Formal models and scripts: lmdirichlet-mu-zero-limit-and-multisimilarity-norm-combsum

Tools: Python

These are the working models and scripts this part of the hunt used. Some encode the code as it is (a counterexample is the expected result), others a fixed or correct variant; read the header comment of each file. Paths inside them were replaced by placeholders such as $LUCENE (a Lucene checkout) and $WORK.

Findings

• LMDirichletSimilarity accepts mu = 0, but then every document scores 0: log(1 + tf/(mu*P)) + log(mu/(dl+mu)) becomes +Infinity + -Infinity = NaN, and the 'score > 0' clamp turns NaN into 0 (finding LFV-902; repro · finding page)

Files

• model/lmdirichlet_mu0.py (used for LFV-902)

How to run

• Python: python3 <file>.py; scripts that import z3 need the z3-solver package.

Snapshot of 2026-11-04. AI-assisted; not yet triaged by a human Lucene committer. Feedback: open an issue in lucene-ai-bug-hunt.