Bayes rule¶
To derive the bayes rule first we start with joint and conditional distribution.
p(A|B) is the probability that event A will happen given that we know that B has happended.
p(A|B)=p(A,B)p(B)
P(A,B) this tells us the probability that booth A and B have happend.
p(B) is a normalization constant. (But it has happend)
Now we can express this the other way:
P(B|A)=p(B,A)p(A)
The joint distribution is simetric:
p(A,B)=p(B,A)
Now we can rearange the terms:
p(A,B)=p(B,A)p(A|B)p(B)=p(B|A)p(A)p(A|B)=p(B|A)p(A)p(B)
And we have drived the bayes rule.