</tt>)   as a (possibly sparse) matrix <tt>ddgk</tt> of dimensions   <tt>(Nx+NYnnz) x (Nx+NYnnz)</tt>; if <tt>NgNLN = 0</tt>, <tt>conhess()</tt> needn't be defined.
               </li>
            </ul>
         </div>
         <p>Alternatively, it is possible to specify <tt>lagrhess()</tt> callback instead of <tt>objhess()</tt> and <tt>conhess()</tt> which returns the hessian of the Lagrangian
         </p><pre>   ddL = hess F(x,Y) + sum_{k=1}^{NgNLN} v(k) * hess g_k(x,Y)</pre><p>as a (possibly sparse) ma