Question in the video

Course Q&A Natural Language Processing NLP with Probabilistic Models
1

why is the right answer is the one with 1/4. the sentence length including special insertion is 5.
should not be log PP(W) = (-1/5)(-113) the right answer vs. log PP(W) = (-1/4)(-113)

Given the logarithm of these conditional probabilities:

log(P(Mary|))=-2

log(P(|cats))=-1

log(P(likes|Mary)) =-10

log(P(cats|likes))=-100

Assuming our test set is W=“ Mary likes cats ”, what is the model’s perplexity.

log PP(W) = (-1/5)*(-113)

log PP(W) = (-1/4)*(-113)

log PP(W) = -113

log PP(W) = (-1/5)*113

2

Hi @Fares_Bagh

What “video” are you talking about? (Which course, which week, Name of the video)

3

the video is : Language Model Evaluation

4

There is no video “Language Model Evaluation” in NLP Course2 Week2 (where your question is posted):
NLP with Probabilistic Models
W2: NLP with Probabilistic Models

5

my bad is week three

6

The answer to your original question is because we have 4 Bigrams in this particular case (5 words, but 4 Bigrams).

Cheers