In the procedure above, F_1, F_2,y are called nondominated fronts, and F_1 is the Pareto front of population P. NSGA [10] also classifies the population into nondominated fronts using an algorithm similar to that given above. Then a dummy fitness value is assigned to each front using a fitness sharing function such that the worst fitness value assigned to F_ is better than the best fitness value assigned to F_+1. NSGA-II [16], a more efficient algorithm, named the fast non-dominated-sort algorithm, was developed to form non-dominated fronts. Fonseca and Fleming [6] used a slightly different rank assignment approach than the ranking based on non-dominated-fronts as follows: