Written Assignment 5

Friday 11/30/2012, 11:59pm.

The assignment should be submitted via Blackboard.

Questions 1-6 refer to the Bayesian network in Figure 1. Questions 7 and 8 refer to the Bayesian network in Figure 2.




Figure 1: A Bayesian network graph establishing relations between various car problems and their causes.

Problem 1

10 points.

On the network shown in Figure 1, consider the event E = "battery age is less than three years". Let A = P(E | "battery dead"=true AND "no oil"=true) and B = P(E | "battery dead"=true AND "no oil"=false). Which of the following three cases can possibly be true: A > B, A = B, or A < B? Why?


Problem 2

10 points.

On the network shown in Figure 1, consider again the event E = "battery age is less than three years". Let A = P(E | "battery dead"=true AND "no oil"=true) and B = P(E | "battery dead"=true AND "starter broken"=true). Which of the following three cases can possibly be true: A > B, A = B, or A < B? Why?


Problem 3

10 points.

The "alternator broken" event and the "fanbelt broken" event are both causes of the "no charging event." Let A = P("alternator broken"=true | "no charging"=true) and B = P("alternator broken"=true | "no charging"=true AND "fanbelt broken"=true). Which of the following three cases do you expect to be true: A > B, A = B, or A < B? Why?


Problem 4

10 points.

On the network shown in Figure 1, the "no gas" event is a cause of the "car won't start" event. Let A = P("no gas"=true) and B = P("no gas"=true | "car won't start"=true). Which of the following three cases do you expect to be true: A > B, A = B, or A < B? Why?


Problem 5

20 points.

On the network shown in Figure 1, suppose that:

What is P("no charging"=false)? How is it derived?


Problem 6

20 points.

Suppose that:

What is P("battery age" <= 3 years | "battery dead"=true)? How is it derived?




Figure 2: A Bayesian network establishing relations between events on the burglary-earthquake-alarm domain, together with complete specifications of all probability distributions.

Problem 7

10 points.

On the network shown in Figure 2, what is the probability of the following event: burglary=false AND earthquake=true AND alarm=false AND JohnCalls=true AND MaryCalls=false.


Problem 8

10 points.

On the network shown in Figure 2, what is the probability of the following event: earthquake=true AND alarm=false AND JohnCalls=true AND MaryCalls=false.