verse transform reverses the two steps of the transform.
Given an unconstrained lower-triangular <span class="math inline">\(K \times K\)</span> matrix <span class="math inline">\(y\)</span>, the
first step is to recover the intermediate matrix <span class="math inline">\(z\)</span> by reversing the
log transform,</p>
<p><span class="math display">\[
z_{m,n} =
\left\{
\begin{array}{cl}
0 &amp; \mbox{if } m &lt; n,
\\
\exp(y_{m,m}) &amp; \mbox{if } m = n, \mbox{ and}
\\
y_{m,n} &amp; \mbox{if } m &gt; n.
\en