the optimal values of regularization parameter γ and radial basis kernel
width parameter σ. The common selection method is the cross valida-
tion method, but this method will not only consume a lot of computing
time, but also take on certain blindness. So the proposed CPSO algorithm
with global optimization ability is used to optimize the parameters of
LS-SVM model. This can not only overcome the time-consuming and
blindness of the cross validation method, but also reflect small sample
learning ability, so as to improve the learning performance, generaliza-
tion ability and robustness. Finally, a new data classificat ion method
based on the CPSO algorithm and LS-SVM model (CPL-SVM) is proposed
in this paper. The binary classification data, IRIS flower data and three
relevant data sets with pharmacodynamic properties of drug are select-
ed to verify the effectiveness of the proposed CPL-SVM method.
The rest of this paper is organized as follows. Section 2 briefly intro-
duces the related works about SVM, LS-SVM and their improve d
methods in the classification. Section 3 briefly introduces the related
basic methods, including the COA, PSO algorithm, LS-SVM model and
diversity-guided mutation strategy. Section 4 presents a chaotic particle
swarm optimization algorithm, named the CPSO algorithm. Section 5
presents a novel data classification (CPL-SVM) method. In this section,
the thoughts, model and the steps of the CPL-SVM method are intro-
duced in detail. Section 6 applies and analyzes the CPL-SVM method
in solving data classifi cation problem. Finally, the conclusions are
discussed in Section 7.
2. Related works
In recent years, in allusion to the optimization parameters of the
SVM model or LS-SVM model, many researchers have deeply studied
and explored from the different views in optimizing these parameters.
They have proposed some optimization methods of parameters of the
SVM model or LS-SVM model, such as empirical selection method, gra-
dient descent method, cross validation method, GA, PSO algorithm and
so on [4–8].Temkoaetal.[9] proposed a fuzzy integral based combining
different information sources to classify a small set of highly confusable
human non-speech sounds. Devos et al. [10] proposed a methodological
approach to guide the optimization parameters of SVM based on a grid
search f or minimizing the classification error rate . Tao et al. [11]
proposed a new fast pruning algorithm for chemical pattern classifica-
tion. Ghorbanzad'e and Fatemi [12] proposed a classification method
of central nervous syste m agents by using LS-SVM based on their
structural descriptors. Li et al. [13] proposed a novel automatic speaker
age and gender identification approach based on combin ing seven
different m ethods in order to improve the baseline performance.
Huang et al. [14] proposed an informative novel tree kernel SVM classi-
fier to model the relationship between bioacti vity and molecular
descriptors. Dong and Luo
[15] p
roposed a new method to achieve bear-
ing
degradation classi fication based on principal component analysis
(PCA) and optimized LS-SVM method. Lou'i et al. [16] proposed two
new multisensor data fusion algorithms to reduce the rate of false
detection and obtain reliable decisions on the presence of target objects.
Zhang [17] proposed an improved data classification method based on
SVM applying rational sample data selection and GA-controlled training
parameters optimization. Yao and Yi [18] proposed a new License Plate
(LP) detection technique based on multistage information fusion. Sung
and Chung [19] proposed a distributed energy monitoring network
system based on da ta fusion via improved PSO algorithm. He et al.
[20] proposed a new method for classifying electronic nose data in
rats wound infection detection based on SVM an d wavelet analysis.
Subha jit et al. [21] proposed a PSO method al ong with adaptive K-
nearest neighborhood based gene selection technique to distinguish a
small subset of useful genes.
For the optimization parameters of SVM model and LS-SVM model,
although these scholars have done the in-depth study and discussion
by using the various optimization methods from the different angle
degree in order to obtain some good results, each proposed method
has its own defect in optimizing parameters of SVM model and LS-
SVM model, such as the low classification accuracy, weak generalization
ability, slow convergence speed, and so on. So the CPSO algorithm based
on COA and PSO is proposed to select and optimize the parameters of
LS-SVM model in order to improve the classification accuracy, learning
performance and generalization ability.
3. Basic methods
3.1. Chaotic optimization algorithm (COA)
Chaos often exists in the nonlinear system. It is a kind of characteris-
tic that has a bounded unstable dynamic behavior and exhibits sensitive
dependence on the initial conditions. Chaotic optimization algorithm
(COA) [22] is a population-based stochastic optimization algorithm by
using the chaotic mapping. The basic procedure of the COA is divided
into two steps. First, the COA searches all the points in turn within the
changing range of variables, and selects the better point as the current
optimum point by using chaotic ergodicity, regularity, initial sensitivity
and topological transitivity. Then the current optimum point is regarded
as the center, a tiny chaotic disturbance is imposed and a careful search
is performed in order to find out the global optimum point with the
higher probability. Due to the chaotic non-repetition, the COA can
carry out the overall search with the higher speed. So the COA takes
on the characteristics of the easy implementation, short execution
time and robust mechanism.
Currently, there have been several kinds of the COA based on chaotic
characteristics, such as adaptive mutative scale COA [23], a mutative
scale COA [24], chaotic harmony search algorithm [25], multi-objective
chaotic ant swarm optimization [26] and so on. Because the adaptive
mutative scale COA has the refined search space, better search speed
and higher search accuracy [23], it is used to optimize the particle
swarm optimization (PSO) algorithm in this paper. Generally, the main
problem of the COA is to obtain chaotic variables. So the Logistic chaotic
model is used to generate the chaotic variable. The mapping equation of
the Logistic model is described:
Z
nþ1
¼ L μ; X
n
ðÞ
¼ μZ
n
1−X
n
ðÞ
μ ∈ 0 ; 4
½
; n ¼ 0 ; 1; 2; 3; ⋯ ð1Þ
where control variable (μ ∈ [0, 4]) is the parameter of the Logistic. It has
shown, when Z
n
∈ [0, 1], the Logistic mapping is in the chaotic state. That
is, the generated sequences under Logistic mapping function (the initial
condition Z
0
) are not periodic and conve rge. But the generated
sequences must converge to one specific value outside the given range.
3.2. Particle swarm optimization (PSO)
The PSO algorithm [27] is a search algorithm based on simulating the
social behavior of birds within a flock. In the PSO algorithm, individuals,
referred to as particles, are “flown” through hyper dimensional search
space. The positions of particles within the search space are changed
based on the social-psychological tendency of individuals in order to
delete the success of other individuals. The changing of particle within
the population is influenced by the expe rience, or knowledge. The
consequenc e of modeling for the social behavior is that the search is
processed in order to return toward previously successful regions in
the search space. Namely, the velocity (v) and position (x) of each
particle will be changed according to the following expressions:
v
ij
t þ 1ðÞ¼wv
ij
tðÞþc
1
r
1
pB
ij
tðÞ−x
ij
tðÞ
þ c
2
r
2
gB
ij
tðÞ−x
ij
tðÞ
ð2Þ
x
ij
t þ 1ðÞ¼x
ij
tðÞþv
ij
t þ 1ðÞ ð3Þ
where v
ij
(t + 1) is the velocity of particle i
th
at iteration j
th
,x
ij
(t + 1) is
the position of particle i
th
at iteration j
th
. w is inertia weight to be
employed to control the impact of the velocity of previous histo ry.
148 F. Liu, Z. Zhou / Chemometrics and Intelligent Laboratory Systems 147 (2015) 147–156