Abstract

The Fisher linear discriminant analysis (LDA) is a classical method for classification and dimension reduction jointly. A major limitation of the conventional LDA is a so-called singularity issue. Many LDA variants, especially two-stage methods such as PCA+LDA and LDA/QR, were proposed to solve this issue. In the two-stage methods, an intermediate stage for dimension reduction is developed before the actual LDA method works. These two-stage methods are scalable because they are an approximate alternative of the LDA method. However, there is no theoretical analysis on how well they approximate the conventional LDA problem. In this paper we present theoretical analysis on the approximation error of a two-stage algorithm. Accordingly, we develop a new two-stage algorithm. Furthermore, we resort to a random projection approach, making our algorithm scalable. We also provide an implemention on distributed system to handle large scale problems. Our algorithm takes LDA/QR as its special case, and outperforms PCA+LDA while having a similar scalability. We also generalize our algorithm to kernel discriminant analysis, a nonlinear version of the classical LDA. Extensive experiments show that our algorithms outperform PCA+LDA and have a similar scalability with it.