MTH 223 Mathematical risk theory Assignment 1
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MTH 223 Mathematical risk theory
Assignment 1
1. In this course, we often encounter the computation of integrals such as 04 t2 eS#at and 4& t2 e #S at. The following formula can be used to expedite the computation:
& t)eS# at = ) n!x本 eS4 , n = 0, 1, . . . . (1.1)
4 本=0 k!
Also note that the Gamma function is defined by
&
Γ(α) = t尸S1 eS# at, α > 0.
0
(a) Prove (1.1) by induction principle.
(b) Using (1.1) to show Γ(n + 1) = n! for n = 0, 1, . . .. Therefore,
0 4 k!
(c) Consider a loss r.v. X ~ GAM(α, θ) with α = 3 and θ = 2 so that it has a pdf
(x/2)3 eS4←2
f(x) = xΓ(3) , x > 0.
Compute Var(X).
2. Assume a random loss X is subject to a normal distribution with mean µ, standard deviation σ, and pdf
f(x) = exp ┌ - ╱ 、2 ┐ .
Let φ(x) and Φ(x) respectively denote the pdf and the cdf of the standard normal distribution. Show the following
(a) VaR也 (X) = µ + σΦS1 (p);
φ ┌Φ S1 (p),
1 - p .
3. Assume a random loss X has a Pareto distribution with scale parameter θ > 0, shape pa- rameter α > 1, and cdf F (x) = 1 - ╱ 、尸 , x > 0. Find VaR也 (X) and TVaR也 (X) for p e (0, 1).
4. Suppose that the distribution of X is continuous on (x0 , o) where -o < x0 < o (this does not rule out the possibility that Pr(X ← x0 ) > 0 with discrete mass points at or below x0 ). For x > x0 , let f (x) be the pdf, h(x) be the hazard rate function, and e(x) be the mean excess loss function. Demonstrate that
d
and hence E [X|X > x] is nondecreasing in x for x > x0 .
5. Assume that a stock index at the end of one year is X which has a Pareto distribution with cdf
F (x) = 1 - ╱ 、3 , x 圹 0.
The return of a one year guaranteed investment linked to the index is Y = max{X, 100}. Denote the distribution function of the return by F…(y).
(a) Calculate F…(y) for all y e (-o, o).
(b) Calculate the mean of the return.
(c) Calculate the median of the return.
(d) Calculate the variance of the return.
2022-05-09