 suppose <span class="math inline">\(y\)</span> is a vector
containing <span class="math inline">\(\binom{K}{2}\)</span> unconstrained values. These are first
transformed via the bijective function <span class="math inline">\(\tanh : \mathbb{R} \rightarrow (-1, 1)\)</span></p>
<p><span class="math display">\[
\tanh x = \frac{\exp(2x) - 1}{\exp(2x) + 1}.
\]</span></p>
<p>Then, define a <span class="math inline">\(K \times K\)</span> matrix <span class="math inline">\(z\)</span>, the upper triangular values o