Formulation of the model
Let the total population size at time t be denoted by N(t). We divide the
population N(t) into
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: