Figure 4.

A two-parameter sensitivity analysis of ${\displaystyle {\mathcal{R}}_c}$ respect to ${\displaystyle u_1}$ and ${\displaystyle u_2}$ under the impact of ${\displaystyle \xi }$ given in panel (a). The orange region represents an ${\displaystyle {\mathcal{R}}_c}$ domain that is always larger than 1, while blue is always smaller than 1, independent of the value of ${\displaystyle \xi }$ . The grey region represents the area of ${\displaystyle {\mathcal{R}}_c}$ that may change from greater than 1 to smaller than 1 as ${\displaystyle \xi }$ increases. Panels (b) to (d), show the dynamics of ${\displaystyle S}$ and ${\displaystyle I_1}$ for sample points ${\displaystyle P_1}$ , ${\displaystyle P_2}$ and ${\displaystyle P_3}$ , respectively.