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<title>GNU Scientific Library &ndash; Reference Manual: An Example Program</title>

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<a name="An-Example-Program"></a>
<div class="header">
<p>
Next: <a href="Compiling-and-Linking.html#Compiling-and-Linking" accesskey="n" rel="next">Compiling and Linking</a>, Up: <a href="Using-the-library.html#Using-the-library" accesskey="u" rel="up">Using the library</a> &nbsp; [<a href="Function-Index.html#Function-Index" title="Index" rel="index">Index</a>]</p>
</div>
<hr>
<a name="An-Example-Program-1"></a>
<h3 class="section">2.1 An Example Program</h3>

<p>The following short program demonstrates the use of the library by
computing the value of the Bessel function <em>J_0(x)</em> for <em>x=5</em>,
</p>
<div class="example">
<pre class="verbatim">#include &lt;stdio.h&gt;
#include &lt;gsl/gsl_sf_bessel.h&gt;

int
main (void)
{
  double x = 5.0;
  double y = gsl_sf_bessel_J0 (x);
  printf (&quot;J0(%g) = %.18e\n&quot;, x, y);
  return 0;
}
</pre></div>

<p>The output is shown below, and should be correct to double-precision
accuracy,<a name="DOCF2" href="#FOOT2"><sup>2</sup></a>
</p>
<div class="example">
<pre class="verbatim">J0(5) = -1.775967713143382642e-01
</pre></div>

<p>The steps needed to compile this program are described
in the following sections.
</p>
<div class="footnote">
<hr>
<h4 class="footnotes-heading">Footnotes</h4>

<h3><a name="FOOT2" href="#DOCF2">(2)</a></h3>
<p>The last few digits may vary slightly depending on
the compiler and platform used&mdash;this is normal.</p>
</div>



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