Cover more cases of log1mexp stabilization

[lciti]

This PR fixes #1476 by reimplementing the rewrite log1pmexp_to_log1mexp using is_neg so it works with neg() as well as mul(-1.0, ...), which is the canonicalised form. It adds a test for #1476 (which now passes) as well as other tests for expressions that should simplify to log1mexp (I realised that expressions like log(-exp(x) + 1) would not work). It then implements the missing rewrite log(-expm1(x)) -> log1mexp(x) to make these additional tests pass.

Description

Related Issue

• Closes The rewrite log1pmexp_to_log1mexp is not applied #1476

Checklist

• Checked that the pre-commit linting/style checks pass
• Included tests that prove the fix is effective or that the new feature works
• Added necessary documentation (docstrings and/or example notebooks)
• If you are a pro: each commit corresponds to a relevant logical change

Type of change

• New feature / enhancement
• Bug fix
• Documentation
• Maintenance
• Other (please specify):

---

📚 Documentation preview 📚: https://pytensor--1483.org.readthedocs.build/en/1483/

[ricardoV94]

Looks good, just a question about readability at the cost of performance. We can merge as is if you disagree

[lciti]

I am not sure if you noticed, there is an opportunity to implement log1pexp_to_softplus directly within log1pmexp_to_log1mexp (which could be called log1p_pm_exp_to_log1pexp_log1mexp or sth like that) and get rid of a separate log1pexp_to_softplus function. The only disadvantage would be the inability to include/exclude just one of the two rewrites. Please let me know what you prefer.

[ricardoV94]

Yeah I think we can merge them, they're similar in nature

[lciti]

I think it's ready to go.

[ricardoV94]

Great, running tests

[lciti]

Ops, I think found a mistake. I'll commit asap.

[codecov]

Codecov Report

❌ Patch coverage is 95.45455% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 82.01%. Comparing base (6aeed97) to head (9f9bc8b).
⚠️ Report is 122 commits behind head on main.

Files with missing lines	Patch %	Lines
pytensor/tensor/rewriting/math.py	95.45%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@ Coverage Diff @@ ## main #1483 +/- ## ========================================== + Coverage 82.00% 82.01% +0.01%  ========================================== Files 214 214 Lines 50413 50431 +18 Branches 8902 8907 +5 ========================================== + Hits 41342 41362 +20  + Misses 6863 6861 -2  Partials 2208 2208 

Files with missing lines	Coverage Δ
pytensor/tensor/rewriting/math.py	89.49% <95.45%> (+0.24%)	⬆️

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[ricardoV94]

Thanks @lciti ! Let us know if you find more things to tweak

[lciti]

Many thanks to you for your support and, more in general, for developing/maintaining such an invaluable research tool!