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<title>GNU Scientific Library – Reference Manual: Infinities and Not-a-number</title>
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<a name="Infinities-and-Not_002da_002dnumber"></a>
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<p>
Next: <a href="Elementary-Functions.html#Elementary-Functions" accesskey="n" rel="next">Elementary Functions</a>, Previous: <a href="Mathematical-Constants.html#Mathematical-Constants" accesskey="p" rel="previous">Mathematical Constants</a>, Up: <a href="Mathematical-Functions.html#Mathematical-Functions" accesskey="u" rel="up">Mathematical Functions</a> [<a href="Function-Index.html#Function-Index" title="Index" rel="index">Index</a>]</p>
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<hr>
<a name="Infinities-and-Not_002da_002dnumber-1"></a>
<h3 class="section">4.2 Infinities and Not-a-number</h3>
<a name="index-infinity_002c-defined-as-a-macro"></a>
<a name="index-IEEE-infinity_002c-defined-as-a-macro"></a>
<a name="index-NaN_002c-defined-as-a-macro"></a>
<a name="index-Not_002da_002dnumber_002c-defined-as-a-macro"></a>
<a name="index-IEEE-NaN_002c-defined-as-a-macro"></a>
<dl>
<dt><a name="index-GSL_005fPOSINF"></a>Macro: <strong>GSL_POSINF</strong></dt>
<dd><p>This macro contains the IEEE representation of positive infinity,
<em>+\infty</em>. It is computed from the expression <code>+1.0/0.0</code>.
</p></dd></dl>
<dl>
<dt><a name="index-GSL_005fNEGINF"></a>Macro: <strong>GSL_NEGINF</strong></dt>
<dd><p>This macro contains the IEEE representation of negative infinity,
<em>-\infty</em>. It is computed from the expression <code>-1.0/0.0</code>.
</p></dd></dl>
<dl>
<dt><a name="index-GSL_005fNAN"></a>Macro: <strong>GSL_NAN</strong></dt>
<dd><p>This macro contains the IEEE representation of the Not-a-Number symbol,
<code>NaN</code>. It is computed from the ratio <code>0.0/0.0</code>.
</p></dd></dl>
<dl>
<dt><a name="index-gsl_005fisnan"></a>Function: <em>int</em> <strong>gsl_isnan</strong> <em>(const double <var>x</var>)</em></dt>
<dd><p>This function returns 1 if <var>x</var> is not-a-number.
</p></dd></dl>
<dl>
<dt><a name="index-gsl_005fisinf"></a>Function: <em>int</em> <strong>gsl_isinf</strong> <em>(const double <var>x</var>)</em></dt>
<dd><p>This function returns <em>+1</em> if <var>x</var> is positive infinity,
<em>-1</em> if <var>x</var> is negative infinity and 0
otherwise.<a name="DOCF6" href="#FOOT6"><sup>6</sup></a>
</p></dd></dl>
<dl>
<dt><a name="index-gsl_005ffinite"></a>Function: <em>int</em> <strong>gsl_finite</strong> <em>(const double <var>x</var>)</em></dt>
<dd><p>This function returns 1 if <var>x</var> is a real number, and 0 if it is
infinite or not-a-number.
</p></dd></dl>
<div class="footnote">
<hr>
<h4 class="footnotes-heading">Footnotes</h4>
<h3><a name="FOOT6" href="#DOCF6">(6)</a></h3>
<p>Note that the C99 standard only requires the
system <code>isinf</code> function to return a non-zero value, without the
sign of the infinity. The implementation in some earlier versions of
GSL used the system <code>isinf</code> function and may have this behavior
on some platforms. Therefore, it is advisable to test the sign of
<var>x</var> separately, if needed, rather than relying the sign of the
return value from <code>gsl_isinf()</code>.</p>
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