MATH3075: FINANCIAL DERIVATIVES Semester 2, 2021
Hello, dear friend, you can consult us at any time if you have any questions, add WeChat: daixieit
Semester 2, 2021
MATH3075: FINANCIAL DERIVATIVES (Mainstream)
1. [20 marks] Single-period market model
Consider a single-period market model M = (B< s) on the space Ω = (u1 < u2 < u3 }. We assume that the savings account B equals B0 = 1< B1 = 1 + r = 2 and the stock price s is given by s0 = 11 and s1 = (s1 (u1 )< s1 (u2 )< s1 (u3 )) = (24< 20< 16). The real-world probability P is such that P(ui ) = pi > 0 for i = 1< 2< 3.
(a) Find the class M of all martingale measures for the model M and check if the market model M is arbitrage-free and complete.
(b) Show that the contingent claim X = (8< 6< 4) is attainable and compute its arbitrage price n0 (X) using two methods:
– the replicating strategy for X ,
– the risk-neutral valuation formula.
(c) Consider the contingent claim y = (4< 2< -3).
– Find the range of arbitrage prices for y in M. Is the claim y attainable in M?
– Find the minimal initial endowment z for which there exists a portfolio (z< .) with v0 (z< .) = z and such that the inequality v1 (z< .)(ui ) > y (ui ) is satisfied for i = 1< 2< 3.
(d) Consider the extended market = (B< s1 < s2 ) where s1 = s and s2 is an additional risky asset given by: s1(2) = y = (4< 2< -3) and s0(2) = 1,35.
– Find a unique martingale measure for the extended market = (B< s1 < s2 ).
– Compute the price of the claim z = (-2< 5< 3) in the extended market = (B< s1 < s2 ). Is the claim z attainable in ?
2. [20 marks] CRR model: European contingent claim
Consider the CRR model with s0 = 100< u = 1,4< d = 1,1 and r = 0,25. Let X be a European contingent claim with maturity date T = 2 and the payoff X given by
X = (s2 - s1 + 4)1{s2 一s1 >15} =
(a) Show explicitly that the contingent claim X is path-dependent and compute the arbitrage price process for X using the relationship, which holds for
t = 0< 1,
nt (X) = Bt E ╱ │ rt 、
where is a unique martingale measure for the CRR model.
(b) Find the replicating strategy . for the claim X and verify if the equality vt (.) = nt (X) is satisfied for t = 0< 1< 2.
(c) Find a unique probability measure on (Ω < r2 ) such that the process Bs一1
n0 (y) = s0 E ╱ 、,
(d) Let y and z be two European contingent claims with maturity T in the general CRR model with any number T of periods. Assume that the equality nU (y) = nU (z) holds for some date U such that 0 ← U ← T. Does this assumption imply that nt (y) = nt (z) for every U ← t s T?
3. [20 marks] CRR model: American contingent claim
Consider the CRR model with the horizon date T = 2 and s0 = 8< s1(u) = 11< s1(d) = 7, We assume that the interest rate r = 0. Let Xa be an American claim with the maturity date T = 2 and the reward process (gt < t = 0< 1< 2) where g0 = g1 = 12 and the random payoff g2 equals g2 = (14< 10< 10< 18), that is,
g2 (s1(u)< s2(uu)) = 14< g2 (s1(u)< s2(ud)) = g2 (s1(d)< s2(du)) = 10< g2 (s1(d)< s2(dd)) = 18,
(a) Find the unique martingale measure on (Ω < r2 ) and compute the price process Ca for this option using the recursive relationship, which holds for
t = 0< 1,
nt (Xa ) = max {gt < Bt E ╱ │rt 、}
with terminal condition nT (Xa ) = g2 . Find the rational exercise time r0(*) of this claim by its holder.
(b) Find the replicating strategy . for the issuer of the American claim Xa up to the rational exercise time r0(*) and verify if the equality vt (.) = nt (Xa ) holds up to time r0(*) .
(c) Find the early exercise premium for the American claim Xa .
(d) Determine whether the arbitrage price n(Xa ) is a supermartingale or a submartingale under with respect to the filtration F. Find a probabil- ity measure Q on (Ω < r2 ) under which the process n(Xa ) is a martingale with respect to the filtration F.
4. [20 marks] Black-Scholes model: European contingent claim
We assume that the stock price s is governed under the martingale measure by the Black-Scholes stochastic differential equation
dst = st ╱r dt + a dwt、< s0 > 0<
where a > 0 is the stock price volatility and r is the instantaneous interest rate. Consider a European claim X with maturity T and payoff X = lK - sT l - LsT where K > 0 and L > 0 are real numbers.
(a) Show that the payoff X satisfies X = PT (K) + CT (K) - LsT . We henceforth assume that the strike K = s0 erT . Using the Black-Scholes pricing formulae for call and put options, find an explicit expression for the arbitrage price n0 (X).
(b) Compute the hedge ratio at time 0 for the claim X . Examine the sign of the hedge ratio when L = 0.
(c) Find a unique value of L such that n0 (X) = 0 and show that it satisfies 0 ← L ← 2. Compute the limits lim T →0 n0 (X) and limg →& n0 (X).
(d) Assume that r = 0. Show that the process s2 is a submartingale under , that is, the inequality E ╱ss(2) l rt ) > st(2) holds for all dates 0 s t s s.
2022-10-24