Evaluating Perplexity on Language Models

What’s Happening

Okay so This article is divided into two parts; they are: • What Is Perplexity and How to Compute It • Evaluate the Perplexity of a Language Model with HellaSwag Dataset Perplexity is a measure of how well a language model predicts a sample of text.

Evaluating Perplexity on Language Models By Adrian Tam on in Training Transformer Models 0 Post A language model is a probability distribution over sequences of tokens. When you train a language model, you want to measure how accurately it predicts human language use. (we’re not making this up)

This is a difficult task, and you need a metric to evaluate the model.

The Details

In this article, you will learn about the perplexity metric. Specifically, you will learn: What is perplexity, and how to compute it How to evaluate the perplexity of a language model with sample data Lets get kicked off.

Evaluating Perplexity on Language Models Photo by Lucas Davis . Overview This article is divided into two parts; they are: What Is Perplexity and How to Compute It Evaluate the Perplexity of a Language Model with HellaSwag Dataset What Is Perplexity and How to Compute It Perplexity is a measure of how well a language model predicts a sample of text.

Why This Matters

It is defined as the inverse of the geometric mean of the probabilities of the tokens in the sample. Mathematically, perplexity is defined as: $$ PPL(x_(1:L)) = \prod_(i=1)^L p(x_i)^(-1/L) = \exp\big(-\frac(1)(L) \sum_(i=1)^L \log p(x_i)\big) $$ Perplexity is a function of a particular sequence of tokens. In practice, it is more convenient to compute perplexity as the mean of the log probabilities, as shown in the formula above.

This adds to the ongoing AI race that’s captivating the tech world.

Key Takeaways

Perplexity is a metric that quantifies how much a language model hesitates about the next token on average.
If the language model is absolutely certain, the perplexity is 1.
If the language model is completely uncertain, then every token in the vocabulary is equally likely; the perplexity is equal to the vocabulary size.
You should not expect perplexity to go beyond this range.