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<title>Special Function Usage - GNU Scientific Library -- Reference Manual</title>
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<a name="Special-Function-Usage"></a>
Next: <a rel="next" accesskey="n" href="The-gsl_005fsf_005fresult-struct.html">The gsl_sf_result struct</a>,
Up: <a rel="up" accesskey="u" href="Special-Functions.html">Special Functions</a>
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<h3 class="section">7.1 Usage</h3>
<p>The special functions are available in two calling conventions, a
<dfn>natural form</dfn> which returns the numerical value of the function and
an <dfn>error-handling form</dfn> which returns an error code. The two types
of function provide alternative ways of accessing the same underlying
code.
<p>The <dfn>natural form</dfn> returns only the value of the function and can be
used directly in mathematical expressions. For example, the following
function call will compute the value of the Bessel function
J_0(x),
<pre class="example"> double y = gsl_sf_bessel_J0 (x);
</pre>
<p class="noindent">There is no way to access an error code or to estimate the error using
this method. To allow access to this information the alternative
error-handling form stores the value and error in a modifiable argument,
<pre class="example"> gsl_sf_result result;
int status = gsl_sf_bessel_J0_e (x, &result);
</pre>
<p class="noindent">The error-handling functions have the suffix <code>_e</code>. The returned
status value indicates error conditions such as overflow, underflow or
loss of precision. If there are no errors the error-handling functions
return <code>GSL_SUCCESS</code>.
<hr>The GNU Scientific Library - a free numerical library licensed under the GNU GPL<br>Back to the <a href="/software/gsl/">GNU Scientific Library Homepage</a></body></html>
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