Figure 4From: Complex dynamics in an SIS epidemic model with nonlinear incidenceWhen \(R_{0}=1\), and \(\varLambda>(1-\sigma)/a\). (a) \(\psi_{4}<0\), the disease-free equilibrium \(E_{0}\) is unstable and the unique positive equilibrium \(E_{4}\) is globally stable. (b) \(\psi_{4}>0\), \(E_{0}\) and \(E_{4}\) are unstable and there exists a stable limit cycleBack to article page