Chapter 11: Problem 2
Give a method for simulating a negative binomial random variable.
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Chapter 11: Problem 2
Give a method for simulating a negative binomial random variable.
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Let \((X, Y)\) be uniformly distributed in a circle of radius \(r\) about the origin. That is, their joint density is given by $$ f(x, y)=\frac{1}{\pi r^{2}}, \quad 0 \leqslant x^{2}+y^{2} \leqslant r^{2} $$ Let \(R=\sqrt{X^{2}+Y^{2}}\) and \(\theta=\arctan Y / X\) denote their polar coordinates. Show that \(R\) and \(\theta\) are independent with \(\theta\) being uniform on \((0,2 \pi)\) and \(P\\{R
Give an algorithm for simulating a random variable having density function
$$
f(x)=30\left(x^{2}-2 x^{3}+x^{4}\right), \quad 0
In Example \(11.4\) we simulated the absolute value of a standard normal by using the Von Neumann rejection procedure on exponential random variables with rate \(1 .\) This raises the question of whether we could obtain a more efficient algorithm by using a different exponential density-that is, we could use the density \(g(x)=\lambda e^{-\lambda x}\). Show that the mean number of iterations needed in the rejection scheme is minimized when \(\lambda=1\).
Consider the following procedure for randomly choosing a subset of size \(k\)
from the numbers \(1,2, \ldots, n:\) Fix \(p\) and generate the first \(n\) time
units of a renewal process whose interarrival distribution is geometric with
mean \(1 / p-\) that is, \(P\\{\) interarrival time \(=k\\}=p(1-p)^{k-1}, k=1,2,
\ldots .\) Suppose events occur at times \(i_{1}
Consider the technique of simulating a gamma \((n, \lambda)\) random variable by using the rejection method with \(g\) being an exponential density with rate \(\lambda / n\). (a) Show that the average number of iterations of the algorithm needed to generate a gamma is \(n^{n} e^{1-n} /(n-1) !\). (b) Use Stirling's approximation to show that for large \(n\) the answer to part (a) is approximately equal to \(e[(n-1) /(2 \pi)]^{1 / 2}\). (c) Show that the procedure is equivalent to the following: Step 1: Generate \(Y_{1}\) and \(Y_{2}\), independent exponentials with rate 1 . Step 2: \(\quad\) If \(Y_{1}<(n-1)\left[Y_{2}-\log \left(Y_{2}\right)-1\right]\), return to step 1 . Step 3: \(\quad\) Set \(X=n Y_{2} / \lambda\) (d) Explain how to obtain an independent exponential along with a gamma from the preceding algorithm.
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