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From "Doug Cutting (JIRA)" <>
Subject [jira] Commented: (LUCENE-1534) idf(t) is not actually squared during scoring?
Date Mon, 02 Feb 2009 21:43:59 GMT


Doug Cutting commented on LUCENE-1534:

sumOfSquaredWeights properly normalizes query vectors to the unit sphere.  We can't easily
do that with document vectors, since idfs change as the collection changes.  So we instead
use a heuristic to normalize documents, sqrt(numTokens), which is usually a good approximation.
 Regardless of how it's normalized, the global term weight factors twice in each addend, once
from each vector.

> idf(t) is not actually squared during scoring?
> ----------------------------------------------
>                 Key: LUCENE-1534
>                 URL:
>             Project: Lucene - Java
>          Issue Type: Bug
>          Components: Query/Scoring
>    Affects Versions: 2.1, 2.2, 2.3, 2.3.1, 2.3.2, 2.4
>            Reporter: Michael McCandless
>            Assignee: Michael McCandless
>            Priority: Minor
>             Fix For: 2.9
> The javadocs for Similarity:
> show idf(t) as being squared when computing net query score.  But I
> don't think it is actually squared, in looking at the sources?  Maybe
> it used to be, eg this interesting discussion:
> Or am I missing something?  We just need to fix the javadocs to take
> away the "squared"...

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