| Perplexity of fixed-length models | |
| [[open-in-colab]] | |
| Perplexity (PPL) is one of the most common metrics for evaluating language models. Before diving in, we should note | |
| that the metric applies specifically to classical language models (sometimes called autoregressive or causal language | |
| models) and is not well defined for masked language models like BERT (see summary of the models). | |
| Perplexity is defined as the exponentiated average negative log-likelihood of a sequence. |