Furthermore, taking a look to the code for BM25 similarity, it seems to me it
is currently working right :
- docCount is used per field if != -1
/**
* Computes a score factor for a simple term and returns an explanation
* for that score factor.
*
* <p>
* The default implementation uses:
*
* <pre class="prettyprint">
* idf(docFreq, docCount);
* </pre>
*
* Note that {@link CollectionStatistics#docCount()} is used instead of
* {@link org.apache.lucene.index.IndexReader#numDocs()
IndexReader#numDocs()} because also
* {@link TermStatistics#docFreq()} is used, and when the latter
* is inaccurate, so is {@link CollectionStatistics#docCount()}, and in
the same direction.
* In addition, {@link CollectionStatistics#docCount()} does not skew when
fields are sparse.
*
* @param collectionStats collection-level statistics
* @param termStats term-level statistics for the term
* @return an Explain object that includes both an idf score factor
and an explanation for the term.
*/
public Explanation idfExplain(CollectionStatistics collectionStats,
TermStatistics termStats) {
final long df = termStats.docFreq();
final long docCount = collectionStats.docCount() == -1 ?
collectionStats.maxDoc() : collectionStats.docCount();
final float idf = idf(df, docCount);
return Explanation.match(idf, "idf, computed as log(1 + (docCount -
docFreq + 0.5) / (docFreq + 0.5)) from:",
Explanation.match(df, "docFreq"),
Explanation.match(docCount, "docCount"));
}
-----
---------------
Alessandro Benedetti
Search Consultant, R&D Software Engineer, Director
Sease Ltd. - www.sease.io
--
Sent from: http://lucene.472066.n3.nabble.com/Solr-User-f472068.html
