Comments on “Scheduling jobs on a k-stage flexible flow-shop”

The problem of makespan minimization on a flexible flow shop with k stages and m s machines at any stage proposed by Paternina-Arboleda et al. (2008) was recently published in Annals of Operations Research journal to solve the flexible flow-shop scheduling problems. In this work, some comments and suggestions are given to the paper. The comment is about the proposed mathematical formulation and the modification of it is suggested.