“…Since LDA often suffers from the small sample size (3S) problem, some effective approaches have been proposed, such as PCA + LDA [35], orthogonal LDA [36], LDA/GSVD [37], and LDA/QR [38]. Because of the advantages over the singularity problem and the computational cost, 2DLDA and its variants have recently attracted much attention from researchers (e.g., [39,40,41,42,43,44]). With applying the label information, the LDA-like methods are intend to compute the discriminant vectors which maximize the ratio of the between-class distance to the within-class distance.…”