2.2.1. Chaotic Trajectory

For a chaotic system, the trajectory on the phase plane can show the randomness of outputs [25]. The larger the space occupied by the trajectory, the better the random outputs of the chaotic systems. Figure 3 shows the trajectories of TDSCL, DLCL, and LSMCL. The trajectory of TDSCL can fill the entire phase space compared to DLCL and LSMCL. This indicates that the sequence generated by the TDSCL chaotic map has better randomness and ergodicity.

**Figure 3.** Trajectories for (**a**) TDSCL with *μ* = 1, (**b**) delay and linearly coupled logistic chaotic map (DLCL) with *μ* = 1 , and (**c**) logistic-modulated sine-coupling logistic chaotic map (LSMCL) with *θ* = 0.75.
