Positive Periodic Solutions of an Epidemic Model with Seasonality

Figure 5

Phase plane of 𝑆(𝑡) and 𝐼(𝑡). When the parameter values are 𝑟=0.13, 𝑎=0.36, and 𝑏=0.2, 𝑅₀=1.0834, 𝑅_𝑑=1.3>1, 𝑅_𝑑>𝑅^𝑢₁=1.0435, and 𝑅_𝑑>𝑅^𝑙₁=1.029. The value of other parameters can be seen in Table 1.