Hello, dear friend, you can consult us at any time if you have any questions, add WeChat: THEend8_
ASSIGNMENT
MATH3075 Financial Derivatives (Mainstream) 1. [10 marks] CRR model: American put option. Consider the CRR model with T = 2 and S0 = 100, Su1 = 120, Sd1 = 90. Assume that the interest rate r = 0. Consider an American put option with reward process g(St, t) = (Lt − St)+ and variable strike price L0 = 105, L1 = 116, L2 = 111. (a) Find parameters u, d, the stock price at time T = 2, and a martingale measure P˜ on (Ω,F2). (b) Compute the price process P a of this option using the recursive relationship P at = max { (Lt − St)+, (1 + r)−1 ( p˜P aut+1 + (1− p˜)P adt+1 )} with the terminal condition P a2 = (L2 − S2)+. (c) Find the holder’s rational exercise time τ ∗0 . (d) Find the replicating strategy for the option up to the exercise time τ ∗0 . (e) Check whether the arbitrage price process (P at ; t = 0, 1, 2) is a martingale or a supermartingale under P˜ with respect to the filtration F. 2. [10marks] Black-Scholesmodel: European claim. We place ourselves within the setup of the Black-Scholes market modelM = (B, S) with a unique martingale measure P˜. Consider a European contingent claim Y with maturity T and the following payoff Y = γST −max (ST , L) where L = erTS0 and γ < 0 is a real number. We take for granted the Black-Scholes pricing formulae for the call and put options. (a) Sketch the profile of the payoff Y as a function of the stock price ST at time T and show that Y admits the representation Y = γST −CT (L)−L where CT (L) denotes the payoff at time T of the European call option with strike L. (b) Find an explicit expression for the arbitrage price pit(Y ) at time 0 ≤ t < T in terms of Ft := ertS0, St and S0. Then compute the price pi0(Y ) in terms of S0 and use the equality N(x)−N(−x) = 2N(x)− 1 to simplify your result. (c) Compute and describe the hedging strategy at time 0 for the claim Y . (d) Find the limits limσ→0 pi0(Y ) and limσ→∞ pi0(Y ). (e) Explain why the price pi0(Y ) is negative when γ = 1 by analysing the payoff Y .