rigamma function is the second
derivative of the natural logarithm of the Gamma function</p>
<!-- real; lmgamma; (int n, real x); -->
<p></p>
<p><code>real</code> <strong><code>lmgamma</code></strong><code>(int n, real x)</code><br>
Return the natural logarithm of the multivariate gamma function
<span class="math inline">\(\Gamma_n\)</span> with n dimensions applied to x. <span class="math display">\[ \text{lmgamma}(n,x) =
\begin{cases} \frac{n(n-1)}{4} \log \pi + \sum_{j=1}^n \log
\Gamma\left(x + \frac{1 -