“…To test how difficult it is to solve an instance we have on the one hand, two effective algorithms for the permutation flowshop scheduling problem with the objective to minimise the makespan (Ruiz et al, 2006 andStützle, 2007). On the other hand, four lower bounds, one from Taillard (1993) and the three best polynomial bounds of Ladhari and Haouari (2005), proposed for the same problem, are computed for each instance. All the generated instances (48,000 small and 24,000 large) are solved by the two effective algorithms, denoted as HGA (Ruiz et al, 2006) and IG (Ruiz and Stützle, 2007), since they are considered the most effective for this problem.…”