In the special case when the {Y,} are themselves log-normally distributed,
then the distribution of S(r)jS will be log-normal with the variance parameter a
Poisson-distributed random variable. In this form, the posited dynamics are
similar to those used by Press (1967).
Having established the stock price dynamics, I now turn to the dynamics of
the option price. Suppose that the option price, IV, can be written as a twicecontinuously
diffcrentiablc function of the stock price and time: namely,
W(r) = F(S, f). If the stock price follows the dynamics described in (2), then
the option return dynamics can be written in a similar form as