> <span class="identifier">myspace</span>
    52. 

  52. <span class="special">{</span>
    53. 

  53.   <span class="keyword">using</span> <span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">math</span><span class="special">::</span><span class="identifier">policies</span><span class="special">;</span>
    54. 

  54. 

  55.   <span class="comment">// Define a policy that does not throw on overflow:</span>
    56. 

  56.   <span class="keyword">typedef</span> <span class="identifier">policy</span><span class="special">&lt;</span><span class="identifier">overflow_error</span><span class="special">&lt;</span><span class="identifier">errno_on_error</span><span class="special">&gt;</span> <span class="special">&gt;</span> <span class="identifier">my_policy</span><span class="special">;</span>
    57. 

  57. 

  58.   <span class="comment">// Define the special functions in this scope to use the policy:   </span>
    59. 

  59.   <span class="identifier">BOOST_MATH_DECLARE_SPECIAL_FUNCTIONS</span><span class="special">(</span><span class="identifier">my_policy</span><span class="special">)</span>
    60. 

  60. <span class="special">}</span>
    61. 

  61. 

  62. <span class="comment">// Now we can use myspace::tgamma etc.</span>
    63. 

  63. <span class="comment">// They will automatically use "my_policy":</span>
    64. 

  64. <span class="comment">//</span>
    65. 

  65. <span class="keyword">double</span> <span class="identifier">t</span> <span class="special">=</span> <span class="identifier">myspace</span><span class="special">::</span><span class="identifier">tgamma</span><span class="special">(</span><span class="number">30.0</span><span class="special">);</span> <span class="comment">// Will *not* throw on overflow,</span>
    66. 

  66. <span class="comment">// despite the large value of factorial 30 = 265252859812191058636308480000000</span>
    67. 

  67. <span class="comment">// unlike default policy boost::math::tgamma;</span>
    68. 

  68. </pre>
    69. 

  69. <p>
    70. 

  70.         In this example, using BOOST_MATH_DECLARE_SPECIAL_FUNCTIONS results in a
    71. 

  71.         set of thin inline forwarding functions being defined:
    72. 

  72.       </p>
    73. 

  73. <pre class="programlisting"><span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">&gt;</span>
    74. 

  74. <span class="keyword">inline</span> <span class="identifier">T</span> <span class="identifier">tgamma</span><span class="special">(</span><span class="identifier">T</span> <span class="identifier">a</span><span class="special">){</span> <span class="keyword">return</span> <span class="special">::</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">math</span><span class="special">::</span><span class="identifier">tgamma</span><span class="special">(</span><span class="identifier">a</span><span class="special">,</span> <span class="identifier">mypolicy</span><span class="special">());</span> <span class="special">}</span>
    75. 

  75. 

  76. <span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">&gt;</span>
    77. 

  77. <span class="keyword">inline</span> <span class="identifier">T</span> <span class="identifier">lgamma</span><span class="special">(</span><span class="identifier">T</span> <span class="identifier">a</span><span class="special">)</span> <span class="special">(</span> <span class="keyword">return</span> <span class="special">::</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">math</span><span class="special">::</span><span class="identifier">lgamma</span><span class="special">(</span><span class="identifier">a</span><span class="special">,</span> <span class="identifier">mypolicy</span><span class="special">());</span> <span class="special">}</span>
    78. 

  78. </pre>
    79. 

  79. <p>
    80. 

  80.         and so on. Note that while a forwarding function is defined for all the special
    81. 

  81.         functions, however, unless you include the specific header for the special
    82. 

  82.         function you use (or boost/math/special_functions.hpp to include everything),
    83. 

  83.         you will get linker errors from functions that are forward declared, but
    84. 

  84.         not defined.
    85. 

  85.       </p>
    86. 

  86. <p>
    87. 

  87.         We can do the same thing with the distributions, but this time we need to
    88. 

  88.         specify the floating-point type to use:
    89. 

  89.       </p>
    90. 

  90. <pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">math</span><span class="special">/</span><span class="identifier">distributions</span><span class="special">/</span><span class="identifier">cauchy</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
    91. 

  91. 

  92. <span class="keyword">namespace</span> <span class="identifier">myspace</span>
    93. 

  93. <span class="special">{</span> <span class="comment">// using namespace boost::math::policies; // May be convenient in myspace.</span>
    94. 

  94. 

  95.   <span class="comment">// Define a policy called my_policy to use.</span>
    96. 

  96.   <span class="keyword">using</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">math</span><span class="special">::</span><span class="identifier">policies</span><span class="special">::</span><span class="identifier">policy</span><span class="special">;</span>
    97. 

  97. 

  98. <span class="comment">// In this case we want all the distribution accessor functions to compile,</span>
    99. 

  99. <span class="comment">// even if they are mathematically undefined, so</span>
    100. 

  100. <span class="comment">// make the policy assert_undefined.</span>
    101. 

  101.   <span class="keyword">using</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">math</span><span class="special">::</span><span class="identifier">policies</span><span class="special">::</span><span class="identifier">assert_undefined</span><span class="special">;</span>
    102. 

