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<a name="atanh_002c-atanhf_002d_002d_002dinverse-hyperbolic-tangent"></a>
<h3 class="section">1.9 <code>atanh</code>, <code>atanhf</code>&mdash;inverse hyperbolic tangent</h3>
<a name="index-atanh"></a>
<a name="index-atanhf"></a>
<p><strong>Synopsis</strong>
</p><div class="example">
<pre class="example">#include &lt;math.h&gt;
double atanh(double <var>x</var>);
float atanhf(float <var>x</var>);

</pre></div>
<p><strong>Description</strong><br>
<code>atanh</code> calculates the inverse hyperbolic tangent of <var>x</var>.
</p>
<p><code>atanhf</code> is identical, other than taking and returning
<code>float</code> values.
</p>
<br>
<p><strong>Returns</strong><br>
<code>atanh</code> and <code>atanhf</code> return the calculated value.
</p>
<p>If 
</p><div class="smallexample">
<pre class="smallexample"><var>x</var>|
</pre></div>
<p>is greater than 1, the global <code>errno</code> is set to <code>EDOM</code> and
the result is a NaN.  A <code>DOMAIN error</code> is reported.
</p>
<p>If 
</p><div class="smallexample">
<pre class="smallexample"><var>x</var>|
</pre></div>
<p>is 1, the global <code>errno</code> is set to <code>EDOM</code>; and the result is 
infinity with the same sign as <code>x</code>.  A <code>SING error</code> is reported.
</p>
<br>
<p><strong>Portability</strong><br>
Neither <code>atanh</code> nor <code>atanhf</code> are ANSI C.
</p>
<br>


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