The SIR model formula text in examples/deterministic/ex01a-SIR.ipynb has a typo in the dI/dt equation. It was defined there:
$$
\lambda(t) = \frac{\beta I}{N}
$$
and then:
$$
\dot I &= \lambda(t)I - \gamma I \
$$
It should be:
$$
\dot I &= \lambda(t) - \gamma I \
$$
\lambda(t) already has I as a multiplicative factor
The SIR model formula text in examples/deterministic/ex01a-SIR.ipynb has a typo in the dI/dt equation. It was defined there: $$ \lambda(t) = \frac{\beta I}{N} $$ and then: $$ \dot I &= \lambda(t)I - \gamma I \ $$
It should be: $$ \dot I &= \lambda(t) - \gamma I \ $$
\lambda(t) already has I as a multiplicative factor