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<title>The GNU Fortran Compiler: BESSEL_J1</title>

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<a name="BESSEL_005fJ1-_002d_002d_002d-Bessel-function-of-the-first-kind-of-order-1"></a>
<h3 class="section">9.41 <code>BESSEL_J1</code> &mdash; Bessel function of the first kind of order 1</h3>
<a name="index-BESSEL_005fJ1"></a>
<a name="index-BESJ1"></a>
<a name="index-DBESJ1"></a>
<a name="index-Bessel-function_002c-first-kind-1"></a>

<dl compact="compact">
<dt><em>Description</em>:</dt>
<dd><p><code>BESSEL_J1(X)</code> computes the Bessel function of the first kind of
order 1 of <var>X</var>. This function is available under the name
<code>BESJ1</code> as a GNU extension.
</p>
</dd>
<dt><em>Standard</em>:</dt>
<dd><p>Fortran 2008
</p>
</dd>
<dt><em>Class</em>:</dt>
<dd><p>Elemental function
</p>
</dd>
<dt><em>Syntax</em>:</dt>
<dd><p><code>RESULT = BESSEL_J1(X)</code>
</p>
</dd>
<dt><em>Arguments</em>:</dt>
<dd><table>
<tr><td width="15%"><var>X</var></td><td width="70%">The type shall be <code>REAL</code>.</td></tr>
</table>

</dd>
<dt><em>Return value</em>:</dt>
<dd><p>The return value is of type <code>REAL</code> and lies in the
range <em>- 0.5818... \leq Bessel (0,x) \leq 0.5818 </em>. It has the same
kind as <var>X</var>.
</p>
</dd>
<dt><em>Example</em>:</dt>
<dd><div class="smallexample">
<pre class="smallexample">program test_besj1
  real(8) :: x = 1.0_8
  x = bessel_j1(x)
end program test_besj1
</pre></div>

</dd>
<dt><em>Specific names</em>:</dt>
<dd><table>
<tr><td width="20%">Name</td><td width="20%">Argument</td><td width="20%">Return type</td><td width="25%">Standard</td></tr>
<tr><td width="20%"><code>DBESJ1(X)</code></td><td width="20%"><code>REAL(8) X</code></td><td width="20%"><code>REAL(8)</code></td><td width="25%">GNU extension</td></tr>
</table>
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