A note on two-dimensional linear discriminant analysis

2DLDA and its variants have attracted much attention from researchers recently due to the advantages over the singularity problem and the computational cost. In this paper, we further analyze the 2DLDA method and derive the upper bound of its criterion. Based on this upper bound, we show that the discriminant power of two-dimensional discriminant analysis is not stronger than that of LDA under the assumption that the same dimensionality is considered. In experimental parts, on one hand, we confirm the validity of our claim and show the matrix-based methods are not always better than vector-based methods in the small sample size problem; on the other hand, we compare several distance measures when the feature matrices and feature vectors are applied. The matlab codes used in this paper are available at http://www.mathworks.com/matlabcentral/fileexchange/loadCategory.do?objectType=category&objectId=127&objectName=Application.