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<a name="erf_002c-erff_002c-erfc_002c-erfcf_002d_002d_002derror-function"></a>
<h3 class="section">1.14 <code>erf</code>, <code>erff</code>, <code>erfc</code>, <code>erfcf</code>&mdash;error function</h3>
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<p><strong>Synopsis</strong>
</p><div class="example">
<pre class="example">#include &lt;math.h&gt;
double erf(double <var>x</var>);
float erff(float <var>x</var>);
double erfc(double <var>x</var>);
float erfcf(float <var>x</var>);

</pre></div>
<p><strong>Description</strong><br>
<code>erf</code> calculates an approximation to the &ldquo;error function&rdquo;,
which estimates the probability that an observation will fall within
<var>x</var> standard deviations of the mean (assuming a normal
distribution).
</p>
<p><code>erfc</code> calculates the complementary probability; that is,
<code>erfc(<var>x</var>)</code> is <code>1 - erf(<var>x</var>)</code>.  <code>erfc</code> is computed directly,
so that you can use it to avoid the loss of precision that would
result from subtracting large probabilities (on large <var>x</var>) from 1.
</p>
<p><code>erff</code> and <code>erfcf</code> differ from <code>erf</code> and <code>erfc</code> only in the
argument and result types.
</p>
<br>
<p><strong>Returns</strong><br>
For positive arguments, <code>erf</code> and all its variants return a
probability&mdash;a number between 0 and 1.
</p>
<br>
<p><strong>Portability</strong><br>
None of the variants of <code>erf</code> are ANSI C.
</p>
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