LAGRANGE MULTIPLIER APPROACH WITH OPTIMIZED FINITE DIFFERENCE STENCILS FOR PRICING AMERICAN OPTIONS UNDER STOCHASTIC VOLATILITY

The deterministic numerical valuation of American options under Heston's stochastic volatility model is considered. The prices are given by a linear complementarity problem with a two-dimensional parabolic partial differential operator. A new truncation of the domain is described for small asset values, while for large asset values and variance a standard truncation is used. The finite difference discretization is constructed by numerically solving a quadratic optimization problem aiming to minimize the truncation error at each grid point. A Lagrange approach is used to treat the linear complementarity problems. Numerical examples demonstrate the accuracy and effectiveness of the proposed approach.