“…By using the qualitative theory of differential equations [22,27,29], we can see that if J(𝜙 i , 0) < 0, the equilibrium point (𝜙 i , 0) is a saddle; if J(𝜙 i , 0) > 0, the equilibrium point (𝜙 i , 0) is a center; if J(𝜙 i , 0) = 0 and the index of equilibrium point (𝜙 i , 0) is 0, then it is a cusp. Using the above qualitative analysis, phase portraits of the system can be obtained under different parameters, as shown in Figures 1,4, and 6.…”