  It is shown that the use of an external archive, purely for storage purposes,
can bring substantial benefits in multi-objective optimization. A new scheme
for archive management for the above purpose is described. The new scheme is
combined with the NSGA-II algorithm for solving two multi-objective
optimization problems, and it is demonstrated that this combination gives
significantly improved sets of Pareto-optimal solutions. The additional
computational effort because of the external archive is found to be
insignificant when the objective functions are expensive to evaluate.
