212 lines
13 KiB
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212 lines
13 KiB
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<title>std::bernoulli_distribution</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_numeric_random_bernoulli_distribution skin-cppreference2 action-view cpp-navbar">
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::</span>bernoulli_distribution</h1>
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<div id="contentSub"><span class="subpages">< <a href="cpp.html">cpp</a>‎ | <a href="cpp-numeric.html">numeric</a>‎ | <a href="cpp-numeric-random.html">random</a></span></div>
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<div>定义于头文件 <code><a href="cpp-header-random.html"><random></a></code></div>
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<td></td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">class</span> bernoulli_distribution<span class="sy4">;</span></span></div>
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<td><span class="t-mark-rev t-since-cxx11">(C++11 起)</span></td>
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<p>根据离散概率函数产生随机布尔值。 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">true</span></span></span> 的概率为</p>
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<dl>
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<dd><span class="texhtml" style="white-space: nowrap;">P(b|p) =</span><span class="t-mparen"><span style="font-size: 1em">⎧<br />
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⎨<br />
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⎩</span><span style="text-align:right"><span class="texhtml" style="white-space: nowrap;">p</span> if <span class="t-c"><span class="mw-geshi cpp source-cpp">b <span class="sy1">==</span> <span class="kw2">true</span> </span></span><br />
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<span class="texhtml" style="white-space: nowrap;">1 − p</span> if <span class="t-c"><span class="mw-geshi cpp source-cpp">b <span class="sy1">==</span> <span class="kw2">false</span></span></span></span><span style="font-size: 1em"></span></span></dd>
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<p><code>std::bernoulli_distribution</code> 满足<a href="cpp-named_req-RandomNumberDistribution.html"><span style="font-style:italic">随机数分布</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(RandomNumberDistribution)</span></a> 。</p>
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<h3><span class="mw-headline" id=".E6.88.90.E5.91.98.E7.B1.BB.E5.9E.8B">成员类型</span></h3>
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<td>成员类型</td>
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<td>定义</td>
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<td><code>result_type</code></td>
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<td><span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">bool</span></span></span></td>
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<td><code>param_type</code><span class="t-mark-rev t-since-cxx11">(C++11)</span></td>
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<td>参数集的类型，见<a href="cpp-named_req-RandomNumberDistribution.html"><span style="font-style:italic">随机数分布</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(RandomNumberDistribution)</span></a> 。</td>
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<h3><span class="mw-headline" id=".E6.88.90.E5.91.98.E5.87.BD.E6.95.B0">成员函数</span></h3>
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<div class="t-dsc-member-div t-dsc-member-nobold-div">
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<div><a href="cpp-numeric-random-bernoulli_distribution-bernoulli_distribution.html"><span class="t-lines"><span>(构造函数)</span></span></a></div>
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<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div>
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<td>构造新分布<br />
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<span class="t-mark">(公开成员函数)</span></td>
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<div><a href="cpp-numeric-random-bernoulli_distribution-reset.html"><span class="t-lines"><span>reset</span></span></a></div>
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<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div>
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</div>
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</td>
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<td>重置分布的内部状态<br />
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<span class="t-mark">(公开成员函数)</span></td>
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<td colspan="2">
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<h5><span class="mw-headline" id=".E7.94.9F.E6.88.90">生成</span></h5>
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<div><a href="cpp-numeric-random-bernoulli_distribution-operator().html"><span class="t-lines"><span>operator()</span></span></a></div>
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<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div>
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</div>
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</td>
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<td>生成分布中的下个随机数<br />
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<span class="t-mark">(公开成员函数)</span></td>
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<h5><span class="mw-headline" id=".E7.89.B9.E5.BE.81">特征</span></h5>
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<div><a href="cpp-numeric-random-bernoulli_distribution-p.html"><span class="t-lines"><span>p</span></span></a></div>
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<td>返回 <i>p</i> 分布参数（生成 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">true</span></span></span> 的概率）<br />
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<span class="t-mark">(公开成员函数)</span></td>
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<div><a href="cpp-numeric-random-bernoulli_distribution-param.html"><span class="t-lines"><span>param</span></span></a></div>
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<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div>
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</div>
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<td>获取或设置随机参数对象<br />
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<span class="t-mark">(公开成员函数)</span></td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-numeric-random-bernoulli_distribution-min.html"><span class="t-lines"><span>min</span></span></a></div>
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<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div>
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<td>返回最小的潜在生成值<br />
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<span class="t-mark">(公开成员函数)</span></td>
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<div><a href="cpp-numeric-random-bernoulli_distribution-max.html"><span class="t-lines"><span>max</span></span></a></div>
