t produces an
indexable position in the result. To evaluate that index position in
the result, the index is first passed to the multiple index, and the
resulting index used.</p>
<pre class="stan"><code>a[idxs, ...][i, ...] = a[idxs[i], ...][...]</code></pre>
<p>On the other hand, if <code>idx</code> is a single index, it reduces the
dimensionality of the output, so that</p>
<pre class="stan"><code>a[idx, ...] = a[idx][...]</code></pre>
<p>The only issue is what happens with matrices and vectors. Vectors
wor