Support vector machine (SVM), as an effective method in classification problems, tries to find the optimal hyperplane that
maximizes the margin between two classes and can be obtained by solving a constrained optimization criterion using quadratic
programming (QP). This QP leads to higher computational cost. Least squares support vector machine (LS-SVM), as a variant
of SVM, tries to avoid the above shortcoming and obtain an analytical solution directly from solving a set of linear equations
instead of QP. Both SVM and LS-SVM operate directly on patterns represented by vector, i.e., before applying SVM or LS-SVM
to a pattern, any non-vector pattern such as an image has to be first vectorized into a vector pattern by some techniques
like concatenation. However, some implicit structural or local contextual information may be lost in this transformation.
Moreover, as the dimension
d of the weight vector in SVM or LS-SVM with the linear kernel is equal to the dimension
d
1 ×
d
2 of the original input pattern, as a result, the higher the dimension of a vector pattern is, the more space is needed for
storing it. In this paper, inspired by the method of feature extraction directly based on matrix patterns and the advantages
of LS-SVM, we propose a new classifier design method based on matrix patterns, called MatLSSVM, such that the new method can
not only directly operate on original matrix patterns, but also efficiently reduce memory for the weight vector (
d) from
d
1 ×
d
2 to
d
1 +
d
2. However like LS-SVM, MatLSSVM inherits LS-SVM’s existence of unclassifiable regions when extended to multi-class problems.
Thus with the fuzzy version of LS-SVM, a corresponding fuzzy version of MatLSSVM (MatFLSSVM) is further proposed to remove
unclassifiable regions effectively for multi-class problems. Experimental results on some benchmark datasets show that the
proposed method is competitive in classification performance compared to LS-SVM, fuzzy LS-SVM (FLS-SVM), more-recent MatPCA
and MatFLDA. In addition, more importantly, the idea used here has a possibility of providing a novel way of constructing
learning model.
Keywords Support vector machine (SVM) - Least squares support vector machine (LS-SVM) - Fuzzy least squares support vector machine (FLS-SVM) - Vector pattern - Matrix pattern - Pattern recognition