..' can   generate back the matrix and
                  the exact position of the variable ...
               </li>
            </ul>
         </div><pre> penm.Y{1} = ones(3);
 penm.Y{2} = spones(sprandsym(5,0.3));
 penm.Y{3} = spones(sprand(6,6,0.2));</pre><p><b>Define box constraints on variables</b></p>
         <div>
            <ul>
               <li> <b>box constraints</b> (lower/upper bounds) on the variables, <tt>lbx &lt;= x &lt;= ubx</tt>. If <tt>lbx = -Inf</tt>, it is not considered; similarly f