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<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div>
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<td>返回最大的潜在生成值<br />
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<span class="t-mark">(公开成员函数)</span></td>
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<h3><span class="mw-headline" id=".E9.9D.9E.E6.88.90.E5.91.98.E5.87.BD.E6.95.B0">非成员函数</span></h3>
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<div><a href="cpp-numeric-random-bernoulli_distribution-operator_cmp.html"><span class="t-lines"><span>operator==</span><span>operator!=</span></span></a></div>
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<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span><span><span class="t-mark-rev t-since-cxx11">(C++11)</span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span></span></div>
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</div>
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</td>
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<td>比较两个分布对象<br />
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<span class="t-mark">(函数)</span></td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-numeric-random-bernoulli_distribution-operator_ltltgtgt.html"><span class="t-lines"><span>operator<<</span><span>operator>></span></span></a></div>
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<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div>
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</div>
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</td>
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<td>执行伪随机数分布的流输入和输出<br />
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<span class="t-mark">(函数模板)</span></td>
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<h3><span class="mw-headline" id=".E7.A4.BA.E4.BE.8B">示例</span></h3>
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<div class="t-example">
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<div class="t-example-live-link"></div>
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<div dir="ltr" class="mw-geshi" style="text-align: left;">
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<div class="cpp source-cpp">
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<pre class="de1"><span class="co2">#include <iostream></span>
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<span class="co2">#include <iomanip></span>
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<span class="co2">#include <string></span>
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<span class="co2">#include <map></span>
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<span class="co2">#include <random></span>
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<span class="kw4">int</span> main<span class="br0">(</span><span class="br0">)</span>
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<span class="br0">{</span>
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<a href="cpp-numeric-random-random_device.html"><span class="kw1486">std::<span class="me2">random_device</span></span></a> rd<span class="sy4">;</span>
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<a href="cpp-numeric-random-mersenne_twister_engine.html"><span class="kw1489">std::<span class="me2">mt19937</span></span></a> gen<span class="br0">(</span>rd<span class="br0">(</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="co1">// 1/4 时间给出 "true"</span>
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<span class="co1">// 3/4 时间给出 "false"</span>
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std<span class="sy4">::</span><span class="me2">bernoulli_distribution</span> d<span class="br0">(</span><span class="nu16">0.25</span><span class="br0">)</span><span class="sy4">;</span>
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<a href="cpp-container-map.html"><span class="kw1281">std::<span class="me2">map</span></span></a><span class="sy1"><</span><span class="kw4">bool</span>, <span class="kw4">int</span><span class="sy1">></span> hist<span class="sy4">;</span>
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<span class="kw1">for</span><span class="br0">(</span><span class="kw4">int</span> n<span class="sy1">=</span><span class="nu0">0</span><span class="sy4">;</span> n<span class="sy1"><</span><span class="nu0">10000</span><span class="sy4">;</span> <span class="sy2">++</span>n<span class="br0">)</span> <span class="br0">{</span>
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<span class="sy2">++</span>hist<span class="br0">[</span>d<span class="br0">(</span>gen<span class="br0">)</span><span class="br0">]</span><span class="sy4">;</span>
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<span class="br0">}</span>
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<span class="kw1">for</span><span class="br0">(</span><span class="kw4">auto</span> p <span class="sy4">:</span> hist<span class="br0">)</span> <span class="br0">{</span>
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<a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <a href="cpp-io-manip-boolalpha.html"><span class="kw1763">std::<span class="me2">boolalpha</span></span></a> <span class="sy1"><<</span> <a href="cpp-io-manip-setw.html"><span class="kw1796">std::<span class="me2">setw</span></span></a><span class="br0">(</span><span class="nu0">5</span><span class="br0">)</span> <span class="sy1"><<</span> p.<span class="me1">first</span>
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<span class="sy1"><<</span> <span class="st0">' '</span> <span class="sy1"><<</span> <a href="cpp-string-basic_string.html"><span class="kw1230">std::<span class="me2">string</span></span></a><span class="br0">(</span>p.<span class="me1">second</span><span class="sy2">/</span><span class="nu0">500</span>, <span class="st0">'*'</span><span class="br0">)</span> <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
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<span class="br0">}</span>
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<span class="br0">}</span></pre></div>
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</div>
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<p>可能的输出：</p>
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<div dir="ltr" class="mw-geshi" style="text-align: left;">
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<div class="text source-text">
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<pre class="de1">false ***************
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true ****</pre></div>
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<h3><span class="mw-headline" id=".E5.A4.96.E9.83.A8.E9.93.BE.E6.8E.A5">外部链接</span></h3>
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<p><a rel="nofollow" class="external text" href="http://mathworld.wolfram.com/BernoulliDistribution.html">Weisstein, Eric W. “伯努利分布。”</a>来自 MathWorld--A Wolfram Web Resource 。</p>
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