Solution
= Solution
The <ordinary differential equations> are
$$
\dot S=-\beta SI/N,
\qquad
\dot I=\beta SI/N,
\qquad
\beta>0,\qquad S,I\geq0.
$$
The <conservation of population> identity $S+I=N$ follows by adding the equations.
= Solution
The <ordinary differential equations> are
$$
\dot S=-\beta SI/N,
\qquad
\dot I=\beta SI/N,
\qquad
\beta>0,\qquad S,I\geq0.
$$
The <conservation of population> identity $S+I=N$ follows by adding the equations.