Main merge release/26.02 5

[rgsl888prabhu]

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

Summary by CodeRabbit

• New Features

  • Added reliability_branching parameter to control reliability-based variable selection strategy in MIP solver.

• Improvements

  • Enhanced branch variable selection through improved pseudocost scoring and reliable selection mechanisms.
  • Refined multi-threaded branch-and-bound execution with worker pool-based architecture.
  • Simplified configuration for sub-problem solving in diversity heuristics.

• Refactor

  • Reorganized internal branch-and-bound worker management for improved parallel execution coordination.

[coderabbitai]

Caution

Review failed

The pull request is closed.

📝 Walkthrough

Walkthrough

This PR introduces a scheduler-worker paradigm for branch-and-bound optimization, adds reliability branching parameter configuration, refactors diving/best-first threading logic, enhances pseudo-cost calculations, and updates utility classes for thread safety. Key changes span solver settings, worker pool management, pseudo-cost strategies, and configuration simplification in related solvers.

Changes

Cohort / File(s)	Summary
Reliability Branching Configuration benchmarks/linear_programming/cuopt/run_mip.cpp, cpp/include/cuopt/linear_programming/constants.h, cpp/include/cuopt/linear_programming/mip/solver_settings.hpp, cpp/src/dual_simplex/simplex_solver_settings.hpp, cpp/src/math_optimization/solver_settings.cu	Added reliability_branching parameter as a new configurable integer (-1 default) throughout the MIP solver, enabling control over reliability-based variable selection strategy.
Branch-and-Bound Worker Architecture cpp/src/dual_simplex/branch_and_bound_worker.hpp, cpp/src/dual_simplex/branch_and_bound.hpp, cpp/src/dual_simplex/branch_and_bound.cpp	Introduced new worker-pool and scheduler-based design replacing per-thread enum model; added branch_and_bound_worker_t, branch_and_bound_worker_pool_t, and search_strategy_t; refactored core solving API to use worker pointers and new orchestration methods (run_scheduler, single_threaded_solve, plunge_with, dive_with); removed bnb_worker_type_t and bnb_stats_t.
Pseudo-Cost and Variable Selection cpp/src/dual_simplex/pseudo_costs.hpp, cpp/src/dual_simplex/pseudo_costs.cpp	Added reliable_variable_selection method with dynamic reliability threshold, trial_branching helper, atomic-backed pseudo-cost containers with per-variable mutexes, and calculate_pseudocost_score function; refactored objective estimation and strong branching handling.
Diving Heuristics Updates cpp/src/dual_simplex/diving_heuristics.cpp	Removed mutex acquisition in pseudocost and guided diving; added fallback mechanism to select first fractional variable when all scores yield NONE; changed max_score initialization from lowest() to -1.
Core Utilities cpp/src/utilities/omp_helpers.hpp, cpp/src/utilities/pcgenerator.hpp	Refactored omp_mutex_t to use unique_ptr with move semantics and explicit rule-of-five; made omp_atomic_t conversion operator const-qualified; introduced new CPU-side PCG random number generator (pcgenerator_t).
Solver Settings and Configuration cpp/src/mip/diversity/lns/rins.cu, cpp/src/mip/diversity/recombiners/sub_mip.cuh, cpp/src/mip/solver.cu, cpp/src/dual_simplex/simplex_solver_settings.hpp	Simplified RINS and SubMIP branch-and-bound configurations to single-threaded setup with reliability_branching; removed num_bfs_workers and num_diving_workers; updated solver to wire reliability_branching and mip_batch_pdlp_strong_branching; refined thread count computation.
Data Structure Updates cpp/src/dual_simplex/solution.hpp, cpp/src/dual_simplex/node_queue.hpp, cpp/src/dual_simplex/mip_node.hpp, cpp/src/dual_simplex/basis_updates.hpp, cpp/src/dual_simplex/presolve.cpp	Widened nodes_explored and simplex_iterations to int64_t; made node_queue pop methods thread-safe with mutex; rewrote mip_node detach_copy for explicit field copying; added copy/move constructors and set_refactor_frequency to basis_update_mpf_t; changed bounds strengthening to compile-time conditional.

Estimated code review effort

🎯 4 (Complex) | ⏱️ ~65 minutes

Possibly related PRs

• Scheduler-Worker Model + Reliability Branching #766: Directly related implementation of scheduler–worker refactoring and reliability_branching parameter wiring across branch-and-bound, pseudo-costs, and solver settings with matching file/function signature changes.

Suggested labels

improvement, mip

Suggested reviewers

• akifcorduk
• chris-maes

✨ Finishing touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment

---

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 and usage tips.}