ght)!}. \]</span></p>
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<p></p>
<p><code>real</code> <strong><code>bessel_first_kind</code></strong><code>(int v, real x)</code><br>
Return the Bessel function of the first kind with order v applied to
x. <span class="math display">\[ \mathrm{bessel\_first\_kind}(v,x) = J_v(x), \]</span> where <span class="math display">\[
J_v(x)=\left(\frac{1}{2}x\right)^v \sum_{k=0}^\infty
\frac{\left(-\frac{1}{4}x^2\right)^k}{k!\, \Gamma(v+k+1)} \]</span></p>
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