$R_{h}$ and makes some of the functions strictly convex.
The authors then apply a classical dual based approach with Lagrange multiplier
-to solve such a problem~\cite{}.
+to solve such a problem~\cite{PM06}.
They first introduce dual variables
$u_{hi}$, $v_{h}$, $\lambda_{i}$, and $w_l$ for any
$h \in V$, $ i \in N$, and $l \in L$.
