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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"><</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">></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"><</span><span class="identifier">overflow_error</span><span class="special"><</span><span class="identifier">errno_on_error</span><span class="special">></span> <span class="special">></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"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></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"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></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"><</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">></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"><</span><span class="identifier">assert_undefined</span><span class="special"><</span><span class="keyword">false</span><span class="special">></span> <span class="special">></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">&</span> <span class="identifier">e</span><span class="special">)</span> | |
124 | <span class="special">{</span> | |
125 | <span class="identifier">cout</span> <span class="special"><<</span> <span class="identifier">e</span><span class="special">.</span><span class="identifier">what</span><span class="special">()</span> <span class="special"><<</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"><</span><span class="keyword">double</span><span class="special">,</span> <span class="identifier">my_policy</span><span class="special">></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"><</span><span class="keyword">double</span><span class="special">,</span> <span class="identifier">my_policy</span><span class="special">></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 © 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 Råde, 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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