exist).</p>
<p>Although ranks are usually (unless ties exist) integral values from
   1 to N, it is to be noted that they are outputted as REAL values in
   the vector XR.  XR is so as to be consistent with the fact that all
   vector arguments in all other datapac subroutines are REAL; but more
   importantly, because ties frequently do exist in data sets and so some
   of the resulting ranks will be non-integral and so the output vector
   of ranks must necessarily be REAL and not INTEGER.</p>
<p>The inpu