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115 lines
3.6 KiB
HTML
115 lines
3.6 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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<html>
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<head>
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<meta http-equiv="content-type" content="text/html; charset=UTF-8">
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<title>自然对数</title>
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</head>
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<body class="docs"><div id="layout">
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<div id="layout-content"><div id="function.log" class="refentry">
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<div class="refnamediv">
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<h1 class="refname">log</h1>
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<p class="verinfo">(PHP 4, PHP 5, PHP 7)</p><p class="refpurpose"><span class="refname">log</span> — <span class="dc-title">自然对数</span></p>
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</div>
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<div class="refsect1 description" id="refsect1-function.log-description">
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<h3 class="title">说明</h3>
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<div class="methodsynopsis dc-description">
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<span class="methodname"><strong>log</strong></span>
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( <span class="methodparam"><span class="type">float</span> <code class="parameter">$arg</code></span>
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[, <span class="methodparam"><span class="type">float</span> <code class="parameter">$base</code><span class="initializer"> = M_E</span></span>
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] ) : <span class="type">float</span></div>
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<p class="para rdfs-comment">
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如果指定了可选的参数 <code class="parameter">base</code>，<span class="function"><strong>log()</strong></span>
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返回 log<sub class="subscript">base</sub>
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<code class="parameter">arg</code>，否则 <span class="function"><strong>log()</strong></span>
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返回参数 <code class="parameter">arg</code> 的自然对数。
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</p>
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</div>
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<div class="refsect1 parameters" id="refsect1-function.log-parameters">
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<h3 class="title">参数</h3>
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<p class="para">
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<dl>
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<dt>
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<code class="parameter">arg</code></dt>
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<dd>
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<p class="para">
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要计算对数的值
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</p>
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</dd>
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<dt>
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<code class="parameter">base</code></dt>
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<dd>
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<p class="para">
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The optional logarithmic base to use
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(defaults to 'e' and so to the natural logarithm).
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</p>
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</dd>
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</dl>
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</p>
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</div>
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<div class="refsect1 returnvalues" id="refsect1-function.log-returnvalues">
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<h3 class="title">返回值</h3>
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<p class="para">
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返回 log<sub class="subscript">base</sub>
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<code class="parameter">arg</code>，或者它的自然对数。
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</p>
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</div>
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<div class="refsect1 changelog" id="refsect1-function.log-changelog">
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<h3 class="title">更新日志</h3>
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<p class="para">
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<table class="doctable informaltable">
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<thead>
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<tr>
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<th>版本</th>
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<th>说明</th>
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</tr>
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</thead>
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<tbody class="tbody">
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<tr>
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<td>4.3.0</td>
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<td>
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可选参数 <code class="parameter">base</code>可用。
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你可以计算任意以 <em>b</em> 为底 <em>n</em>
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的对数，但其实使用的是数学等式：log<sub class="subscript">b</sub>(n) =
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log(n)/log(b)，其中 log 是自然对数。
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</td>
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</tr>
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</tbody>
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</table>
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</p>
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</div>
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<div class="refsect1 seealso" id="refsect1-function.log-seealso">
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<h3 class="title">参见</h3>
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<p class="para">
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<ul class="simplelist">
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<li class="member"><span class="function"><a href="log10.html" class="function" rel="rdfs-seeAlso">log10()</a> - 以 10 为底的对数</span></li>
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<li class="member"><span class="function"><a href="exp.html" class="function" rel="rdfs-seeAlso">exp()</a> - 计算 e 的指数</span></li>
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<li class="member"><span class="function"><a href="pow.html" class="function" rel="rdfs-seeAlso">pow()</a> - 指数表达式</span></li>
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</ul>
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</p>
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</div>
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</div></div></div></body></html> |