  102. 

  103. <span class="keyword">typedef</span> <span class="identifier">policy</span><span class="special">&lt;</span><span class="identifier">assert_undefined</span><span class="special">&lt;</span><span class="keyword">false</span><span class="special">&gt;</span> <span class="special">&gt;</span> <span class="identifier">my_policy</span><span class="special">;</span>
    104. 

  104. 

  105. <span class="comment">// Finally apply this policy to type double.</span>
    106. 

  106. <span class="identifier">BOOST_MATH_DECLARE_DISTRIBUTIONS</span><span class="special">(</span><span class="keyword">double</span><span class="special">,</span> <span class="identifier">my_policy</span><span class="special">)</span>
    107. 

  107. <span class="special">}</span> <span class="comment">// namespace myspace</span>
    108. 

  108. 

  109. <span class="comment">// Now we can use myspace::cauchy etc, which will use policy</span>
    110. 

  110. <span class="comment">// myspace::mypolicy:</span>
    111. 

  111. <span class="comment">//</span>
    112. 

  112. <span class="comment">// This compiles but throws a domain error exception at runtime.</span>
    113. 

  113. <span class="comment">// Caution! If you omit the try'n'catch blocks, </span>
    114. 

  114. <span class="comment">// it will just silently terminate, giving no clues as to why! </span>
    115. 

  115. <span class="comment">// So try'n'catch blocks are very strongly recommended.</span>
    116. 

  116. 

  117. <span class="keyword">void</span> <span class="identifier">test_cauchy</span><span class="special">()</span>
    118. 

  118. <span class="special">{</span>
    119. 

  119.    <span class="keyword">try</span>
    120. 

  120.    <span class="special">{</span>
    121. 

  121.       <span class="keyword">double</span> <span class="identifier">d</span> <span class="special">=</span> <span class="identifier">mean</span><span class="special">(</span><span class="identifier">myspace</span><span class="special">::</span><span class="identifier">cauchy</span><span class="special">());</span>  <span class="comment">// Cauchy does not have a mean!</span>
    122. 

  122.       <span class="special">(</span><span class="keyword">void</span><span class="special">)</span> <span class="identifier">d</span><span class="special">;</span>
    123. 

  123.    <span class="special">}</span>
    124. 

  124.    <span class="keyword">catch</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">domain_error</span><span class="special">&amp;</span> <span class="identifier">e</span><span class="special">)</span>
    125. 

  125.    <span class="special">{</span>
    126. 

  126.       <span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="identifier">e</span><span class="special">.</span><span class="identifier">what</span><span class="special">()</span> <span class="special">&lt;&lt;</span> <span class="identifier">endl</span><span class="special">;</span>
    127. 

  127.    <span class="special">}</span>
    128. 

  128. <span class="special">}</span>
    129. 

  129. </pre>
    130. 

  130. <p>
    131. 

  131.         In this example the result of BOOST_MATH_DECLARE_DISTRIBUTIONS is to declare
    132. 

  132.         a typedef for each distribution like this:
    133. 

  133.       </p>
    134. 

  134. <pre class="programlisting"><span class="keyword">typedef</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">math</span><span class="special">::</span><span class="identifier">cauchy_distribution</span><span class="special">&lt;</span><span class="keyword">double</span><span class="special">,</span> <span class="identifier">my_policy</span><span class="special">&gt;</span> <span class="identifier">cauchy</span><span class="special">;</span>
    135. 

  135. <span class="identifier">tyepdef</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">math</span><span class="special">::</span><span class="identifier">gamma_distribution</span><span class="special">&lt;</span><span class="keyword">double</span><span class="special">,</span> <span class="identifier">my_policy</span><span class="special">&gt;</span> <span class="identifier">gamma</span><span class="special">;</span>
    136. 

  136. </pre>
    137. 

  137. <p>
    138. 

  138.         and so on. The name given to each typedef is the name of the distribution
    139. 

  139.         with the "_distribution" suffix removed.
    140. 

  140.       </p>
    141. 

  141. </div>
    142. 

  142. <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
    143. 

  143. <td align="left"></td>
    144. 

  144. <td align="right"><div class="copyright-footer">Copyright &#169; 2006-2019 Nikhar
    145. 

  145.       Agrawal, Anton Bikineev, Paul A. Bristow, Marco Guazzone, Christopher Kormanyos,
    146. 

  146.       Hubert Holin, Bruno Lalande, John Maddock, Jeremy Murphy, Matthew Pulver, Johan
    147. 

  147.       R&#229;de, Gautam Sewani, Benjamin Sobotta, Nicholas Thompson, Thijs van den Berg,
    148. 

  148.       Daryle Walker and Xiaogang Zhang<p>
    149. 

  149.         Distributed under the Boost Software License, Version 1.0. (See accompanying
    150. 

  150.         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>)
    151. 

  151.       </p>
    152. 

  152. </div></td>
    153. 

  153. </tr></table>
    154. 

  154. <hr>
    155. 

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    157. 

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    158. 

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