Figure 12.

In Figure 10 and Figure 11, the roots are not exactly on the unit circle—here, $\Delta t$ dependence of $\left|{\xi }_0\right|$ and $\left|{\xi }_{\pm }\right|$ is displayed, at a neutral value $k\Delta x=\pi /4$, for $\widehat{C}=1$ and $\alpha =1/2$.