A straight forward computation shows that models (1) &
(2) are continuous and Lipschizian in ℝ_
` . From the existence
and uniqueness of solution of the ordinary differential
equation as contained in above theorems (4.1.1 – 4.1.3), the
solution of both models with positive initial conditions exists
and are unique. Here, we can see for the first differential
equation in both models, that it has a solution, which is also
unique, i.e S = −αSI + γR with positive initial conditions.
In this case, both the function Ft, S! = −αSI + γR and
its partial derivative
?
?e Ft, S! = −αI are defined and
continuous at all points (t, S). The theorem guarantees that a
solution to the ODE exists in some open interval centered at
t3 and that this solution is unique in some (possibly smaller)
interval centered at t3 .
NB: This is also true for the remaining equations in both
models.