not be assigned a row vector or
vice versa.</p>
<pre class="stan"><code>matrix[1,4] a;
row_vector[4] b;
// ...
a = b;  // illegal assignment of row vector to matrix
b = a;  // illegal assignment of matrix to row vector</code></pre>
<p>Similarly, an <span class="math inline">\(M \times 1\)</span> matrix may not be assigned to a column vector.</p>
<pre class="stan"><code>matrix[4,1] a;
vector[4] b;
// ...
a = b;  // illegal assignment of column vector to matrix
b = a;  // illegal assignment of matrix to colum