What are Big M constraints? [dual]

This post presents a class of constraints that are used very often in mixed-integer programming (MIP) models. I explain what they are, why they are important and why using too large values for the big M is problematic. The associated primal post presents some experiments that outline how modern solvers handle unnecessarily large values of […]

Facility location : not so difficult (with the proper tools)

In a previous post, I generated a few capacitated facility location instances (CFLP) and I ran these through MIP solvers. The instances were solved pretty quickly overall. In a comment, professor Matteo Fischetti suggested I compare my results with some instances from the literature, which I did. Overall, the results are quite fast; CPLEX takes only 21 […]

Facility location : mistake, issue and results

About two weeks ago, I generated a few capacitated facility location instances (CFLP) for some students to play with. When I ran these through the CPLEX and Gurobi solvers, all of them were solving very quickly. Gurobi in fact seemed to find the optimal solution during the presolve stage. I made a quick blog post […]

Facility location : presolved to optimality!

  ** IMPORTANT NOTICE ** This post has temporarily been suspended as some readers noticed potential problem with the model files. I will issue a corrected post shortly. I am sorry for any inconvenience. Marc-André

Supply chain network design in 500 words

I’ve spent more time working on supply chain network (SCN) design problems than any other. This post summarizes the topic. What is supply chain network design? SCN design is a strategic problem arising in logistics and supply chain management. Typical SCN design problems involves strategic decisions on the number, location, capacity and missions of the […]

Can the CPLEX tuning tool help solving hard models?

The CPLEX MIP Solver has had a tuning tool for some time. For those new to the concept, the tuning tool tries different parameter settings and seeks to find good parameters for the solver for a given optimization model. I have tested the tuning tool on 10 relatively difficult-to-solve models. By difficult, I mean models […]