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<title>GNU Scientific Library &ndash; Reference Manual: Special Functions Examples</title>

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<a name="Special-Functions-Examples"></a>
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<p>
Next: <a href="Special-Functions-References-and-Further-Reading.html#Special-Functions-References-and-Further-Reading" accesskey="n" rel="next">Special Functions References and Further Reading</a>, Previous: <a href="Zeta-Functions.html#Zeta-Functions" accesskey="p" rel="previous">Zeta Functions</a>, Up: <a href="Special-Functions.html#Special-Functions" accesskey="u" rel="up">Special Functions</a> &nbsp; [<a href="Function-Index.html#Function-Index" title="Index" rel="index">Index</a>]</p>
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<hr>
<a name="Examples-2"></a>
<h3 class="section">7.33 Examples</h3>

<p>The following example demonstrates the use of the error handling form of
the special functions, in this case to compute the Bessel function
<em>J_0(5.0)</em>,
</p>
<div class="example">
<pre class="verbatim">#include &lt;stdio.h&gt;
#include &lt;gsl/gsl_errno.h&gt;
#include &lt;gsl/gsl_sf_bessel.h&gt;

int
main (void)
{
  double x = 5.0;
  gsl_sf_result result;

  double expected = -0.17759677131433830434739701;
  
  int status = gsl_sf_bessel_J0_e (x, &amp;result);

  printf (&quot;status  = %s\n&quot;, gsl_strerror(status));
  printf (&quot;J0(5.0) = %.18f\n&quot;
          &quot;      +/- % .18f\n&quot;, 
          result.val, result.err);
  printf (&quot;exact   = %.18f\n&quot;, expected);
  return status;
}
</pre></div>

<p>Here are the results of running the program,
</p>
<div class="example">
<pre class="example">$ ./a.out 
</pre><pre class="verbatim">status  = success
J0(5.0) = -0.177596771314338264
      +/-  0.000000000000000193
exact   = -0.177596771314338292
</pre></div>

<p>The next program computes the same quantity using the natural form of
the function. In this case the error term <var>result.err</var> and return
status are not accessible.
</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 expected = -0.17759677131433830434739701;
  
  double y = gsl_sf_bessel_J0 (x);

  printf (&quot;J0(5.0) = %.18f\n&quot;, y);
  printf (&quot;exact   = %.18f\n&quot;, expected);
  return 0;
}
</pre></div>

<p>The results of the function are the same,
</p>
<div class="example">
<pre class="example">$ ./a.out 
</pre><pre class="verbatim">J0(5.0) = -0.177596771314338264
exact   = -0.177596771314338292
</pre></div>






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