\[\mathcal{E}\left(x,k\right)=-\int_{0}^{x}\left({\operatorname{ds}}^{2}\left(t,%
k\right)-t^{-2}\right)\,\mathrm{d}t+x^{-1}+{k^{\prime}}^{2}x-\operatorname{cn}%
\left(x,k\right)\operatorname{ds}\left(x,k\right),\]