. In Table 0.0, we compare the exact solution with the approximate one obtained by the scheme . We report the approximation error for ${\lambda}_0$ and $w_0$ (in $L^\infty$-norm and $L^0$-norm) and the order of convergence for ${\lambda}_0$. We can observe an order of convergence close to $0$ for ${\lambda}_0$ and therefore equivalent to one obtained by discretization of the Rayleigh quotient via finite elements