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Perplexity of n-gram and dependency language models

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Language Models – basics<br />

P(s) = P(w 1, w 2, ... w m) = P(w 1) P(w 2|w 1) … P(w m|w 1,...,w m-1)<br />

P( The dog barked again ) =<br />

P(wi = The | i=1, wi-1 = NONE ) ·<br />

P(wi = | i=2, wi-2 = NONE<br />

, wi-1 = The ) ·<br />

dog<br />

Artificial start-<strong>of</strong>-sentence token<br />

P(wi = barked | i=3, wi-3 = NONE , wi-2 = The , wi-1 = dog ) ·<br />

P(wi = again | i=4, wi-4 = NONE , wi-3 = The , wi-2 = dog , wi-1 = barked )<br />

8

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