ubmatrices (i.e., <strong>U</strong>,
<strong>F</strong> or <strong>C</strong>) of the matrix model, but other
submatrices are complete. For example, there may be <code>NA</code>
entries in the <strong>F</strong> submatrix, while the
<strong>U</strong> matrix remains complete. These issues are flagged
with the columns <code>check_NA_A</code>, <code>check_NA_U</code>,
<code>check_NA_F</code> and <code>check_NA_C</code>.</p>
</div>
<div class="section level3">
<h3 id="excessive-zeros">Excessive zeros<a class=