code>x[1]</code> is a <code>J</code> by <code>K</code>
array, as is <code>y</code>.</p>
<p>Partial array assignment also works for arrays of matrices, vectors,
and row vectors.</p>
</div>
<div id="mixing-array-vector-and-matrix-types" class="section level3 unnumbered">
<h3>Mixing Array, Vector, and Matrix Types</h3>
<p>Arrays, row vectors, column vectors and matrices are not
interchangeable in Stan. Thus a variable of any one of these
fundamental types is not assignable to any of the others, nor may it
be u