Figure 2
From: A Viral Infection Model with a Nonlinear Infection Rate
Illustrations of the Allee effect for (1. 5). Here, 
. 
is stable, 
is a saddle point, 
is stable. Note that SM is the stable manifolds of 
(solid line), UM is the unstable manifolds of 
(dash line), and the phase portrait of (1.6) is divided into two domains of extinction and persistence of the virus by SM.