YinzOR 2025 Pittsburgh

Events

Marion Technical Writer July 17, 2025

Hexaly is delighted once again to be the premier sponsor of the YinzOR 2025 conference. The event will occur from August 29 to 30, 2025, at Carnegie Mellon University, Pittsburgh. The YinzOR 2025 conference program can be accessed here.

Meet Fred Gardi, Founder & CEO of Hexaly, at YinzOR 2025, and discover the new release Hexaly 14.0, which delivers dramatic performance improvements for solving Routing, Scheduling, Packing, Clustering, Assignment, Location, and many other problems in Supply Chain and Workforce Optimization. This is also the opportunity to explore and discuss our many job offers. Below are the abstracts of Fred’s talks at the 2025 YinzOR Conference.

Computing dual bounds for set-based models using column generation and column elimination in Hexaly

Friday, August 29th, 2025, 3:45pm-4:25pm – 3801 Swartz Center

Hexaly is a model-and-run solver that integrates heuristics and exact methods. A set and permutation-based modeling formalism was introduced to simplify the modeling of combinatorial problems, like routing or packing problems. For instance, in a routing problem, list variables can be used to model the sequence of visits made by each truck. These decision variables are suited for a heuristic search but are much more challenging to integrate into a mathematical programming approach to compute lower bounds. A direct reformulation in a MILP model introduces a quadratic number of binary decisions with several big M constraints, leading to poor scalability and bounds. Hexaly automatically detects such structures in a user model and reformulates them in an extended MILP model to compute lower bounds parallel to a heuristic search. This model is solved efficiently using state-of-the-art branch-and-cut-and-price techniques and column elimination algorithms. This talk will present the general approach, the algorithms used for the resolution, and some benchmarks on the classical vehicle routing and packing problems.

We look forward to connecting with the operations research community at YinzOR in Pittsburgh.