上海交通大学：自然语言处理（PPT课件讲稿）Natural Language Processing

Forward Procedure X x x T O T a, (t+1) P(01…O+12x+1=j P(01…O+1|x+1=j)P(x1=j) =P(01O1|x1=j)P(Ou|x1=j)P(x+1=j =P(01…O2x1=j)P(O1|x11=j l+1S 16

( ... , ) ( | ) 16 ( ... | ) ( | ) ( ) ( ... | ) ( ) ( ... , ) 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 P o o x j P o x j P o o x j P o x j P x j P o o x j P x j P o o x j t t t t t t t t t t t t t t = = = = = = = = = = = = + + + + + + + + + + + + o1 ot-1 ot ot+1 oT x1 xt-1 xt xt+1 xT Forward Procedure (t +1)  j

Forward Procedure X x x T O T a, (t+1) =P(01…O+1,x+1=j) P(01O+1|x+1=j)P(x+1=j =P(01…O1|x1=) P(O41|x+1=j t+/ P(01…O12x+1=j)P(O1|x1=) l+1S 17

17 o1 ot-1 ot ot+1 oT x1 xt-1 xt xt+1 xT Forward Procedure (t +1)  j ( ... , ) ( | ) ( ... | ) ( | ) ( ) ( ... | ) ( ) ( ... , ) 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 P o o x j P o x j P o o x j P o x j P x j P o o x j P x j P o o x j t t t t t t t t t t t t t t = = = = = = = = = = = = + + + + + + + + + + + +

Forward Procedure X x x T O T a, (t+1) P( =P(01…O+1 )P(x1=j) 1 =P(01…O2|x1=)P(O1|x1=)P(x1=j) =P(01…O2x1=j)P(O1|x11=j

18 o1 ot-1 ot ot+1 oT x1 xt-1 xt xt+1 xT Forward Procedure (t +1)  j ( ... , ) ( | ) ( ... | ) ( | ) ( ) ( ... | ) ( ) ( ... , ) 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 P o o x j P o x j P o o x j P o x j P x j P o o x j P x j P o o x j t t t t t t t t t t t t t t = = = = = = = = = = = = + + + + + + + + + + + +

Forward Procedure X x x T O T a, (t+1) P( =P(01…Om|x1=)P(x1=) =P(01O1|x1=j)P(Ou|x1=j)P(x+1=j t+/ =P(01…O2x1=j)P(O1|x+1=j)

19 o1 ot-1 ot ot+1 oT x1 xt-1 xt xt+1 xT Forward Procedure (t +1)  j ( ... , ) ( | ) ( ... | ) ( | ) ( ) ( ... | ) ( ) ( ... , ) 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 P o o x j P o x j P o o x j P o x j P x j P o o x j P x j P o o x j t t t t t t t t t t t t t t = = = = = = = = = = = = + + + + + + + + + + + +

Forward Procedure X x x T O T ∑P(a1、O,x=1,x1=)P(O1|x1= i=1..N ∑P(a1、O,x1=川x=1)P(x=)P j 1.N ∑P P(x1=jx1=)P(On1|x1=) +1

 20    = + + + = + + = + + + = + + = = = = = = = = = = = = = = = i N i i j j o t t t t i N t t t t t i N t t t t t i N t t t t t a b P o o x i P x j x i P o x j P o o x j x i P x i P o x j P o o x i x j P o x j 1... 1 1 1 1... 1 1 1 1... 1 1 1 1 1... 1 1 1 ( ) ( ... , ) ( | ) ( | ) ( ... , | ) ( ) ( | ) ( ... , , ) ( | )  o1 ot-1 ot ot+1 oT x1 xt-1 xt xt+1 xT Forward Procedure