Stochastic volatility models form a rich class of models which, in particular, generate
the observed skews of implied volatilities [see for instance Fouque et al. (2000)]. In
general, unlike in the Black-Scholes model, there is no explicit option pricing formula,
one exception being the Heston model (Heston 1993) for which European options are
given semi-explicitly, up to an inverse Fourier transform.