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An Operator Splitting Method for Pricing<br />

American Options<br />

Samuli Ikonen 1 <strong>and</strong> Jari Toivanen 2<br />

1 Nordea Markets, FI-00020 Nordea, Finl<strong>and</strong> Samuli.Ikonen@nordea.com<br />

2 Department of Mathematical Information Technology, P.O. Box 35 (Agora),<br />

FI-40014 University of Jyväskylä, Finl<strong>and</strong> Jari.Toivanen@mit.jyu.fi<br />

Summary. Pricing American options using partial (integro-)differential equation<br />

based methods leads to linear complementarity problems (LCPs). The numerical<br />

solution of these problems resulting from the Black–Scholes model, Kou’s jumpdiffusion<br />

model, <strong>and</strong> Heston’s stochastic volatility model are considered. The finite<br />

difference discretization is described. The solutions of the discrete LCPs are approximated<br />

using an operator splitting method which separates the linear problem<br />

<strong>and</strong> the early exercise constraint to two fractional steps. The numerical experiments<br />

demonstrate that the prices of options can be computed in a few milliseconds on<br />

aPC.<br />

1 Introduction<br />

Since 1973 Black, Scholes, <strong>and</strong> Merton developed models for pricing options in<br />

[BS73, Mer73] <strong>and</strong>, on the other h<strong>and</strong>, the Chicago Board Options Exchange<br />

started to operate, the trading of options has grown to tremendous scale. Basic<br />

options give either the right to sell (put) or buy (call) the underlying asset<br />

with the strike price. European options can be exercised only at the expiry<br />

time while American options can be exercised anytime before the expiry. The<br />

Black–Scholes partial differential equation (PDE) describes the evolution of<br />

the option price in time for European options. In order to avoid arbitrage<br />

opportunities with an American option, the so-called early exercise constraint<br />

has to be posed on its value. Combining this constraint with the PDE leads to<br />

a linear complementarity problem (LCP). For European options it is generally<br />

possible to derive formulas for their price, but American options usually need<br />

to be priced numerically. This paper considers the solution of these pricing<br />

problems. For the general discussion on these topics, we refer to the books<br />

[AP05, CT04, TR00, Wil98].<br />

The Black–Scholes model [BS73] assumes a constant volatility for all options<br />

with different strike prices <strong>and</strong> expiry times on the same underlying<br />

asset. In practice, this does not hold in the markets. One possibility to make

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