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<h1 class="refname">log</h1>
<p class="verinfo">(PHP 4, PHP 5)</p><p class="refpurpose"><span class="refname">log</span> — <span class="dc-title">Natural logarithm</span></p>
</div>
<div class="refsect1 description" id="refsect1-function.log-description">
<h3 class="title">Description</h3>
<div class="methodsynopsis dc-description">
<span class="type">float</span> <span class="methodname"><strong>log</strong></span>
( <span class="methodparam"><span class="type">float</span> <code class="parameter">$arg</code></span>
[, <span class="methodparam"><span class="type">float</span> <code class="parameter">$base</code><span class="initializer"> = M_E</span></span>
] )</div>
<p class="para rdfs-comment">
If the optional <em><code class="parameter">base</code></em> parameter is specified,
<span class="function"><strong>log()</strong></span> returns log<sub class="subscript">base</sub>
<em><code class="parameter">arg</code></em>, otherwise <span class="function"><strong>log()</strong></span>
returns the natural logarithm of <em><code class="parameter">arg</code></em>.
</p>
</div>
<div class="refsect1 parameters" id="refsect1-function.log-parameters">
<h3 class="title">Parameters</h3>
<p class="para">
<dl>
<dt>
<span class="term"><em><code class="parameter">arg</code></em></span>
<dd>
<p class="para">
The value to calculate the logarithm for
</p>
</dd>
</dt>
<dt>
<span class="term"><em><code class="parameter">base</code></em></span>
<dd>
<p class="para">
The optional logarithmic base to use
(defaults to 'e' and so to the natural logarithm).
</p>
</dd>
</dt>
</dl>
</p>
</div>
<div class="refsect1 returnvalues" id="refsect1-function.log-returnvalues">
<h3 class="title">Return Values</h3>
<p class="para">
The logarithm of <em><code class="parameter">arg</code></em> to
<em><code class="parameter">base</code></em>, if given, or the
natural logarithm.
</p>
</div>
<div class="refsect1 changelog" id="refsect1-function.log-changelog">
<h3 class="title">Changelog</h3>
<p class="para">
<table class="doctable informaltable">
<thead>
<tr>
<th>Version</th>
<th>Description</th>
</tr>
</thead>
<tbody class="tbody">
<tr>
<td>4.3.0</td>
<td>
The optional parameter <em><code class="parameter">base</code></em> became available.
For older versions you can calculate the logarithm in base <em>b</em>
of a number <em>n</em>, but using the mathematical identity:
log<sub class="subscript">b</sub>(n) = log(n)/log(b), where log is the
neperian (or natural) logarithm.
</td>
</tr>
</tbody>
</table>
</p>
</div>
<div class="refsect1 seealso" id="refsect1-function.log-seealso">
<h3 class="title">See Also</h3>
<p class="para">
<ul class="simplelist">
<li class="member"> <span class="function"><a href="function.log10.html" class="function" rel="rdfs-seeAlso">log10()</a> - Base-10 logarithm</span></li>
<li class="member"> <span class="function"><a href="function.exp.html" class="function" rel="rdfs-seeAlso">exp()</a> - Calculates the exponent of e</span></li>
<li class="member"> <span class="function"><a href="function.pow.html" class="function" rel="rdfs-seeAlso">pow()</a> - Exponential expression</span></li>
</ul>
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