MATH0093 Finance and Numerics 2021
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MATH0093 Finance and Numerics
Main Summer Assessment
2021
1. Consider a perpetual American call option V (S) ; which satisÖes the problem
72 S2 + (r 一 D) S 一 rV = 0; 0 < S < S* ;
limV (S) 二 0; V (S* ) = S* 一 E; dV (S* ) = 1:
(1.1)
(1.2)
S 2 0 is the spot price, E > 0 is the strike, S* > 0 is the optimal exercise boundary, 7 > 0 is the constant volatility, r > 0 is the constant interest rate and D > 0 is the dividend yield.
a. Show that for 0 ≤ S ≤ S* requires a solution given by V (S) = ASa+
where A is an arbitrary constant and
a+ = .(╱) ╱ 1 一 (r 一 D)、+ / ╱1 一 (r 一 D)、2 + .(、) :
[10 Marks]
b. Using appropriate conditions in (1:2) calculate the option price V (S) and the optimal exercise boundary S* : [12 Marks]
c. Give a Önancial interpretation of the case when D = 0: [3 Marks]
2. a. A share currently trades at £60. A European call option with strike price £ 58 and expiry in three months trades at £3. The risk-free three month discount rate (continuously compounded and annualised) is 5%. A European put is o§ered on the market, with strike price £ 58 and expiry in three months, for £ 1.50. Do any arbitrage opportunities exist? If there is a possible arbitrage, construct a portfolio that will take advantage of it. [3 Marks]
b. Consider a put option to sell 200 shares of company PKZ for $25 per share. How should the option contract be adjusted after a three-for-one stock split? How is the option price a§ected? [3 Marks]
c. In the context of classifying exotic options, discuss with examples
i. strong path dependence. [3 Marks]
ii. embedded decisions. [3 Marks]
iii. order of an option. [3 Marks]
d. An asset S follows the lognormal random walk
dS = μSdt + 7SdW
and we wish to value a derivative that pays o§ at expiry T an amount which is a function of the path taken by the asset between time zero and expiry.
Assuming that an option value V thus depends on S; t and a quantity
t
I = f (S;r) dr
0
where f is a speciÖed function and r the risk free interest rate, V (S;I;t) satisÖes the pricing equation
+ 72 S2 + f (S;t) + rS 一 rV = 0:
For an arithmetic strike Asian call option the payo§ at time T is
max ╱S 一 0 T S (r)dr;0、
and for a put option the payo§ is
max ╱ 0 T S (r)dr 一 S;0、:
Write down the corresponding partial di§erential equation for this call option VC (S;I;t) and put option VP (S;I;t) ; and hence verify that
VC (S;I;t) 一 VP (S;I;t) = S ╱ 1 一 /1 一 e-r(T -t)、、
t
一 e-r(T -t) S (r) dr
0
[10 Marks]
3. This is a short essay question on the Implicit Finite Di§erence Method
You are required to price a European call option on a dividend paying stock, numerically, using a forward marching scheme. The interest rate is a function of time, the dividend depends on the stock price and time. Your outline should summarise the following
● PDE, boundary and payo§ conditions [3 Marks]
● Suitable discretisation of the mathematical problem [9 Marks]
● Discussion of an indirect method to solve the resulting matrix inversion problem. [13 Marks]
4. This question is on stochastic interest rates
a. Suppose the spot interest rate r, which is a function of time t; satisÖes the stochastic di§erential equation
dr = dWt :
dWt is an increment in a Brownian motion. Using this model for the spot rate, by hedging one bond V (r;t;T) of maturity T, with another of a di§erent maturity, outline a derivation of the bond pricing equation
@V 1 @2 V @V
@t 2 @r2 @r
where A = A(r;t) is an arbitrary function. [3 Marks]
b. By considering an unhedged bond and the risk free return, explain how and why A arises in (4:1). [3 Marks]
c. Assume that A is a function of t only, i.e. A = A(t) and a zero coupon bond is to be priced by solving (4:1) : Find a solution of the form
V (r;T;T) = exp(A(t;T) + rB (t;T)) ;
with redemption value
V (r;T;T) = 1
where both A(t;T) and B (t;T) should be given. [10 Marks]
d. Suppose at a Öxed time t* the spot rate is r* , and on this date, bond prices in the markets are given for a continuous range of ma- turities T; so that VM (r* ;t* ;T) is a known funtion of T: Calculate the precise form of A(t); where A is a funtion of t only. [9 Marks]
2022-04-26