Fix incorrect errors with x + x*x, +x, -x in Python API

[chris-maes]

Description

Issue

Checklist

• I am familiar with the Contributing Guidelines.
• Testing
  • New or existing tests cover these changes
  • Added tests
  • Created an issue to follow-up
  • NA
• Documentation
  • The documentation is up to date with these changes
  • Added new documentation
  • NA

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[chris-maes]

/ok to test 72cdcd7

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📥 Commits

Reviewing files that changed from the base of the PR and between 4253db3 and d21f55f.

📒 Files selected for processing (1)

• python/cuopt/cuopt/linear_programming/problem.py

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📝 Walkthrough

Walkthrough

Adds unary negation (__neg__) and unary plus (__pos__) to Variable, and extends Variable.__add__ and Variable.__sub__ to delegate to QuadraticExpression when that type appears on the other operand, enabling commutative addition and compatible subtraction with quadratic expressions.

Changes

Cohort / File(s)	Summary
Variable operator updates python/cuopt/cuopt/linear_programming/problem.py	Added Variable.__neg__ to return a LinearExpression representing -self; added Variable.__pos__ to return self; extended Variable.__add__ to handle QuadraticExpression by returning other + self; extended Variable.__sub__ to handle QuadraticExpression by returning other * -1.0 + self.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

🚥 Pre-merge checks | ✅ 1 | ❌ 2

❌ Failed checks (1 warning, 1 inconclusive)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 20.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.
Description check	❓ Inconclusive	The description field is empty except for the contribution template; it provides no meaningful information about the changeset.	Add a brief description of the bug being fixed and the solution implemented to clarify the PR's purpose.

✅ Passed checks (1 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly summarizes the main changes: adding support for unary operators (+x, -x) and mixed expression operations (x + x*x) in the Python API.

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[chris-maes]

/ok to test 4253db3

[Iroy30]

/ok to test 359c81e

[chris-maes]

/merge

[chris-maes]

/ok to test 359c81e

[chris-maes]

/merge

[chris-maes]

/ok to test f7f2301