Figure 1
Three typical periodic solutions of Eq. (8) with \(y=z=0\), (a,d) condition (2.3) under \(\delta _1=\delta _4=2,\delta _2=\delta _3=1,\omega _1=2,\omega _2=3,\omega _3=1/2,k_1=k_4=1,k_3=2,p_2=3,\) (b,e) condition (2.3) under \(\delta _1=1/2,\delta _2=\delta _3=1,\delta _4=2,\omega _2=1,k_1=1,k_3=k_4=2,p_2=1,\) (c,f) condition (10) under \(\delta _1=1/2,\delta _2=\delta _3=1,\delta _4=2,\omega _2=1,k_1=1,k_3=k_4=2,p_2=1\).
