ST330 2022 Mock Coursework
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ST330 2022 Mock Coursework
1. Consider a CRR model with stock price S with value at time 0 given by S0 =
40. Over a single period, S can either move up to 50 or down to 30, with equal probability. The (continuously compounded interest rate is 10% in each period.
(a) Use R to compute the risk neutral probability of an upward move. [5 marks]
(b) In the single period case, compute the value at time zero of a European call option with maturity T = 1 and strike price 45. [10 marks]
(c) Consider now the six period case, where in each step the upward factor is 5/4 and downward factor is 3/4. You may use here the following function which generates the values of the stock at any time between t = 0 and t = 6.
Stocktree = matrix(0, nrow=7, ncol=7)
u = 5/4
d = 3/4
for (i in 1:(7)) {
for (j in 1:i) {
Stocktree[i,j] = 40 * u^(j-1) * d^((i-1)- (j-1)) }
}
Stocktree
i. Use the Stocktree to find the median of S6 . [5 marks]
ii. Compute the value at any node of a European call option on S in this six-period model, with maturity T = 6 and strike price 45. [20 marks]
2. Let S0 = 10, T = 2, µ = 1 and σ 2 = 2 i.e. one risky asset which has value at time
T given by
ST = S0 e(µ −σ 2 /2)T+σBT
where B denotes standard Brownian motion. Recall that BT follows a normal
distribution with mean 0 and variance T.
(a) With the values µ, σ, T, S0 as defined use R to compute the mean m of X := log(ST ) given by
m <- log(S_0)+(mu-sigma^2/2)T . [5 marks]
(b) Use the vector
x <- seq(1,7,by=0 .1)
and the dnorm command to plot the density dens of log ST . Note that dnorm takes generates the values of the corresponding normal distribution based on an input vector. [10 marks]
(c) Find the 10% quantile of log(ST ). You may use the qnorm command for this. [5 marks]
(d) Highlight in red on the plot the area under the density between the 25% and 75% quantiles. This can be done by following the plot command by
polygon(c( A,x[i],B), c(0,dens[i],0), col="red") where A and B are to be determined. [10 marks]
(e) Assume that for the risk free rate r we have r = 1 and consider European put option on S with strike price K = 11 and T = 2. You may use without proof any result derived in the lectures.
i. Use R to find the value at time 0 of a European put option on S with strike K = 11 and T = 2. [10 marks]
ii. Now let S0 be general and plot the value at time 0 of this European put option as a function of S0 . [20 marks]
2023-05-12