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This document provides a comprehensive overview of key concepts in stochastic calculus as introduced in Chapter 7 of Paul Wilmott's "Introduces Quantitative Finance." It covers essential topics such as coin tossing, the Markov property, martingale property, quadratic variation, Brownian motion, and stochastic differential equations. Additionally, it explores models of financial dynamics including geometric Brownian motion, mean-reverting processes, and popular methods for simulating yields. These concepts are foundational for understanding financial modeling and analysis in quantitative finance. ###
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Financial Engineering Zvi Wiener mswiener@mscc.huji.ac.il 02-588-3049 http://pluto.mscc.huji.ac.il/~mswiener/zvi.html
Elementary Stochastic Calculus Following Paul Wilmott, Introduces Quantitative Finance Chapter 7 http://pluto.mscc.huji.ac.il/~mswiener/zvi.html
Coin Tossing • Ri = -1 or 1 with probability 50% • E[Ri] = 0 • E[Ri2] = 1 • E[Ri Rj] = 0 • Define FE-Wilmott-IntroQF Ch7
Coin Tossing FE-Wilmott-IntroQF Ch7
Markov Property • No memory except of the current state. • Transition matrix defines the whole dynamic. FE-Wilmott-IntroQF Ch7
The Martingale Property • Some technical conditions are required as well. FE-Wilmott-IntroQF Ch7
Quadratic Variation • For example of a fair coin toss it is = i FE-Wilmott-IntroQF Ch7
Brownian Motion FE-Wilmott-IntroQF Ch7
Brownian Motion • Finiteness – does not diverge • Continuity • Markov • Martingale • Quadratic variation is t • Normality: X(ti) – X(ti-1) ~ N(0, ti-ti-1) FE-Wilmott-IntroQF Ch7
Stochastic Integration FE-Wilmott-IntroQF Ch7
Stochastic Differential Equations dX has 0 mean and standard deviation FE-Wilmott-IntroQF Ch7
Stochastic Differential Equations FE-Wilmott-IntroQF Ch7
Simulating Markov Process • The Wiener process The Generalized Wiener process The Ito process FE-Wilmott-IntroQF Ch7
value time FE-Wilmott-IntroQF Ch7
Ito’s Lemma • dt dX • dt 0 0 • dX 0 dt FE-Wilmott-IntroQF Ch7
Arithmetic Brownian Motion • At time 0 we know that S(t) is distributed normally with mean S(0)+t and variance 2t. FE-Wilmott-IntroQF Ch7
S time Arithmetic BMdS = dt + dX FE-Wilmott-IntroQF Ch7
The Geometric Brownian Motion Used for stock prices, exchange rates. is the expected price appreciation: = total - q. S follows a lognormal distribution. FE-Wilmott-IntroQF Ch7
The Geometric Brownian Motion FE-Wilmott-IntroQF Ch7
The Geometric Brownian Motion FE-Wilmott-IntroQF Ch7
S time Geometric BMdS = Sdt + SdX FE-Wilmott-IntroQF Ch7
The Geometric Brownian Motion FE-Wilmott-IntroQF Ch7
Mean-Reverting Processes FE-Wilmott-IntroQF Ch7
Mean-Reverting Processes FE-Wilmott-IntroQF Ch7
Speed of mean reversion Long term mean Simulating Yields • GBM processes are widely used for stock prices and currencies (not interest rates). A typical model of interest rates dynamics: FE-Wilmott-IntroQF Ch7
Simulating Yields • = 0 - Vasicek model, changes are normally distr. • = 1 - lognormal model, RiskMetrics. • = 0.5 - Cox, Ingersoll, Ross model (CIR). FE-Wilmott-IntroQF Ch7
Mean Reverting ProcessdS = (-S)dt + SdX S time FE-Wilmott-IntroQF Ch7
Other models • Ho-Lee term-structure model • HJM (Heath, Jarrow, Morton) is based on forward rates - no-arbitrage type. • Hull-White model: FE-Wilmott-IntroQF Ch7
Home Assignment • Read chapter 7 in Wilmott. • Follow Excel files coming with the book. FE-Wilmott-IntroQF Ch7