Generic algorithm for probability any propositional formula

  • Thread starter Aldebaran2
  • Start date
  • #1

Main Question or Discussion Point

Ciao all,

Is there a generic algorithm to compile the probability P(A)
of any propositional formula A (provided that we have only the probability of each atoms constituting A)?

For example, we have that A= a1 and not (a2 and a3 and ( not a4 and not a5 and not a6 ..) , or any other complicated formula.
The an are independant here!!!!

I know pr(a1), pr(a2)... and so on...

Is there an algorithm to compute pr(a1 and not (a2 and a3 and ( not a4 and not a5 and not a6 ..) ) ?????
 

Answers and Replies

  • #2
980
2
Just repeatedly apply Bayes' rule. But you will have difficulty usually coming up with numbers for all of the required terms.
 
  • #3
Applying Bayes.

Thank you for the advice!! I shall try it.

What did you exactly mean by:

"you will have difficulty usually coming up with numbers for all of the required terms"


???
 
  • #4
980
2
Essentially you'll need all the cross probabilities -- all the and's and or's of the all the possible pairs of propositions. Usually, these numbers aren't easy to come up with.
 
  • #5
I do not get it.

Could you provide an example?

or do you have a reference where that is well explained ( I am not an expert of Probabiliies)?
 
  • #6
980
2
Any standard probabilities textbook would be a good place to start. My personal favourite is Probability Theory by E.T. Jaynes.
 
  • #7
EnumaElish
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Well, if the a's are independent, that simplifies the problem considerably.
 
  • #8
Ciao EnumaElish,

Do you have an algorithm? eventually a reference to it?
 
  • #9
980
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Ciao EnumaElish,

Do you have an algorithm? eventually a reference to it?
I'm fairly sure nothing beyond a textbook would even bother to spell it out:

given two independent events, A and B, pr(A and B) = pr(A) pr(B), pr(A or B) = pr(A) + pr(B). Generalise in the obvious way for more than 2 events.
 
  • #10
EnumaElish
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Last edited:

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