Chapter 4. Supplementary Questions
Question 1. Consider the systematic sample estimator based on the trapezoidal rule: Discuss the bias and variance of this estimator. In the case , how does it compare with other estimators such as crude Monte Carlo and antithetic random numbers requiring n function evaluations. Are there any disadvantages to its use?
- - can not be calculated by the sample variance because ‘s are not independent.
The difference (ARN) is 2.6667e-004, almost 0. Results Actual value is . The difference (SS) is 0.0050. The difference (MC) is 0.0391. The difference (ARN) is 2.6667e-004, almost 0. Disadvantage : careful to calculate the variance of the estimator N Crude MC S. S Antithetic 50 0.3217 0.3283 0.3336 100 0.3865 0.3300
Question 2. For any random variables , , prove that for all x, y.
Proof. Case 1. X and Y are independent. Obvious! Case 2. X and Y are not independent.
Question 4. Suppose we wish to generate the partial sum of independent identically distributed summands, for (a) is generated with having (b) is generated with a student What is the maximum possible correlation we can achieve between and ? What is the minimum correlation?
Theorem 40. (maximum/minimum covariance) Suppose and are both non-decreasing (or both non-increasing) functions. Subject to the constraint that X, Y have cumulative distribution functions , respectively, the covariance is maximized when and and is minimized when and , where U~U[0,1].
Solution Using common random number(CRN), the maximum correlation is obtained and Using antithetic random number(ARN), the minimum correlation is obtained. Let , So, ,
Algorithms (sigma=1, n=10, m=100000) Generate For CRN, x=norminv(u,0,1); For ARN, x=norminv(1-u,0,1); y=tinv(u,5); Compute sums of x and y Compute the covariance matrix Compute Corr(sum(x),sum(y))
Results Maximum of covariance is 3.8376e+004 . Minimum of covariance is -1.5634e+005. Thus, the maximum of correlation is 0.9271 and the minimum of correlation is -0.9928 . When dof=2, maximum = 0.7880 and minimum = -0.5521.