Add a hyperparameter that controls bounding of free variables

[yuwenchen95]

Description

Adds a new solver setting, barrier_presolve_bound_free_variables
(CUOPT_BARRIER_PRESOLVE_BOUND_FREE_VARIABLES), that controls whether barrier
presolve bounds free variables (-1 automatic/current default behavior,
0 disabled, 1 enabled).

Issue

Closes #1711

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📥 Commits

Reviewing files that changed from the base of the PR and between 6a5dcbf and c20a4bc.

📒 Files selected for processing (7)

• cpp/include/cuopt/mathematical_optimization/constants.h
• cpp/include/cuopt/mathematical_optimization/pdlp/solver_settings.hpp
• cpp/src/dual_simplex/presolve.cpp
• cpp/src/dual_simplex/simplex_solver_settings.hpp
• cpp/src/math_optimization/solver_settings.cu
• cpp/src/pdlp/solve.cu
• cpp/tests/linear_programming/unit_tests/solver_settings_test.cu

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📝 Walkthrough

Walkthrough

Adds a configurable barrier_presolve_bound_free_variables setting with automatic, disabled, and enabled modes. Propagates the setting to barrier presolve, gates free-variable bound inference, and tests its values.

Changes

Barrier presolve control

Layer / File(s)	Summary
Setting contract and registration cpp/include/cuopt/mathematical_optimization/constants.h, cpp/include/cuopt/mathematical_optimization/pdlp/solver_settings.hpp, cpp/src/dual_simplex/simplex_solver_settings.hpp, cpp/src/math_optimization/solver_settings.cu	Defines and registers barrier_presolve_bound_free_variables. The setting defaults to -1, with 0 disabling and 1 enabling the behavior.
Barrier propagation and presolve behavior cpp/src/pdlp/solve.cu, cpp/src/dual_simplex/presolve.cpp	Forwards the setting to barrier solver options. Free-variable bound inference now requires a nonzero setting and free variables.
Setting value validation cpp/tests/linear_programming/unit_tests/solver_settings_test.cu	Tests the default, disabled, and enabled assignments.

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

Mergeability Score: 🔵 Low · up to c20a4

The new solver setting is localized, but adding it to the public settings structure may affect C++ compatibility and requires the documented modes and default behavior to be confirmed. The PR is mergeable with explicit owner awareness or follow-up on that bounded API concern.

Suggested reviewers: ramakrishnap-nv, chris-maes, rg20

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly describes the main change: adding a setting to control free-variable bounding.
Description check	✅ Passed	The description accurately explains the new setting, its modes, and the linked issue.
Linked Issues check	✅ Passed	The changes implement the requested -1, 0, and 1 modes for controlling barrier presolve free-variable bounding [#1711].
Out of Scope Changes check	✅ Passed	The changes remain within scope and include only the new setting, its propagation, behavior, formatting, and tests.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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CI Test Summary

✅ All 31 test job(s) passed.