Figure 2From: Hopf bifurcation of a heroin model with time delay and saturated treatment functionPhase portrait of system (15) with \(\tau = 37.45 < \tau_{0} =40.1285\): (a) \(S - U_{1} -U_{2}\), (b) \(S - U_{1} -U_{3}\), (c) \(S - U_{2} -U_{3}\), (d) \(U_{1} -U_{2}-U_{3}\)Back to article page