As Deb and Et al. illustrated in the attached article, unlike the NSGA2 in which we use Crowding distance method to choose the next generation in GA, the NSGA3 uses associated reference point to choose the remaining population from the current one to form the next generation.

each reference point(j) has a specific NO of associated member called (ρj).

if ρj=0 it means that non of the members are associated with jth reference point, but in the part G of section IV of the article, this condition is defined with 2 scenarios wich are not so obvious.

can any one tell me how can ρj be zero and still there is an associated member in the last front ????