shubhamvishu opened a new pull request, #12726: URL: https://github.com/apache/lucene/pull/12726
### Description While going through [VectorUtil](https://github.com/apache/lucene/blob/main/lucene/core/src/java/org/apache/lucene/util/VectorUtil.java) class, I observed we don't have a check for unit vector in `VectorUtil#l2normalize` so passing a unit vector goes thorough the whole L2 normalization(which is totally not required and it should early exit?). I confirmed this by trying out a silly example of `VectorUtil.l2normalize(VectorUtil.l2normalize(nonUnitVector))` and it performed every calculation twice. We could also argue that user should not call for this for a unit vector but I believe there would be cases where user simply want to perform the L2 normalization without checking the vector or if there are some overflowing values. TL;DR : We should early exit in `VectorUtil#l2normalize`, returning the same input vector if its a unit vector This is easily avoidable if we introduce a light check to see if the L1 norm or squared sum of input vector is equal to 1.0 (or) maybe just check `Math.abs(l1norm - 1.0d) <= 1e-5` (as in this PR) because that unit vector dot product(`v x v`) are not exactly 1.0 but like example : `0.9999999403953552` etc. With `1e-5` delta here we would be assuming a vector v having `v x v` >= `0.99999` is a unit vector or say already L2 normalized which seems fine as the delta is really small? and also the check is not heavy one?. I'm not sure this there existed some sort of similar check before or something(I tried to check but didn't find any history) so looking forward to thoughts if this makes sense to be added or not. Thanks! <!-- If this is your first contribution to Lucene, please make sure you have reviewed the contribution guide. https://github.com/apache/lucene/blob/main/CONTRIBUTING.md --> -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: issues-unsubscr...@lucene.apache.org For queries about this service, please contact Infrastructure at: us...@infra.apache.org --------------------------------------------------------------------- To unsubscribe, e-mail: issues-unsubscr...@lucene.apache.org For additional commands, e-mail: issues-h...@lucene.apache.org
