- #1
lyuriedin
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Homework Statement
We are given a belief network such that the overall joint probability after accounting for conditional independence is:
P(a,b,c,d,e) = P(a)P(c|a,b)P(d|b)P(e|d,b)
The values provided are:
P(a = false) = .02
P(b = false) = .95
P(c= false|a=true, b=true) = .97
P(c= false|a=true, b=false) =.04
P(c= false|a=false,b= true) = .99
P(c= false|a=false,b=true) = .1
P(d= false|b=true) = .03
P(d= false|b=true) = .98
P(e=false|d=true, b= true) = .92
P(e=false|d=true, b= false) = .01
P(e=false|d=false, b= true) = 1
P(e= false|d= false, b= false) = 1
The problem is to find
P (b=true|e=false)
Homework Equations
I know that
P(b|d) = P(b,d)/P(d)
and so I need to sum out until I get the marginals I need
The Attempt at a Solution
i.e. P(b,d)=Sum_over_a(Sum_over_c(Sum_over_e(P(a,b,c,d,e)))
= Sum_over_a(Sum_over_c(Sum_over_e(P(a)P(c|a,b)P(d|b)P(e|d,b)))
But I can't work out how to do this.