row vector and <code>a[1, 1]</code> a real value. Matrices implicitly have two indexing dimensions. The type declaration <code>matrix[ , ] b</code> specifies that <code>b</code> is a two-dimensional array of matrices, for a total of four indexing dimensions, with <code>b[1, 1, 1, 1]</code> picking out a real value.</p>
</section>
<section id="dimensionality-checks-and-exceptions" class="level3 unnumbered">
<h3 class="unnumbered anchored" data-anchor-id="dimensionality-checks-and-exceptions">Dimensionality c