[CS241] Asgn2 questions

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No. You shouldn't look at the tense of sentence j-1.

On 9/23/07, Avram Levi <avramlevi at lems.brown.edu> wrote:
>
> Justin (and everyone else)
>
> I still have a hard time understanding some minor aspects of part d. Say
> we have the tenses A, B, C, D and we have a sequence:
>
> A A B A C B A C B A B B A...
>
> say we are looking for p(B|A) then to my understanding, although A
> occured in sentence 1, the first B(in sentence 3) doesn't count because
> A also occured in sentence 2 which is right before the B. On the other
> hand, the second B(in sentence 6) counts because the previous tense was
> a C - is that right?
>
> in other words when you say "any but the previous sentence" should we
> make sure that the given tense doesn't occur in sentence j-1?
>
> Thanks,
> Avram
>
> Justin Palmer wrote:
>
> >Hi Lenora,
> >
> >Here's my take on your questions.  I might be wrong...
> >
> >For KL divergence, yes, order matters.  D(p || q) != D(q || p).
> >That's why KL divergence is not a distance/metric.  So, I'm using the
> >order Eugene asked for in the assignment, e.g, D( p(tense) || p(tense
> >| tense in prev sent) ).  Regarding the log(0) issue, I ran into it
> >too; my understanding is that for entropy calculations, we define 0 *
> >log 0 = 0.
> >
> >To compute D( p(tense) || p(tense|tense in prev sent) ), I did:
> >
> >   KL += p(tense) * log (p(tense) / p(tense | tense in prev sent))
> >
> >for all tenses.  So we get 2 numbers saying how useful the two
> >conditional probability distributions are as predictors of tense.
> >Does that make sense?
> >
> >I understand part d to mean calculate p(tense | tense any but prev
> >sent).  I'm computing:
> >
> >  P(past | past), P(future | past), etc.
> >
> >So if you're at sentence i, and it's past, and a past tense also
> >occurred in any of the previous sentences other than the last one,
> >that counts.  Also, if a future occurred in any sentence other than
> >the previous sentence, add another count.  And so on.
> >
> >If you'd like to to compare numbers, please let me know.
> >
> >Also, is anyone else having problems with the Tree::newstory flag?
> >Appears that it never gets set, but I'm probably missing something
> >obvious.
> >
> >Thanks,
> >
> >  -- j
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> >
> >
> >
> >
>
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