Fix L1 distance to use Manhattan sum

[SahilKumar75]

Summary

• compute L1 distance with a sum of absolute differences, matching the documented Manhattan-distance definition and l2's sum-based convention
• add a regression test covering dimensionality scaling and agreement on a simple case

Testing

• ruff check sbi/utils/metrics.py tests/metrics_test.py
• ruff format --check sbi/utils/metrics.py tests/metrics_test.py
• direct l1/l2 Manhattan-distance regression passed
• full metrics test module could not be collected in this environment because pytest_harvest and nflows are unavailable

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro Plus

Run ID: 9976e788-7f82-4c0f-8d80-b8b0200d6588

📥 Commits

Reviewing files that changed from the base of the PR and between 900821d and 69df3b4.

📒 Files selected for processing (2)

• sbi/utils/metrics.py
• tests/metrics_test.py

Included review availability: Your plan provides up to 4 included reviews per hour; 3 remain after this review.

---

📝 Walkthrough

Walkthrough

The l1 metric now computes non-averaged Manhattan distance by summing absolute differences along the selected axis. Regression tests verify behavior when identical dimensions are added.

Changes

Metric distance behavior

Layer / File(s)	Summary
Update L1 distance and regression coverage sbi/utils/metrics.py, tests/metrics_test.py	l1 now sums absolute differences instead of averaging them. Tests verify the expected distance for one differing dimension and additional identical dimensions.

Estimated code review effort: 2 (Simple) | ~10 minutes

Merge Risk: ⚪ Minimal · up to 69df3

This change corrects L1 distance to use the documented Manhattan sum and adds regression coverage. No actionable merge-blocking risk remains beyond normal checks and review.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely describes the primary change to use the Manhattan sum for L1 distance.
Description check	✅ Passed	The description explains the behavior change, regression test, and validation results, but it omits several template sections and checklist items.
Docstring Coverage	✅ Passed	Docstring check was indeterminate for this PR — some files could not be analyzed in time. Not blocking.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

---

Thanks for using CodeRabbit! It's free for OSS, and your support helps us grow. If you like it, consider giving us a shout-out.

❤️ Share

• X
• Mastodon
• Reddit
• LinkedIn

_{Comment @coderabbitai help to get the list of available commands.}

[SahilKumar75]

The focused regression change is ready for maintainer review. The test suite coverage and formatting checks are complete.