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I'm asked to implement "Interpolated Absolute Discounting" for a bigram language model for a text. First, I don't know what is it exactly. I guess it is an interpolation between different ngrams (unigram, bigram, ), whose parameters needs to be learned

Second, what is the implemented probability distribution for this technique in nltk package?

Moreover, I must learn the parameters from a corpus. How can I do that?

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It might be back to the Kneser–Ney smoothing (which is used absolute discounting). And you can find it in Kneser-Ney probability distribution using the following code as an example (from this post):

from nltk.util import ngrams
from nltk.corpus import gutenberg

gut_ngrams = ( ngram for sent in gutenberg.sents() for ngram in ngrams(sent, 3, pad_left = True, pad_right = True, right_pad_symbol='EOS', left_pad_symbol="BOS"))
freq_dist = nltk.FreqDist(gut_ngrams)
kneser_ney = nltk.KneserNeyProbDist(freq_dist)
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