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Let X and Y be independent exponential random variables with mean 1.

(a) Explain how we could use simulation to estimate E[eXY].

(b) Show how to improve the estimation approach in part (a) by using a control variate.

Short Answer

Expert verified

(a) Estimator M=1n∑i=1neXiYi
(b) Redefine estimator Mˆ=1n∑i=1neXiYi+cXiYi−1and it is defined below.

Step by step solution

01

Part (a) Step 1: Given Information

We need to explain the simulation to estimateEeXY.

02

Part (a) Step 2: Simplify

Considering to define X1,…,Xn~Xand Y1,…,Yn~Y.

Now, consider the statistic

M=1ni=1neXiYi

It is simple to show that EM=EeXYso we have provided a good method of estimation of the mean.

03

Part (b) Step 1: Given Information

We need to give the solution to improve the estimation approach in part (a) by using a control variate.

04

Part (b) Step 2: Simplify

Consider

Mˆ=1ni=1neXiYi+cXiYi−1

Serve that it also holds

EMˆ=1ni=1nEeXiYi+cXiYi−1=EeXY

as we haveEcXiYi−1=0. Let's minimize the variance. We have that

VarMˆ=1n2i=1nVareXiYi+cXiYi−1

Keeping that

VareXiYi+cXiYi−1=VareXiYi+c2VarXiYi−1+cCoveXiYi,XiYi−1

So, we have seen that the Variance is minimized when

c=−CoveXiYi,XiYi−1VarXiYi−1

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