[Opt-Mucca]

Description

This fixes #3561

The issue: We were comparing x <= x + feastol, where feastol was being swallowed by a large x. I've rearranged it to x - x <= feastol. The numerics should be a bit friendlier, and at least for this instance, it no longer returns an incorrect result. Edit: "this instance" is the one found in the issue

Checklist

• I have read the contributing guidelines
• This PR targets the latest branch
• Tests are passing
• Documentation was updated where relevant
• This PR is not primarily AI-generated (per the AI contributions policy in CONTRIBUTING.md)

Related issue

Closes #3561

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 75.71%. Comparing base (a9c6bed) to head (8ac0444).
⚠️ Report is 20 commits behind head on latest.

Additional details and impacted files

@@           Coverage Diff           @@
##           latest    #3575   +/-   ##
=======================================
  Coverage   75.70%   75.71%           
=======================================
  Files         461      461           
  Lines      114020   114012    -8     
  Branches    17933    17939    +6     
=======================================
- Hits        86322    86319    -3     
+ Misses      27410    27405    -5     
  Partials      288      288           

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[DoumarCharles]

Thanks for fixing this!

I initially wondered whether simply checking M <= b would be better. It leaves the full feasibility tolerance as a margin before the row could be considered violated. But I see the reasoning behind M - b <= feastol. It keeps the tolerance used throughout this code, and putting M and b on the same side avoids feastol being rounded away in b + feastol when b is large.

The change makes sense to me, and I'll follow the same logic in anything I suggest from now on.