$$\begin{tabular} {\vert c\vert c\vert c\vert c\vert} \hline\h... ... $\delta^2$& $E- 2 +E^{-1}$& $-4\S$\ \hline\hline\end{tabular}$$

$$\begin{tabular} {\vert c\vert c\vert} \hline\hline \multicol... ...{\rm d}^2\ \over\strut{\rm d} x^2}$\ \hline\hline\end{tabular}$$

Note: $\xi = k \Delta x$, where k is the wave number.