 j}{2}\right) &amp; \text{if } x\not\in
\{\dots,-3,-2,-1,0\}\\ \textrm{error} &amp; \text{otherwise} \end{cases}
\]</span></p>
<!-- real; gamma_p; (real a, real z); -->
<p></p>
<p><code>real</code> <strong><code>gamma_p</code></strong><code>(real a, real z)</code><br>
Return the normalized lower incomplete gamma function of a and z
defined for positive a and nonnegative z. <span class="math display">\[ \mathrm{gamma\_p}(a,z) =
\begin{cases} \frac{1}{\Gamma(a)}\int_0^zt^{a-1}e^{-t}dt &amp; \text{if }
a &gt; 