978-1-4673-7679-2/15/$31.00 ©2015 IEEE 330
2015 11th International Conference on Natural Computation (ICNC)
An Opposition-based Repair Operator for
Multi-objective Evolutionary Algorithm in
Constrained Optimization Problems
Zhun Fan
Department of Electronic Engineering
Shantou University
Guangdong, Shantou 515063
Han Huang
School of Software Engineering
South China University of
Technology, Guangdong, Guangzhou 510006
Wenji Li
Department of Electronic Engineering
Shantou University
Guangdong, Shantou 515063
Shuxiang Xie
Department of Electronic Engineering
Shantou University
Guangdong, Shantou 515063
Xinye Cai
College of Computer Science and
Technology, Nanjing University of
Aeronautics and Astronautics
Jiangsu, Nanjing 210016
Erik Goodman
BEACON Centre for the Study of
Evolution in Action, Michigan State
University, East Lansing, MI, 48824
Abstract—In this paper, we design a set of multi-objective
constrained optimization problems (MCOPs) and propose a new
repair operator to address them. The proposed repair operator
is used to fix the solutions that violate the box constraints. More
specifically, it employs a reversed correction strategy that can
effectively avoid the population falling into local optimum. In
addition, we integrate the proposed repair operator into two
classical multi-objective evolutionary algorithms MOEA/D and
NSGA-II. The proposed repair operator is compared with other
two kinds of commonly used repair operators on benchmark
problems CTPs and MCOPs. The experiment results demon-
strate that our proposed approach is very effective in terms of
convergence and diversity.
Index Terms—Multi-objective Evolutionary Algorithm, Repair
Operator, Constrained Optimization.
I. INTRODUCTION
Multi-objective optimization problems (MOPs) consist of
more than one objectives, which are usually conflicting with
each other. In other words, improvements in one objective may
lead to the degradation of other objectives. It is impossible to
make all of the objectives to be optimal at the same time.
Instead, a set of solutions that represent the trade-off among
multiple objectives exist for MOPs. In addition, different types
of constraints are often unavoidable in MOPs. Such MOPs
with constraints are usually termed multi-objective constrained
optimization problem. Constraints can be roughly divided into
two categories, equality and inequality constraints. Without
loss of generality, a multi-objective constrained optimization
problem can be defined as follows:
minimize F (x) = (f
1
(x), . . . , f
m
(x)) (1)
subject to g
i
(x) ≥ 0, i = 1, . . . , q
subject to h
j
(x) = 0, j = 1, . . . , p
Where x = (x
1
, x
2
, . . . , x
n
) ⊂ R
n
is n-dimensional design
variables,F(x) = (f
1
(x), f
2
(x), . . . , f
m
(x)) ⊂ R
m
is m-
dimensional objective vector. g
i
(x) ≥ 0 define q inequality
constraints, h
j
(x) = 0 define p equality constraints.
The existing multi-objective constrained evolutionary algo-
rithms combine the multi-objective evolutionary algorithms
with the mechanisms of constraint handling [1]. At present,
NSGA-II [2] and MOEA/D [3] are the two classical multi-
objective evolutionary algorithms representing two categories
of fitness assignment methods, namely fitness assignment
based on domination and decomposition. In fitness assignment
based on domination, the fitness is decided by non-dominated
sorting and crowding distance. Representative algorithms us-
ing this type of fitness assignment method include MOGA
[4] , PAES-II [5] , SPEA-II [6] and NSGA-II [2]. In fitness
assignment based on decomposition, comparison and sorting
of individuals are made via aggregation function with weights
allocated specifically to all individuals. Typical algorithms of
this category include IMMOGLS [7], UGA [8] , cMOGA [9]
, MOGLS [10] , and MOEA/D [3].
The existing constraints handling mechanism can be divided
into four categories. They are feasibility maintenance, penalty
function, separation of constraint violation and objective value,
and multi-objective evolutionary algorithms (MOEAs). The
methods of feasibility maintenance are usually applied to the
discrete optimization problems, such as the job shop schedul-
ing problems and the vehicle routing problems. They either
design appropriate coding and decoding methods to ensure
that the individuals are feasible, or apply some mechanisms
to repair the infeasible individuals. Unlike the feasibility main-
tenance methods, the penalty function method is adding one
penalty term to the objective functions and transforming the
constrained optimization problem into an unconstrained one.
Typical methods of this category include segregated penalty
functions [17], death penalty functions [18], co-evolutionary
penalty functions [19] and adaptive penalty functions [20,21].