Perplexity

Perplexity 

2020/12/21

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PPL，Transformer 的評估標準之一。

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https://pixabay.com/zh/photos/confused-muddled-illogical-880735/

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likelihood 與 probability 的差異

2021/11/20

「Likelihood：用已知的（實驗）數據作出（影響實驗結果的）參數的函數，藉以求取參數的數值。 Probability：用已知的（影響實驗結果的）參數作出（能夠預測實驗結果的）函數，藉以預測實驗的結果。」

簡單說，先有理論得到數據，是 probability，先取樣得到數據，再建立機率模型，是 likelihood。

https://www.zhihu.com/question/50828855

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「Perplexity is defined as the exponentiated average negative log-likelihood of a sequence. 」

https://huggingface.co/transformers/perplexity.html

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References

# PPL

Gamallo, Pablo, José Ramom Pichel Campos, and Inaki Alegria. "A perplexity-based method for similar languages discrimination." Proceedings of the fourth workshop on NLP for similar languages, varieties and dialects (VarDial). 2017.

https://www.aclweb.org/anthology/W17-1213.pdf

Perplexity of fixed-length models — transformers 4.1.1 documentation

https://huggingface.co/transformers/perplexity.html