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  26 <div class="titlepage"><div><div><h3 class="title">
  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       Namespace Scope</a>
  29 </h3></div></div></div>
  30 <p>
  31         Sometimes what you really want to do is bring all the special functions,
  32         or all the distributions into a specific namespace-scope, along with a specific
  33         policy to use with them. There are two macros defined to assist with that:
  34       </p>
  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 </pre>
  37 <p>
  38         and:
  39       </p>
  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 </pre>
  42 <p>
  43         You can use either of these macros after including any special function or
  44         distribution header. For example:
  45       </p>
  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 <span class="comment">//using boost::math::tgamma;</span>
  48 <span class="comment">// Need not declare using boost::math::tgamma here,</span>
  49 <span class="comment">// because will define tgamma in myspace using macro below.</span>
  50
  51 <span class="keyword">namespace</span> <span class="identifier">myspace</span>
  52 <span class="special">{</span>
  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
  55   <span class="comment">// Define a policy that does not throw on overflow:</span>
  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
  58   <span class="comment">// Define the special functions in this scope to use the policy:   </span>
  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 <span class="special">}</span>
  61
  62 <span class="comment">// Now we can use myspace::tgamma etc.</span>
  63 <span class="comment">// They will automatically use "my_policy":</span>
  64 <span class="comment">//</span>
  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 <span class="comment">// despite the large value of factorial 30 = 265252859812191058636308480000000</span>
  67 <span class="comment">// unlike default policy boost::math::tgamma;</span>
  68 </pre>
  69 <p>
  70         In this example, using BOOST_MATH_DECLARE_SPECIAL_FUNCTIONS results in a
  71         set of thin inline forwarding functions being defined:
  72       </p>
  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 <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
  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 <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 </pre>
  79 <p>
  80         and so on. Note that while a forwarding function is defined for all the special
  81         functions, however, unless you include the specific header for the special
  82         function you use (or boost/math/special_functions.hpp to include everything),
  83         you will get linker errors from functions that are forward declared, but
  84         not defined.
  85       </p>
  86 <p>
  87         We can do the same thing with the distributions, but this time we need to
  88         specify the floating-point type to use:
  89       </p>
  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
  92 <span class="keyword">namespace</span> <span class="identifier">myspace</span>
  93 <span class="special">{</span> <span class="comment">// using namespace boost::math::policies; // May be convenient in myspace.</span>
  94
  95   <span class="comment">// Define a policy called my_policy to use.</span>
  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
  98 <span class="comment">// In this case we want all the distribution accessor functions to compile,</span>
  99 <span class="comment">// even if they are mathematically undefined, so</span>
 100 <span class="comment">// make the policy assert_undefined.</span>
 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
 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
 105 <span class="comment">// Finally apply this policy to type double.</span>
 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 <span class="special">}</span> <span class="comment">// namespace myspace</span>
 108
 109 <span class="comment">// Now we can use myspace::cauchy etc, which will use policy</span>
 110 <span class="comment">// myspace::mypolicy:</span>
 111 <span class="comment">//</span>
 112 <span class="comment">// This compiles but throws a domain error exception at runtime.</span>
 113 <span class="comment">// Caution! If you omit the try'n'catch blocks, </span>
 114 <span class="comment">// it will just silently terminate, giving no clues as to why! </span>
 115 <span class="comment">// So try'n'catch blocks are very strongly recommended.</span>
 116
 117 <span class="keyword">void</span> <span class="identifier">test_cauchy</span><span class="special">()</span>
 118 <span class="special">{</span>
 119    <span class="keyword">try</span>
 120    <span class="special">{</span>
 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    <span class="special">}</span>
 123    <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>
 124    <span class="special">{</span>
 125       <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>
 126    <span class="special">}</span>
 127 <span class="special">}</span>
 128 </pre>
 129 <p>
 130         In this example the result of BOOST_MATH_DECLARE_DISTRIBUTIONS is to declare
 131         a typedef for each distribution like this:
 132       </p>
 133 <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>
 134 <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>
 135 </pre>
 136 <p>
 137         and so on. The name given to each typedef is the name of the distribution
 138         with the "_distribution" suffix removed.
 139       </p>
 140 </div>
 141 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
 142 <td align="left"></td>
 143 <td align="right"><div class="copyright-footer">Copyright &#169; 2006-2010, 2012-2014 Nikhar Agrawal,
 144       Anton Bikineev, Paul A. Bristow, Marco Guazzone, Christopher Kormanyos, Hubert
 145       Holin, Bruno Lalande, John Maddock, Jeremy Murphy, Johan R&#229;de, Gautam Sewani,
 146       Benjamin Sobotta, Thijs van den Berg, Daryle Walker and Xiaogang Zhang<p>
 147         Distributed under the Boost Software License, Version 1.0. (See accompanying
 148         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>)
 149       </p>
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