SIR equations in the vignette

[choisy]

I am a bit concerned by the equations of the SIR model in the vignette. In particular, when you use parameter, it is very important that it clear to every body whether you're talking about rate in continuous time or probabilities in discrete time. There is of course a relationship between the two but this relationship is not linear, particularly when the time step is long respective to the frequency of occurrence of the process. What worries me here is that (i) on the diagram I have the impression that, implicitly, you are in continuous time and thus parameters are rates and, at the same time, (ii) on the equations you are clearly in discrete time and thus the parameters should be probabilities right? But, yet, it still seems that they are rates.