Language Modelling

Perplexity Definition 1 Given a sequence $X = x_1, x_2, \dots, x_T$ of words and a language model $p$, the perplexity of the sequence can is defined as follows: $$ \text{PPL}(X) = p(x_1, x_2, \dots, x_T)^{-\frac{1}{T}} $$