Eckhaus Instability - Dependence on Wavevector

The control parameter is eps=0.35 for which the Eckhaus instability occurs at q=1.17. These demonstrations compare how the one dimensional instability develops as the background wave number varies (q=1.17810 and q=1.20264 are used). Reset a few times to sample different random initial conditions. What do you notice about how the instability develops in the two cases? Compare with the theoretical expectations.

Note: in the FFT plots for this example only the dependence on the x-component of the wave number is plotted