ECON5065 Applied Computational Finance Practice Problems Set 1
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ECON5065
Applied Computational Finance
Practice Problems Set 1
1. Let W(t), t > 0, be a Brownian motion, and let F(t), t > 0, be a ltration for this Brownian motion. Show that W2(t) t is a martingale.
(Hint: For 0 < s < t, write W2(t) as (W(t) W(s))2 + 2W(t)W(s) W2(s).)
2. Let the interest rate r and the volatility > 0 be constant. Let S(t) = S(0)e (r 2)t+W(t)
be a geometric Brownian motion with mean rate of return r, where the initial stock price S(0) is positive. Let K be a, positive constant. Show that, for T > 0,
E[e rT(S(T) K)+] = S(0)N(d+(T,S(0)) Ke rTN(d (T,S(0)),
where
d (T,S(0)) = [log + (r )] ,
and N is the cumulative standard normal distribution function
N(y) = e z2 dz = e z2 dz .
3. Let W be a Brownian motion. Fix m > 0 and ∈ R. For 0 < t < ∞, dene X(t) = t + W(t),m = min{t 0;X(t) = m}.
As usual, we set m = ∞ if X(t) never reaches the level m. Let be a positive number and set
Z(t) = exp (X(t) ( + 2) t) .
(a) Show that Z(t), t 0, is a martingale
(b) Use (a) to conclude that
E [exp (X(t ∧ m) ( + 2)(t ∧ m))] = 1, t 0.
(c) Now suppose 0. Show that for > 0,
E [exp (m ( + 2)m) 1{m<∞}] = 1.
Use this fact to show P(m < ∞) = 1 and to obtain the Laplace transform Eem = em m for all > 0.
2022-02-16