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https://issues.apache.org/jira/browse/LUCENE-8020?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16223682#comment-16223682
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Robert Muir commented on LUCENE-8020:
-------------------------------------
I noticed this when trying to debug AfterEffectB in LUCENE-8015.
The formula should be: {{(F + 1) / (n * (tfn + 1))}} but we currently use {{(F
+ 1 + 1) / ((n + 1) * (tfn + 1))}} and I couldn't remember why we had this mess
everywhere.
> Don't force sim to score bogus terms (e.g. docfreq=0)
> -----------------------------------------------------
>
> Key: LUCENE-8020
> URL: https://issues.apache.org/jira/browse/LUCENE-8020
> Project: Lucene - Core
> Issue Type: Bug
> Reporter: Robert Muir
>
> Today all sim formulas have to be "hacked" to deal with the fact that they
> may be passed stats such as docFreq=0, totalTermFreq=0. This happens easily
> with spans and there is even a dedicated test for it. All formulas have hacks
> such as what you see in https://issues.apache.org/jira/browse/LUCENE-6818:
> Instead of:
> {code}
> expected = stats.getTotalTermFreq() * docLen / stats.getNumberOfFieldTokens();
> {code}
> they must do tricks such as:
> {code}
> expected = (1 + stats.getTotalTermFreq()) * docLen / (1 +
> stats.getNumberOfFieldTokens());
> {code}
> There is no good reason for this, it is just sloppiness in the
> Query/Weight/Scorer api. I think formulas should work unmodified, we
> shouldn't pass terms that dont exist or bogus statistics.
> It adds a lot of complexity to the scoring api and makes it difficult to have
> meaningful/useful explanations, to debug problems, etc. It also makes it
> really hard to add a new sim.
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