Numerical solutions of the cubic–quintic NSE by symplectic method with θ = 45.18°, q = 0.925, and different parameter g. Panels (a), (d), (g), and (j) are the phase trajectories, panels (b), (e), (h), and (k) are the time evolutions of A(L/2, t), and panels (c), (f), (i), and (l) are the corresponding Fourier spectra.