Preface: Introducing operations research trends at CLAIO XVIII.

In the paper, "An exact algorithm for the edge coloring by total labeling problem", Borghini, Méndez-Díaz, and Zabala address the edge coloring problem, a classical problem in graph theory. The problem is modeled as a mixed integer nonlinear programming problem considering maximum number of orders, capacity, and budget constraints. In the paper, "A two-level evolutionary algorithm for solving the petrol station replenishment problem with periodicity constraints and service choice", Al-Hinai and Triki address the petrol station replenishment problem with periodicity constraints and introduce the frequency service choice as a decision variable. Arpón, Homem-de-Mello, and Pagnoncelli in their paper, "An ADMM algorithm for two-stage stochastic programming problems", show that the Alternate Direction Method of Multipliers (ADMM) can be applied to solve two-stage stochastic programming problems, and propose an implementation in three blocks, with or without proximal terms, that can be used as an algorithm to solve convex problems with a block structure. [Extracted from the article]