Maximum margin criterion with tensor representation
Rong-Xiang Hu
a,b
, Wei Jia
a,
, De-Shuang Huang
a
, Ying-Ke Lei
a,b,c
a
Hefei Institute of Intelligent Machines, Chinese Academy of Science, PO Box 1130, Hefei 230031, China
b
Department of Automation, University of Science and Technology of China, Hefei 230027, China
c
Department of Information, Electronic Engineering Institute, Hefei 230037, China
article info
Keywords:
Tensor representation
Maximum Margin Criterion
Subspace learning
abstract
In this paper, we propose tensor based Maximum Margin Criterion algorithm (TMMC) for supervised
dimensionality reduction. In TMMC, an image object is encoded as an nth-order tensor, and its 2-D
representation is directly treated as matrix. Meanwhile, the k-mode optimization approach is exploited
to iteratively learn multiple interrelated discriminative subspaces for dimensionality reduction of the
higher order tensor. TMMC generalizes the tradition al MMC based on vector data to the one based on
matrix and tensor data, which completes the MMC family in terms of data representation. The results of
experiments conducted on four databases show that the accurate recognition rate of TMMC is better
than that of the method of Concurrent Subspaces Analysis (CSA), and is comparable with the method of
Multilinear Discriminant Analysis (MDA). The experimental results also show that the accurate
recognition rate of the tensor/matrix-based methods may not always be better than that of vector-
based methods. Reasonable discussions about this phenomenon have been given in this paper.
& 2010 Elsevier B.V. All rights reserved.
1. Introduction
In recent years, the research on dimensionality reduction
[1,2,19,20,29,30] is very active, and many algorithms of dimen-
sionality reduction are mainly utilized for image recognition.
Particularly, in the past decade, these algorithms have been
through a series of changes in the representation of data. In the
early stage of the research in this field, almost all representative
algorithms including Principal Component Analysis (PCA) [1] and
Linear Discriminant Analysis (LDA) [2] require that the 2-D image
data must be reshaped into 1-D vector, which can be referred to as
the strategy of ‘‘image-as-vector’’. However, the operation of
vectorization inevitably leads to two obvious disadvantages.
Firstly, it usually causes the ‘‘curse of dimensionality’’ dilemma
and ‘‘small sample size’’ problem. Secondly, it might break the
intrinsic 2-D structure of an image matrix, which results in the
failure of exploration of spatial/correlation information. Thus,
there is an increasing demand for uncovering the underlying
structures in different data representations to enhance the
performance of dimensionality reduction algorithms. With the
development of research, it is believed that, in the real world, an
object often has some specialized structures and such structures
are intrinsically in the form of second or even higher order tensor.
In this regard, vector is the first-order tensor and matrix is the
second-order tensor.
When vector based PCA and LDA were extended to matrix
based PCA and LDA [3–11], this strategy is called as ‘‘image-as-
matrix’’. Generally, the matrix-based algorithms have two models,
which are unilateral projection and bilateral projection, respec-
tively. Additionally, the former can be considered as a special case
of the latter.
Yang et al. [3] proposed 2DPCA, which only used one
projection matrix to conduct dimensionality reduction with a 2-
D matrix representation, referred to as unilateral projection. Later,
Xu et al. [4] proposed Coupled Subspace Analysis (Xu et al. called
it as CSA-2), in which there are two projection matrices operating
on both sides of the image matrix, referred to as bilateral
projection. Ye [5] proposed Generalized Low Rank Approxima-
tions of Matrices (GLRAM), which is nearly identical to CSA-2.
Kong et al. [6] proposed Bilateral 2DPCA (B2DPCA), which is the
generalized version of 2DPCA by bilateral projection. In [7],
TensorPCA (TPCA) was proposed by Cai et al. However, although
the word ‘tensor’ was adopted, TPCA only exploited the
representation of matrix. And, it belongs to the model of bilateral
projection. Generally speaking, all of the methods introduced in
this paragraph could be regarded as the extended PCA based on
the strategy of ‘‘image-as-matrix’’.
After Yang’s 2DPCA was proposed, Kong et al. [8] proposed 2D
Fisher discriminant analysis (2DFDA), and Li and Yuan [9]
proposed 2DLDA [9] (we call it as 2DLDA1), both of which have
similar strategy with 2DPCA, and belong to the model of unilateral
projection. Later, Ye et al. [10] proposed another form of 2DLDA
(we call it as 2DLDA2), which simultaneously computed two
subspaces. TensorLDA (TLDA) proposed by Cai et al., utilized the
ARTICLE IN PRESS
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journal homepage: www.elsevier.com/locate/neucom
Neurocomputing
0925-2312/$ - see front matter & 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.neucom.2009.11.036
Corresponding author at: Hefei Institute of Intelligent Machines, Chinese
Academy of Science, PO Box 1130, Hefei 230031, China.
E-mail address: icg.jiawei@gmail.com (W. Jia).
Neurocomputing 73 (2010) 1541–1549