1 Perplexity
公式如下所示:
P P L ( S ) = P ( w 1 w 2 . . . w N ) − 1 N l o g P P L ( S ) = − l o g P ( w 1 w 2 . . . w N ) N = − ∑ i = 1 N l o g P ( w i ∣ w 1 . . . w i − 1 ) N PPL(S)=P(w_1w_2...w_N)^{-\frac{1}{N}}\\ logPPL(S)=\frac{-logP(w_1w_2...w_N)}{N}=\frac{-\sum_{i=1}^{N}logP(w_i|w_1...w_{i-1})}{N} PPL(S)=P(w1w2...wN)−N1logPPL(S)=N−logP(w