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Monte Carlo: Option Pricing. Reference: Option Pricing by Simulation, Bernt Arne Ødegaard (http://finance.bi.no/~bernt/gcc_prog/recipes/recipes/node12.html). Introduction. Use Monte Carlo to estimate the price of a Vanilla European option priced by Black Scholes equation.
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Monte Carlo: Option Pricing Reference: Option Pricing by Simulation, Bernt Arne Ødegaard (http://finance.bi.no/~bernt/gcc_prog/recipes/recipes/node12.html)
Introduction • Use Monte Carlo to estimate the price of a Vanilla European option priced by Black Scholes equation. • Already a closed form solution, therefore, no need to simulate, • But, for an illustrative process.
… Introduction • At maturity, a call option is worth: • CT = max (0, ST – X) • At an earlier date t, the option will be the expected present value of this: • Ct = E[PV(max (0, ST – X))]
Risk Neutral Result: Simplify • Decision made by a risk neutral investor • Also modify the expected return of the underlying asset such that it earns the risk free rate. • ct = e-r(T – t)E*[(max (0, ST – X))] • Where E*[.] is a transformation of the original expectation.
Monte Carlo • One way to estimate the value of the call is to simulate a large number of sample values of ST according to the assumed price process, and find the estimated call price as the average of the simulated values. • According the “law of large numbers”, this average will converge to the actual call value, depending on the number of simulations that are performed.
Lognormally distributed randoms • Let x be normally distributed with mean zero and variance one. • If St follows a lognormal distribution, the one-period-later price St+1 is simulated as • St+1=Ste(r-½2)+x
…..Lognormally distributed randoms • Or more generally,
Pricing of European Call Options • ct = e-r(T – t)E*[(max (0, ST – X))] • Note that here one merely needs to simulate the terminal price of the underlying, ST, • the price of ST at time between t and T is not relevant for pricing.
…Pricing of European Call Options • Proceed by simulating lognormally distributed random variables. • Let ST,1, ST,2, …. ST,n denote the n simulated ST values
…Pricing of European Call Options • We estimate E*[max (0, ST – X)] as the average of option payoffs at maturity, discounted at the risk free rate.
Price of the Call ( and r constant) • C=Price of the Call • S=Current Stock Price • T=Time of Expiration • X=Strike Price • r=Risk-free Interest Rate • N()=Cumulative normal distribution function • e=Exponential term (2.7183) • =Volatility
Results: • S = 100; X = 110; r = 0.1; • sigma = 0.4; t = 6 • Exact ct = 53.4636 • Monte Carlo: • # sims: 10 ct = 15.4533 • # sims: 1,000 ct = 54.9804 • # sims: 1,000,000 ct = 53.5126 • # sims: 100,000,000 ct = 53.4593 • # sims: 1,000,000,000 ct = 53.4722