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<title>Returns log(1 + number), computed in a way that is accurate even when
the value of number is close to zero</title>
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<h1 class="refname">log1p</h1>
<p class="verinfo">(PHP 4 >= 4.1.0, PHP 5)</p><p class="refpurpose"><span class="refname">log1p</span> — <span class="dc-title">
Returns log(1 + number), computed in a way that is accurate even when
the value of number is close to zero
</span></p>
</div>
<div class="refsect1 description" id="refsect1-function.log1p-description">
<h3 class="title">Description</h3>
<div class="methodsynopsis dc-description">
<span class="type">float</span> <span class="methodname"><strong>log1p</strong></span>
( <span class="methodparam"><span class="type">float</span> <code class="parameter">$number</code></span>
)</div>
<p class="para rdfs-comment">
<span class="function"><strong>log1p()</strong></span> returns log(1 +
<em><code class="parameter">number</code></em>) computed in a way that is accurate even
when the value of <em><code class="parameter">number</code></em> is close to zero.
<span class="function"><a href="function.log.html" class="function">log()</a></span> might only return log(1) in this case
due to lack of precision.
</p>
</div>
<div class="refsect1 parameters" id="refsect1-function.log1p-parameters">
<h3 class="title">Parameters</h3>
<p class="para">
<dl>
<dt>
<span class="term"><em><code class="parameter">number</code></em></span>
<dd>
<p class="para">
The argument to process
</p>
</dd>
</dt>
</dl>
</p>
</div>
<div class="refsect1 returnvalues" id="refsect1-function.log1p-returnvalues">
<h3 class="title">Return Values</h3>
<p class="para">
log(1 + <em><code class="parameter">number</code></em>)
</p>
</div>
<div class="refsect1 changelog" id="refsect1-function.log1p-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>5.3.0</td>
<td>
This function is now available on all platforms
</td>
</tr>
</tbody>
</table>
</p>
</div>
<div class="refsect1 seealso" id="refsect1-function.log1p-seealso">
<h3 class="title">See Also</h3>
<p class="para">
<ul class="simplelist">
<li class="member"> <span class="function"><a href="function.expm1.html" class="function" rel="rdfs-seeAlso">expm1()</a> - Returns exp(number) - 1, computed in a way that is accurate even
when the value of number is close to zero</span></li>
<li class="member"> <span class="function"><a href="function.log.html" class="function" rel="rdfs-seeAlso">log()</a> - Natural logarithm</span></li>
<li class="member"> <span class="function"><a href="function.log10.html" class="function" rel="rdfs-seeAlso">log10()</a> - Base-10 logarithm</span></li>
</ul>
</p>
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