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<div class="moz-cite-prefix">I'm not sure what "an approximate
inverse to the original language model" means.<br>
<br>
But the purpose of ngram -expand-classes is to approximate the
class LM probabilities (the equation you give) using only word
ngram probabilities. It does so by inserting all expanded word
ngrams into the LM and giving them probabilities according to<br>
<br>
P(w_n | w_n-1 ... w_1) = P(w_n w_n-1 ... w_1) / P(w_n-1 ... w_1)<br>
<br>
where the joint probabilities on the right hand side are computed
by the class-based LM.<br>
<br>
Andreas<br>
<br>
On 5/16/2018 1:35 PM, Jonathan Mendoza wrote:<br>
</div>
<blockquote type="cite"
cite="mid:CAK=4f4mGGjU-VoDQWJMnWqOQqjSbJMv2Y3dWA0OEpSzFxCMJBQ@mail.gmail.com"><span
style="color:rgb(34,34,34);font-size:14px">SRILM community,</span>
<div style="color:rgb(34,34,34);font-size:14px"><br>
</div>
<div style="color:rgb(34,34,34);font-size:14px">If I build a class
based LM via </div>
<div style="color:rgb(34,34,34);font-size:14px"><br>
</div>
<div style="color:rgb(34,34,34);font-size:14px">replace-words-with-classes
-> ngram </div>
<div style="color:rgb(34,34,34);font-size:14px"><br>
</div>
<div style="color:rgb(34,34,34);font-size:14px">then re-build the
LM using -expand-classes,</div>
<div style="color:rgb(34,34,34);font-size:14px"><br>
</div>
<div style="color:rgb(34,34,34);font-size:14px">will the rebuilt
LM follow the class based probabilities,</div>
<div style="color:rgb(34,34,34);font-size:14px"><br>
</div>
<div style="color:rgb(34,34,34);font-size:14px">P(w_n | w_n-1 ...
w_1) ?= P(w_n | c_n) * P(c_n | c_n-1 ... c_1).</div>
<div style="color:rgb(34,34,34);font-size:14px"><br>
</div>
<div style="color:rgb(34,34,34);font-size:14px">Or is the mapping
an approximate inverse to the original language model?</div>
<br>
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<br>
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