each individual column within
   the panel.
   The location of the first nonzero in each supernodal segment
   (supernodal entry location) is also returned. Each column has a
   separate list for this purpose.</pre><p>
<pre>   Two marker arrays are used for dfs:
     marker[i] == jj, if i was visited during dfs of current column jj;
     marker1[i] &gt;= jcol, if i was visited by earlier columns in this panel;</pre><p>
<pre>   marker: A-row --&gt; A-row/col (0/1)
   repfnz: SuperA-col --&gt; PA-row
   paren