1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 4<title>Conceptual Archetypes for Reals and Distributions</title> 5<link rel="stylesheet" href="../math.css" type="text/css"> 6<meta name="generator" content="DocBook XSL Stylesheets V1.79.1"> 7<link rel="home" href="../index.html" title="Math Toolkit 2.12.0"> 8<link rel="up" href="../using_udt.html" title="Chapter 20. Use with User-Defined Floating-Point Types - Boost.Multiprecision and others"> 9<link rel="prev" href="dist_concept.html" title="Conceptual Requirements for Distribution Types"> 10<link rel="next" href="../policy.html" title="Chapter 21. Policies: Controlling Precision, Error Handling etc"> 11</head> 12<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> 13<table cellpadding="2" width="100%"><tr> 14<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../boost.png"></td> 15<td align="center"><a href="../../../../../index.html">Home</a></td> 16<td align="center"><a href="../../../../../libs/libraries.htm">Libraries</a></td> 17<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td> 18<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td> 19<td align="center"><a href="../../../../../more/index.htm">More</a></td> 20</tr></table> 21<hr> 22<div class="spirit-nav"> 23<a accesskey="p" href="dist_concept.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../using_udt.html"><img src="../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="../policy.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a> 24</div> 25<div class="section"> 26<div class="titlepage"><div><div><h2 class="title" style="clear: both"> 27<a name="math_toolkit.archetypes"></a><a class="link" href="archetypes.html" title="Conceptual Archetypes for Reals and Distributions">Conceptual Archetypes for Reals 28 and Distributions</a> 29</h2></div></div></div> 30<p> 31 There are a few concept archetypes available: 32 </p> 33<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> 34<li class="listitem"> 35 Real concept for floating-point types. 36 </li> 37<li class="listitem"> 38 Distribution concept for statistical distributions. 39 </li> 40</ul></div> 41<h6> 42<a name="math_toolkit.archetypes.h0"></a> 43 <span class="phrase"><a name="math_toolkit.archetypes.real_concept"></a></span><a class="link" href="archetypes.html#math_toolkit.archetypes.real_concept">Real 44 concept</a> 45 </h6> 46<p> 47 <code class="computeroutput"><span class="identifier">std_real_concept</span></code> is an archetype 48 for theReal types, including the built-in float, double, long double. 49 </p> 50<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">concepts</span><span class="special">/</span><span class="identifier">std_real_concept</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span></pre> 51<pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">{</span> 52<span class="keyword">namespace</span> <span class="identifier">math</span><span class="special">{</span> 53<span class="keyword">namespace</span> <span class="identifier">concepts</span> 54<span class="special">{</span> 55 <span class="keyword">class</span> <span class="identifier">std_real_concept</span><span class="special">;</span> 56<span class="special">}</span> 57<span class="special">}}</span> <span class="comment">// namespaces</span> 58</pre> 59<p> 60 The main purpose in providing this type is to verify that standard library 61 functions are found via a using declaration - bringing those functions into 62 the current scope - and not just because they happen to be in global scope. 63 </p> 64<p> 65 In order to ensure that a call to say <code class="computeroutput"><span class="identifier">pow</span></code> 66 can be found either via argument dependent lookup, or failing that then in 67 the std namespace: all calls to standard library functions are unqualified, 68 with the std:: versions found via a <code class="computeroutput"><span class="keyword">using</span></code> 69 declaration to make them visible in the current scope. Unfortunately it's all 70 to easy to forget the <code class="computeroutput"><span class="keyword">using</span></code> declaration, 71 and call the double version of the function that happens to be in the global 72 scope by mistake. 73 </p> 74<p> 75 For example if the code calls ::pow rather than std::pow, the code will cleanly 76 compile, but truncation of long doubles to double will cause a significant 77 loss of precision. In contrast a template instantiated with std_real_concept 78 will <span class="bold"><strong>only</strong></span> compile if the all the standard 79 library functions used have been brought into the current scope with a using 80 declaration. 81 </p> 82<h3> 83<a name="math_toolkit.archetypes.h1"></a> 84 <span class="phrase"><a name="math_toolkit.archetypes.testing_the_real_concept"></a></span><a class="link" href="archetypes.html#math_toolkit.archetypes.testing_the_real_concept">Testing 85 the real concept</a> 86 </h3> 87<p> 88 There is a test program <a href="../../../test/std_real_concept_check.cpp" target="_top">libs/math/test/std_real_concept_check.cpp</a> 89 that instantiates every template in this library with type <code class="computeroutput"><span class="identifier">std_real_concept</span></code> 90 to verify its usage of standard library functions. 91 </p> 92<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">concepts</span><span class="special">/</span><span class="identifier">real_concept</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span></pre> 93<pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">{</span> 94<span class="keyword">namespace</span> <span class="identifier">math</span><span class="special">{</span> 95<span class="keyword">namespace</span> <span class="identifier">concepts</span><span class="special">{</span> 96 97<span class="keyword">class</span> <span class="identifier">real_concept</span><span class="special">;</span> 98 99<span class="special">}}}</span> <span class="comment">// namespaces</span> 100</pre> 101<p> 102 <code class="computeroutput"><span class="identifier">real_concept</span></code> is an archetype 103 for <a class="link" href="real_concepts.html" title="Conceptual Requirements for Real Number Types">user defined real types</a>, 104 it declares its standard library functions in its own namespace: these will 105 only be found if they are called unqualified allowing argument dependent lookup 106 to locate them. In addition this type is useable at runtime: this allows code 107 that would not otherwise be exercised by the built-in floating point types 108 to be tested. There is no std::numeric_limits<> support for this type, 109 since numeric_limits is not a conceptual requirement for <a class="link" href="real_concepts.html" title="Conceptual Requirements for Real Number Types">RealType</a>s. 110 </p> 111<p> 112 NTL RR is an example of a type meeting the requirements that this type models, 113 but note that use of a thin wrapper class is required: refer to <a class="link" href="high_precision/use_ntl.html" title="Using NTL Library">"Using 114 With NTL - a High-Precision Floating-Point Library"</a>. 