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CSE 3504: Probabilistic Analysis of Computer Systems. Topics covered: Multiple random variables Transform methods (Sec. 4.1-4.2, 4.5.7). Sum of random variables: Expectation. Expectation of a sum of two random variables: Expectation of a sum of n random variables:
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CSE 3504: Probabilistic Analysis of Computer Systems Topics covered: Multiple random variables Transform methods (Sec. 4.1-4.2, 4.5.7)
Sum of random variables: Expectation • Expectation of a sum of two random variables: • Expectation of a sum of n random variables: • Special case: All the random variables have the same mean
Sum of random variables: Expectation • Alternate expression for variance:
Sum of random variables: Expectation • Example: Variance of the number of heads in a sequence of three coin tosses
Sum of random variables: Variance • Exponential random variable:
Moment generating function • Definition:
Moment generating function (contd..) • Laplace-Stilje’s transform:
Moment generating function (contd..) • Probability Generating Function:
Moment generating function (contd..) • How to use these functions:
Moment generating function (contd..) • Laplace-Stilje’s transform of the exponential distribution:
Moment generating function (contd..) • Convolution theorem:
Moment generating function (contd..) • Sum of exponential random variables (Erlang distribution):