Math 502, Spring 2023, Homework 2
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Math 502, Spring 2023, Homework 2
Problem 1. Let X1 , . . . , Xn be independent random variables with common distribution function F , α
be a number in the open interval (0, 1), q be an α-quantile of F and rn be a positive integer satisfying (rn - nα)/^n - 0. In class we have shown the asymptotic normality result
(1) ^n(X(r们 ) - q)--(勿) Y ~ N ╱0, 、
if F has a positive derivative F\ (q) at q . Suppose now that F (q -) < α < F (q) holds. Verify the convergence
(2) nl P (X(r们 ) = q) = 1
Problem 2. Consider the distribution function F given by
,.0, t < 0,
.
t2 , 0 < t < 1/2,
F (t) = .1/2, 1/2 < t < 1,
3/4, 1 < t < 2,
.
..1 - 1/t2 , 2 < t.
Perform a simulation study to investigate the performance of the order statistics X(r们 ) for the following choices of rn .
(1) rn equals the integer part of n/5. Is the behavior consistent with the asymptotic normality result
(1) mentioned in Problem 1?
(2) rn equals to the integer part of n/3. Is the behavior consistent with the result (2) from Problem 1?
Use sample sizes n = 60, n = 120 and n = 240. Use 1000 repetitions.
Problem 3. A random variable X is said to have a Weibull distribution with shape parameter α and scale parameter β if α and β are positive and X has density
f (x) = exp ╱ - 、1[x > 0].
Give an algorithm for generating such a random variable.
Problem 4. A random variable X is said to have a Pareto distribution with shape parameter α and scale parameter β if α and β are positive and X has density
αβ α
xα+1
Give an algorithm for generating such a random variable.
Problem 5. Give an algorithm that generates random variables X and Y with joint density f (x, y) = 4xy exp(-y2 )1[0 < x < y]
Problem 6. Let f and g be two densities on the real line with respective distribution functions F and G, and let θ be a number in the interval (-1, 1). Define a function p on R2 by
p(x, y) = f (x)g(y)(1 + θ(2F (x) - 1)(2G(y) - 1)), x, y ∈ R.
(1) Show that p is a density.
(2) Let X and Y have joint density p. Find marginal densities of X and Y .
(3) Describe an accept/reject algorithm for generating X and Y with joint density p.
2023-02-01