192
IEEE TRANSACTIONS ON EVOLUTIONARY COMPUTATION, VOL. 6, NO. 2, APRIL 2002
Fig. 13.
Obtained nondominated solutions with NSGA-II, PAES, and SPEA
on the rotated problem.
within the prescribed variable bounds, we discourage solutions
with
by adding a fixed large penalty to both objec-
tives. Fig. 13 shows the obtained solutions at the end of 500
generations using NSGA-II, PAES, and SPEA. It is observed
that NSGA-II solutions are closer to the true front compared
to solutions obtained by PAES and SPEA. The correlated pa-
rameter updates needed to progress toward the Pareto-optimal
front makes this kind of problems difficult to solve. NSGA-II’s
elite-preserving operator along with the real-coded crossover
and mutation operators is able to find some solutions close to the
Pareto-optimal front [with
resulting
].
This example problem demonstrates that one of the known dif-
ficulties (the
linkage problem [11], [12]) of single-objective op-
timization algorithm can also cause difficulties in a multiobjec-
tive problem. However, more systematic studies are needed to
amply address the linkage issue in multiobjective optimization.
VI. C
ONSTRAINT
H
ANDLING
In the past, the first author and his students implemented a
penalty-parameterless constraint-handling approach for single-
objective optimization. Those studies [2], [6] have shown how
a tournament selection based algorithm can be used to handle
constraints in a population approach much better than a number
of other existing constraint-handling approaches. A similar ap-
proach can be introduced with the above NSGA-II for solving
constrained multiobjective optimization problems.
Chia sẻ với bạn bè của bạn: