Formulation of the model
Let the total population size at time t be denoted by N(t).
We divide the population N(t) into fi
ve subclasses,
potential smokers (non-smoker) P(t),
occasional (Light) smokers L(t),
heavy smokers S(t),
smokers who temporary quit smoking Qt(t)
and smokers who permanently quit smoking Qp(t)
such that N(t) = P(t) + L(t) + S(t) +Qt(t) +Qp(t):In [1] we studied the dynamics
of smoking by the following four non-linear di¤erential equations: