[LUCENE-7776] Switch KNN classifier to use BM25 similarity

• Type: Improvement
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 7.0
• Component/s: modules/classification
• Lucene Fields: New
• Assignee: Tommaso Teofili
• Reporter: Tommaso Teofili
• Created: 11/Apr/17 08:22
• Updated: 28/Aug/22 15:13
• Resolved: 11/Apr/17 08:45

Description

It'd be good to use BM25 as default Similarity for KNN classifier.
Having done some tests on the 20newsgroups dataset that resulted in improved f1 (between 0.10 and 0.15).