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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> [<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 <stdio.h>
#include <gsl/gsl_errno.h>
#include <gsl/gsl_sf_bessel.h>
int
main (void)
{
double x = 5.0;
gsl_sf_result result;
double expected = -0.17759677131433830434739701;
int status = gsl_sf_bessel_J0_e (x, &result);
printf ("status = %s\n", gsl_strerror(status));
printf ("J0(5.0) = %.18f\n"
" +/- % .18f\n",
result.val, result.err);
printf ("exact = %.18f\n", 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 <stdio.h>
#include <gsl/gsl_sf_bessel.h>
int
main (void)
{
double x = 5.0;
double expected = -0.17759677131433830434739701;
double y = gsl_sf_bessel_J0 (x);
printf ("J0(5.0) = %.18f\n", y);
printf ("exact = %.18f\n", 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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