122 lines
9.0 KiB
HTML
122 lines
9.0 KiB
HTML
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<title>std::discrete_distribution<IntType>::discrete_distribution</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_numeric_random_discrete_distribution_discrete_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::discrete_distribution<IntType>::</span>discrete_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>‎ | <a href="cpp-numeric-random-discrete_distribution.html">discrete distribution</a></span></div>
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<div><span class="mw-geshi cpp source-cpp">discrete_distribution<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span></span></div>
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<td>(1)</td>
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<td><span class="t-mark-rev t-since-cxx11">(C++11 起)</span></td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1"><</span> <span class="kw1">class</span> InputIt <span class="sy1">></span><br />
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discrete_distribution<span class="br0">(</span> InputIt first, InputIt last <span class="br0">)</span><span class="sy4">;</span></span></div>
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<td>(2)</td>
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<td><span class="t-mark-rev t-since-cxx11">(C++11 起)</span></td>
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<div><span class="mw-geshi cpp source-cpp">discrete_distribution<span class="br0">(</span> <a href="cpp-utility-initializer_list.html"><span class="kw960">std::<span class="me2">initializer_list</span></span></a><span class="sy1"><</span><span class="kw4">double</span><span class="sy1">></span> weights <span class="br0">)</span><span class="sy4">;</span></span></div>
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<td>(3)</td>
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<td><span class="t-mark-rev t-since-cxx11">(C++11 起)</span></td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1"><</span> <span class="kw1">class</span> UnaryOperation <span class="sy1">></span><br /></span>
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<p>discrete_distribution<span class="br0">(</span> <a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> count, <span class="kw4">double</span> xmin, <span class="kw4">double</span> xmax,<br /></p>
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UnaryOperation unary_op <span class="br0">)</span><span class="sy4">;</span></div>
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<td>(4)</td>
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<td><span class="t-mark-rev t-since-cxx11">(C++11 起)</span></td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">explicit</span> discrete_distribution<span class="br0">(</span> <span class="kw4">const</span> param_type<span class="sy3">&</span> params <span class="br0">)</span><span class="sy4">;</span></span></div>
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<td>(5)</td>
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<td><span class="t-mark-rev t-since-cxx11">(C++11 起)</span></td>
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<td></td>
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<td></td>
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<td></td>
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<p>构造新的分布对象。</p>
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<p>1) 默认分布函数。构造拥有单个权重 <span class="texhtml" style="white-space: nowrap;">p={1}</span> 的分布。此分布始终生成 <span class="t-c"><span class="mw-geshi cpp source-cpp">​<span class="nu0">0</span>​</span></span> 。</p>
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<p>2) 构造拥有范围 <code>[first, last)</code> 中权重的分布。若 <span class="t-c"><span class="mw-geshi cpp source-cpp">first <span class="sy1">==</span> last</span></span> ，则效果同默认构造函数。</p>
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<p>3) 构造拥有 <code>weights</code> 中权重的分布。等效地调用 <span class="t-c"><span class="mw-geshi cpp source-cpp">discrete_distribution<span class="br0">(</span>weights.<span class="me1">begin</span><span class="br0">(</span><span class="br0">)</span>, weights.<span class="me1">end</span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span></span></span> 。</p>
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4) 构造拥有以函数 <code>unary_op</code> 生成的 <code>count</code> 个权重的分布。每个权重等于 <span class="texhtml" style="white-space: nowrap;">w<span class="t-su t-su-b"><br />
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i</span> = unary_op(xmin + δ/2 + i · δ)</span> ，其中 <span class="texhtml" style="white-space: nowrap;">δ = <span class="t-mfrac"></span></span>
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<table>
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<td>(xmax − xmin)</td>
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<td>count</td>
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而 <span class="texhtml" style="white-space: nowrap;">i ∈ {0, ..., count−1}</span> 。 <code>xmin</code> 与 <code>xmax</code> 必须使得 <span class="texhtml" style="white-space: nowrap;">δ > 0</span> 。若 <span class="t-c"><span class="mw-geshi cpp source-cpp">count <span class="sy1">==</span> <span class="nu0">0</span></span></span> ，则效果同默认构造函数。
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<p>5) 以 <code>params</code> 为分布参数构造分布。</p>
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<h3><span class="mw-headline" id=".E5.8F.82.E6.95.B0">参数</span></h3>
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<table class="t-par-begin">
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<td>first, last</td>
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<td>-</td>
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<td>定义用作权重的数的元素范围。 <code>InputIterator</code> 所指的元素类型必须可转换为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">double</span></span></span></td>
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</tr>
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<td>weights</td>
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<td>-</td>
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<td>含权重的 initializer_list</td>
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</tr>
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<td>unary_op</td>
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<td>-</td>
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<td>将要应用的一元算符函数。<br />
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函数签名应等价于如下者：
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<p><span class="t-cc"><span class="mw-geshi cpp source-cpp"> Ret fun<span class="br0">(</span><span class="kw4">const</span> Type <span class="sy3">&</span>a<span class="br0">)</span><span class="sy4">;</span></span></span></p>
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<p>签名不必有 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">const</span> <span class="sy3">&</span></span></span> 。<br />
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类型 <span class="t-c"><span class="mw-geshi cpp source-cpp">Type</span></span> 必须使得 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">double</span></span></span> 类型对象能在解引用后隐式转换到 <span class="t-c"><span class="mw-geshi cpp source-cpp">Type</span></span> 。 类型 <span class="t-c"><span class="mw-geshi cpp source-cpp">Ret</span></span> 必须使得 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">double</span></span></span> 类型对象能被解引用并能被赋 <span class="t-c"><span class="mw-geshi cpp source-cpp">Ret</span></span> 类型值。 ​</p>
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</td>
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<td>params</td>
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<td>-</td>
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<td>分布参数集</td>
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<td colspan="3">类型要求</td>
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<td colspan="3">-
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<div class="spacer"></div>
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<code>InputIt</code> 必须满足<a href="cpp-named_req-InputIterator.html"><span style="font-style:italic">老式输入迭代器</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(LegacyInputIterator)</span></a> 的要求。</td>
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<div class="visualClear"></div>
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