Unified Pricing of Asian Options

A simple and numerically stable 2-term partial differential equation characterizing the price of any type of arithmetically averaged Asian option is given. The approach includes both continuously and discretely sampled options and it is easily extended to handle continuous or discrete dividend yields. In contrast to present methods, this approach does not require to implement jump conditions for sampling or dividend days. Asian options are securities with payoff which depends on the average of the underlying stock price over certain time interval. Since no general analytical solution for the price of the Asian option is known, a variety of techniques have been developed to analyze arithmetic average Asian options. There is enormous literature devoted to study of this option. A number of approximations that produce closed form expressions have appeared, most recently in Thompson (1999), who provides tight analytical bounds for the Asian option price. Geman and Yor (1993) computed the Laplace transform of the price of continuously sampled Asian option, but numerical inversion remains problematic for low volatility and/or short maturity cases as shown by Fu, Madan and Wang (1998). Very recently, Linetsky (2002) has derived new integral formula for the price of continuously sampled Asian option, which is again slowly convergent for low volatility cases. Monte Carlo simulation works well, but it can be computationally expensive without the enhancement of variance reduction techniques and one must account for the inherent discretization bias resulting from the approximation of continuous time processes through discrete sampling as shown by Broadie, Glasserman and Kou (1999). In general, the price of an Asian option can be found by solving a partial differential equation (PDE) in two space dimensions (see Ingersoll (1987)), which is prone to oscillatory solutions. Ingersoll also observed that the two-dimensional PDE for a floating strike Asian option can be reduced to a one-dimensional PDE. Rogers and Shi (1995) have formulated a one-dimensional PDE that can model both floating and fixed strike Asian options. However this one-dimensional PDE is difficult to solve numerically since the diffusion term is very small for values of interest on the finite difference grid. There are several articles which try to improve the numerical performance of this PDE type. Andreasen (1998) applied Rogers and Shi’s reduction to discretely sampled Asian option. ∗I would like to thank Mark Broadie, Peter Carr, Georgios Dalakouras, Paul Glasserman, David Heath, Vicky Henderson, Ioannis Karatzas, Takeaki Kariya, Steven Kou, Dmitry Kramkov, Vadim Linetsky, Ryozo Miura, Yoshio Miyahara, Marek Musiela, Roy Nicolaides, Dmitry Pugachevsky, Stan Pliska, Eric Reiner, William Shaw, Steven Shreve, Jürgen Topper, Tadashi Uratani, Mingxin Xu, participants of seminars at Carnegie Mellon University, Columbia University, Kyoto University, University of Michigan, Hosei University, North Carolina State University, JAFEE conference 2001 in Tokyo and Risk Waters Math Week 2001 in New York.