</code>, providing that <code>x</code>
and <code>y</code> are primitive variables.</p>
</div>
<div id="matrix-expressions" class="section level3 unnumbered">
<h3>Matrix expressions</h3>
<p>A matrix expression consists of square brackets wrapped
around a sequence of comma separated row vector expressions.
This syntax provides a way declare and define a matrix in a single
line, as follows.</p>
<pre class="stan"><code>matrix[3,2] m1 = [ [ 1, 2 ], [ 3, 4 ], [5, 6 ] ];</code></pre>
<p>Any expression denoting a r