FIG. 6.

Quasiperiodic attractors for $ϵ=0.179$ [panels (a) and (b)] and $ϵ=0.2$ [panels (c) and (d)]. Time series of primary infectives (log variables) are shown in (a) and (c). Phase differences of primary infectives $x_2,x_3,x_4$ relative to primary infective $x_1$ are shown in (b) and (d). The time series in (a) and (c) are the beginning of those used to generate (b) and (d). The reference strain $x_1$ is the lightest gray curve in (a) and (c). Other parameters: $\varphi =1$.