Understanding Elasticsearch TF/IDF score in 6.8

Elastic Stack Elasticsearch
1

Hi,
I was looking at the lucene TF/IDF practical scoring function vs what is reported in the ES explain API. For ES 6.8, it used lucence 7.x for calculating the TF/IDF score which has a squared IDF term

Screen Shot 2020-03-10 at 4.21.04 PM
Screen Shot 2020-03-10 at 4.21.04 PM990×296 18.3 KB

However, when I look at the explain results for 6.8, I just see one idf term instead of a squared idf.

Screen Shot 2020-03-17 at 5.22.30 PM
Screen Shot 2020-03-17 at 5.22.30 PM1926×1426 235 KB

Am I missing something or is there a missing idf term in explain?

2

By default I believe Elasticsearch 6.8 uses BM25 instead of TF/IDF. What does your query look like?

3

I have set the similarity module to classic i.e. TF/IDF

4

The query has just a single term.

5

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