Open CaesarZZP opened 5 years ago
P(A|B) = P(AB)/P(B) = |A∩B| / |B| ① P(B|A) = P(AB)/P(A) = |A∩B| / |A| ② 由①② P(A|B)P(B) = P(B|A)P(A) P(A|B) = P(B|A)P(A) / P(B) 即 P(Y=1 | X1 X2 X3...Xn) = P(X1 X2 X3...Xn | Y)P(Y) / P(X1 X2 X3 ....Xn) P(Y=0 | X1 X2 X3...Xn) = P(X1 X2 X3...Xn | Y)P(Y) / P(X1 X2 X3 ....Xn)
算P(X1 X2 X3...Xn | Y)时 朴素贝叶斯法对条件概率分布做了条件独立性的假设 P(X1 X2 X3...Xn | Y) = ∏P(X=X1|Y)
Normal heart,kidney,endocrine(内分泌),volume status =>normal urine(尿液) output (p->q ≠ q->p)
(p1 & p2 & p3 & p4) -> q ≡ ~q->(~p1 | ~p2 | ~p3 | ~ p4)
直接猜q的几率很难猜,可是如果知道了px,再来猜q,就好猜一点了 p( q|~p1 ) = x1 ... 看哪个概率最大
贝叶斯定理
朴素贝叶斯算法
P(A|B) = P(AB)/P(B) = |A∩B| / |B| ① P(B|A) = P(AB)/P(A) = |A∩B| / |A| ② 由①② P(A|B)P(B) = P(B|A)P(A) P(A|B) = P(B|A)P(A) / P(B) 即 P(Y=1 | X1 X2 X3...Xn) = P(X1 X2 X3...Xn | Y)P(Y) / P(X1 X2 X3 ....Xn) P(Y=0 | X1 X2 X3...Xn) = P(X1 X2 X3...Xn | Y)P(Y) / P(X1 X2 X3 ....Xn)
朴素所在
算P(X1 X2 X3...Xn | Y)时 朴素贝叶斯法对条件概率分布做了条件独立性的假设 P(X1 X2 X3...Xn | Y) = ∏P(X=X1|Y)