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https://issues.apache.org/jira/browse/LUCENE-1534?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12669754#action_12669754
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Doug Cutting commented on LUCENE-1534:
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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: https://issues.apache.org/jira/browse/LUCENE-1534
> 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:
>
> http://lucene.apache.org/java/2_4_0/api/org/apache/lucene/search/Similarity.html
> 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:
> http://markmail.org/message/k5pl7scmiac5wosb
> Or am I missing something? We just need to fix the javadocs to take
> away the "squared"...
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