or almost all <code>Rage</code>
functions that the matrices used as arguments do not include
<code>NA</code> values. With divided (split) matrices, <code>NA</code>
values may be present in some submatrices but not others. For example,
the <strong>U</strong> matrix may be complete, but the
<strong>F</strong> matrix may have <code>NA</code> values. In this case,
functions that require an <strong>F</strong> matrix will fail, while
those that only require a <strong>U</strong> matrix will work. Users
should filt