115 </p> 116<p> 117 There is no specific test case for type <code class="computeroutput"><span class="identifier">real_concept</span></code>, 118 instead, since this type is usable at runtime, each individual test case as 119 well as testing <code class="computeroutput"><span class="keyword">float</span></code>, <code class="computeroutput"><span class="keyword">double</span></code> and <code class="computeroutput"><span class="keyword">long</span> 120 <span class="keyword">double</span></code>, also tests <code class="computeroutput"><span class="identifier">real_concept</span></code>. 121 </p> 122<h3> 123<a name="math_toolkit.archetypes.h2"></a> 124 <span class="phrase"><a name="math_toolkit.archetypes.distribution_concept"></a></span><a class="link" href="archetypes.html#math_toolkit.archetypes.distribution_concept">Distribution 125 Concept</a> 126 </h3> 127<p> 128 Distribution Concept models statistical distributions. 129 </p> 130<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">concepts</span><span class="special">/</span><span class="identifier">distribution</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span></pre> 131<pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">{</span> 132<span class="keyword">namespace</span> <span class="identifier">math</span><span class="special">{</span> 133<span class="keyword">namespace</span> <span class="identifier">concepts</span> 134<span class="special">{</span> 135 <span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">RealType</span><span class="special">></span> 136 <span class="keyword">class</span> <span class="identifier">distribution_archetype</span><span class="special">;</span> 137 138 <span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">Distribution</span><span class="special">></span> 139 <span class="keyword">struct</span> <span class="identifier">DistributionConcept</span><span class="special">;</span> 140 141<span class="special">}}}</span> <span class="comment">// namespaces</span> 142</pre> 143<p> 144 The class template <code class="computeroutput"><span class="identifier">distribution_archetype</span></code> 145 is a model of the <a class="link" href="dist_concept.html" title="Conceptual Requirements for Distribution Types">Distribution concept</a>. 146 </p> 147<p> 148 The class template <code class="computeroutput"><span class="identifier">DistributionConcept</span></code> 149 is a <a href="../../../../../libs/concept_check/index.html" target="_top">concept checking 150 class</a> for distribution types. 151 </p> 152<h3> 153<a name="math_toolkit.archetypes.h3"></a> 154 <span class="phrase"><a name="math_toolkit.archetypes.testing_the_distribution_concept"></a></span><a class="link" href="archetypes.html#math_toolkit.archetypes.testing_the_distribution_concept">Testing 155 the distribution concept</a> 156 </h3> 157<p> 158 The test program <a href="../../../test/compile_test/distribution_concept_check.cpp" target="_top">distribution_concept_check.cpp</a> 159 is responsible for using <code class="computeroutput"><span class="identifier">DistributionConcept</span></code> 160 to verify that all the distributions in this library conform to the <a class="link" href="dist_concept.html" title="Conceptual Requirements for Distribution Types">Distribution 161 concept</a>. 162 </p> 163<p> 164 The class template <code class="computeroutput"><span class="identifier">DistributionConcept</span></code> 165 verifies the existence (but not proper function) of the non-member accessors 166 required by the <a class="link" href="dist_concept.html" title="Conceptual Requirements for Distribution Types">Distribution concept</a>. 167 These are checked by calls like 168 </p> 169<pre class="programlisting"><span class="identifier">v</span> <span class="special">=</span> <span class="identifier">pdf</span><span class="special">(</span><span class="identifier">dist</span><span class="special">,</span> <span class="identifier">x</span><span class="special">);</span> <span class="comment">// (Result v is ignored).</span> 170</pre> 171<p> 172 And in addition, those that accept two arguments do the right thing when the 173 arguments are of different types (the result type is always the same as the 174 distribution's value_type). (This is implemented by some additional forwarding-functions 175 in derived_accessors.hpp, so that there is no need for any code changes. Likewise 176 boilerplate versions of the hazard/chf/coefficient_of_variation functions are 177 implemented in there too.) 178 </p> 179</div> 180<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 181<td align="left"></td> 182<td align="right"><div class="copyright-footer">Copyright © 2006-2019 Nikhar 183 Agrawal, Anton Bikineev, Paul A. Bristow, Marco Guazzone, Christopher Kormanyos, 184 Hubert Holin, Bruno Lalande, John Maddock, Jeremy Murphy, Matthew Pulver, Johan 185 Råde, Gautam Sewani, Benjamin Sobotta, Nicholas Thompson, Thijs van den Berg, 186 Daryle Walker and Xiaogang Zhang<p> 187 Distributed under the Boost Software License, Version 1.0. (See accompanying 188 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>) 189 </p> 190</div></td> 191</tr></table> 192<hr> 193<div class="spirit-nav"> 194<a accesskey="p" href="dist_concept.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../using_udt.html"><img src="../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="../policy.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a> 195</div> 196</body> 197</html> 198
