20.10 The volatility function The volatility function that leads to the model matching all European option prices Is l(K,m)2cn/O+q(lme+Kr()-)moK K(0'Cmk aK2) Options, Futures, and other Derivatives, 5th edition 2002 by John C. HullOptions, Futures, and Other Derivatives, 5th edition © 2002 by John C. Hull 20.10 The Volatility Function The volatility function that leads to the model matching all European option prices is ( ) ( ) [ ( ) ( )] [ ( , )] 2 2 2 2 2 K c K c t q t c K r t q t c K K t mkt mkt mkt mkt     + + −    =