<span class="math display">\[ \mathrm{rising\_factorial}(x,n) = \begin{cases} x^{(n)}
&amp; \text{if } x &gt; 0 \\ \textrm{error} &amp; \text{if } x \leq 0 \end{cases}
\]</span> where <span class="math display">\[ x^{(n)}=\frac{\Gamma(x+n)}{\Gamma(x)} \]</span></p>
<!-- real; log_rising_factorial; (real x, real n); -->
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<p><code>real</code> <strong><code>log_rising_factorial</code></strong><code>(real x, real n)</code><br>
Return the log of the rising factorial of x with power n defined for
positive 