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https://issues.apache.org/jira/browse/LUCENE-8011?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Adrien Grand resolved LUCENE-8011.
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Resolution: Fixed
Fix Version/s: master (8.0)
> Improve similarity explanations
> -------------------------------
>
> Key: LUCENE-8011
> URL: https://issues.apache.org/jira/browse/LUCENE-8011
> Project: Lucene - Core
> Issue Type: Improvement
> Reporter: Robert Muir
> Labels: newdev
> Fix For: master (8.0)
>
>
> LUCENE-7997 improves BM25 and Classic explains to better explain:
> {noformat}
> product of:
> 2.2 = scaling factor, k1 + 1
> 9.388654 = idf, computed as log(1 + (N - n + 0.5) / (n + 0.5)) from:
> 1.0 = n, number of documents containing term
> 17927.0 = N, total number of documents with field
> 0.9987758 = tf, computed as freq / (freq + k1 * (1 - b + b * dl / avgdl))
> from:
> 979.0 = freq, occurrences of term within document
> 1.2 = k1, term saturation parameter
> 0.75 = b, length normalization parameter
> 1.0 = dl, length of field
> 1.0 = avgdl, average length of field
> {noformat}
> Previously it was pretty cryptic and used confusing terminology like
> docCount/docFreq without explanation:
> {noformat}
> product of:
> 0.016547536 = idf, computed as log(1 + (docCount - docFreq + 0.5) /
> (docFreq + 0.5)) from:
> 449.0 = docFreq
> 456.0 = docCount
> 2.1920826 = tfNorm, computed as (freq * (k1 + 1)) / (freq + k1 * (1 - b + b
> * fieldLength / avgFieldLength)) from:
> 113659.0 = freq=113658
> 1.2 = parameter k1
> 0.75 = parameter b
> 2300.5593 = avgFieldLength
> 1048600.0 = fieldLength
> {noformat}
> We should fix other similarities too in the same way, they should be more
> practical.
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