126 lines
9.2 KiB
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126 lines
9.2 KiB
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<title>std::mersenne_twister_engine<UIntType,w,n,m,r,a,u,d,s,b,t,c,l,f>::mersenne_twister_engine</title>
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::mersenne_twister_engine<UIntType,w,n,m,r,a,u,d,s,b,t,c,l,f>::</span>mersenne_twister_engine</h1>
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<div id="bodyContent">
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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-mersenne_twister_engine.html">mersenne twister engine</a></span></div>
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<div id="mw-content-text" lang="zh" dir="ltr" class="mw-content-ltr" xml:lang="zh">
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<div class="t-page-template" style="">
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<p></p>
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</div>
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<table class="t-dcl-begin">
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<div><span class="mw-geshi cpp source-cpp">mersenne_twister_engine<span class="br0">(</span><span class="br0">)</span> <span class="sy4">:</span> mersenne_twister_engine<span class="br0">(</span>default_seed<span class="br0">)</span> <span class="br0">{</span><span class="br0">}</span></span></div>
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</td>
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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">explicit</span> mersenne_twister_engine<span class="br0">(</span> result_type value <span class="br0">)</span><span class="sy4">;</span></span></div>
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</td>
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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"><span class="kw1">template</span><span class="sy1"><</span> <span class="kw1">class</span> Sseq <span class="sy1">></span><br />
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<span class="kw1">explicit</span> mersenne_twister_engine<span class="br0">(</span> Sseq<span class="sy3">&</span> s <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">mersenne_twister_engine<span class="br0">(</span> <span class="kw4">const</span> mersenne_twister_engine<span class="sy3">&</span> <span class="br0">)</span><span class="sy4">;</span></span></div>
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</td>
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<td>(4)</td>
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<td><span class="t-mark-rev t-since-cxx11">(C++11 起)</span><br />
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<span class="t-mark">(隐式声明)</span></td>
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<tr class="t-dcl-sep">
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<td></td>
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<td></td>
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<td></td>
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</tbody>
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<p>构造伪随机数引擎。</p>
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<div class="t-li1"><span class="t-li">1)</span> 默认构造函数。以 <code>default_seed</code> 播种引擎。</div>
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<div class="t-li1"><span class="t-li">2)</span> 构造引擎并初始化状态（ <code>result_type</code> 类型的 <code>n</code> 个值 <span class="texhtml" style="white-space: nowrap;">X<span class="t-su t-su-b"><br />
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i</span></span> ）如下：用 <span class="texhtml" style="white-space: nowrap;">value mod 2<span class="t-su">w<br /></span></span> 初始化 <span class="texhtml" style="white-space: nowrap;">X<span class="t-su t-su-b"><br />
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0</span></span> ，并递推初始化其余内容，对于 <span class="texhtml" style="white-space: nowrap;">i=1-n,...,-1</span> ，初始化每个 <span class="texhtml" style="white-space: nowrap;">X<span class="t-su t-su-b"><br />
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i</span></span> 为 <span class="texhtml" style="white-space: nowrap;">[f·(X<span class="t-su t-su-b"><br />
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i-1</span>xor(X<span class="t-su t-su-b"><br />
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i-1</span>rshift(w-2)))+i mod n] mod 2<span class="t-su">w<br /></span></span> 。</div>
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<div class="t-li1"><span class="t-li">3)</span> 构造引擎并通过调用 <span class="t-c"><span class="mw-geshi cpp source-cpp">s.<span class="me1">generate</span><span class="br0">(</span>a, a<span class="sy2">+</span>n<span class="sy2">*</span>k<span class="br0">)</span></span></span> 初始化状态，其中 a 是长为 n*k 的数组，而 k 为 ceil(w/32) ，然后，对于每个 <span class="texhtml" style="white-space: nowrap;">i=-n,...,-1</span> ，递推地设置引擎状态的元素 <span class="texhtml" style="white-space: nowrap;">X<span class="t-su t-su-b"><br />
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i</span></span> 为 <span class="texhtml" style="white-space: nowrap;">(Σ<span class="t-su t-su-b">k-1<br />
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j=0</span>a<span class="t-su t-su-b"><br />
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k(i+n)+j}·2<span class="t-su">32j<br /></span></span>) mod 2<span class="t-su">w<br /></span></span> ，最后若 <span class="texhtml" style="white-space: nowrap;">X<span class="t-su t-su-b"><br />
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0</span></span> 的最高 <span class="texhtml" style="white-space: nowrap;">w-r</span> 位为零，且若所有其他 <span class="texhtml" style="white-space: nowrap;">X<span class="t-su t-su-b"><br />
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i</span></span> 均为零，则以 <span class="texhtml" style="white-space: nowrap;">2<span class="t-su">w-1<br /></span></span> 替换 <span class="texhtml" style="white-space: nowrap;">X<span class="t-su t-su-b"><br />
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0</span></span> 。</div>
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<p>注意：初始化要求基于梅森缠绕器的 2002 版本， <a rel="nofollow" class="external text" href="http://www.math.sci.hiroshima-u.ac.jp/~m-mat/MT/MT2002/CODES/mt19937ar.c">mt19937ar.c</a></p>
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<p>仅若 <code>Sseq</code> 符合重载<a href="cpp-named_req-SeedSequence.html"><span style="font-style:italic">种子序列</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(SeedSequence)</span></a> ， <span class="t-v">(3)</span> 才参与重载决议。尤其是若 <code>Sseq</code> 可转换为 <code>result_type</code> ，则从候选函数集中排除该重载。</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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<tr class="t-par">
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<td>value</td>
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<td>-</td>
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<td>用于内部状态初始化的种子值</td>
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</tr>
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<tr class="t-par">
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<td>s</td>
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<td>-</td>
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<td>用于内部状态初始化的种子序列</td>
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</tr>
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</table>
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<h3><span class="mw-headline" id=".E5.A4.8D.E6.9D.82.E5.BA.A6">复杂度</span></h3>
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<p>与 <code>n</code> （状态大小）成线性</p>
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<h3><span class="mw-headline" id=".E7.BC.BA.E9.99.B7.E6.8A.A5.E5.91.8A">缺陷报告</span></h3>
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<p>下列更改行为的缺陷报告追溯地应用于以前出版的 C++ 标准。</p>
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<table class="dsctable" style="font-size:0.8em">
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<tr>
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<th>DR</th>
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<th>应用于</th>
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<th>出版时的行为</th>
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<th>正确行为</th>
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</tr>
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<tr>
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<td><a rel="nofollow" class="external text" href="https://wg21.link/P0935R0">P0935R0</a></td>
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<td>C++11</td>
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<td>默认构造函数曾为 explicit</td>
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<td>使之为隐式</td>
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</tr>
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</table>
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<h3><span class="mw-headline" id=".E5.8F.82.E9.98.85">参阅</span></h3>
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<table class="t-dsc-begin">
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<div class="t-dsc-member-div">
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<div><a href="cpp-numeric-random-mersenne_twister_engine-seed.html"><span class="t-lines"><span>seed</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>设置引擎的当前状态<br />
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<span class="t-mark">(公开成员函数)</span></td>
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</table>
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</div>
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<div class="visualClear"></div>
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