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Latest revision as of 00:52, 10 March 2015

1. (15% of Total)

This question is a set of short-answer questions (no proofs):

(a) (5%)

State the definition of a Probability Space.

Answer

You can see the definition of a Probability Space.

(b) (5%)

State the definition of a random variable; use notation from your answer in part (a).

ECE Ph.D. Qualifying Exam

Communication, Networking, Signal and Image Processing (CS)

Question 1: Probability and Random Processes

August 2003



Answer (74p on Papoulis)

A random variable $ \mathbf{X} $ is a process of assigning a number $ \mathbf{X}\left(\xi\right) $ to every outcome $ \xi $ . The result function must satisfy the following two conditions but is otherwise arbitrary:

1. The set $ \left\{ \mathbf{X}\leq x\right\} $ is an event for every $ x $ .

2. The probabilities of the events $ \left\{ \mathbf{X}=\infty\right\} $ and $ \left\{ \mathbf{X}=-\infty\right\} $ equal 0.

Answer (Intuitive definition)

Given $ \left(\mathcal{S},\mathcal{F},\mathcal{P}\right) $ , a random variable $ \mathbf{X} $ is a mapping from $ \mathcal{S} $ to the real line. $ \mathbf{X}:\mathcal{S}\rightarrow\mathbb{R} $ .

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(c) (5%)

State the Strong Law of Large Numbers.

Answer

You can see the definition of the Strong Law of Large Numbers.

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