Discrimination via Principal Components

In many modern data, the number of variables is much higher than the number of observations and the within-group scatter matrix is singular. This work proposes a way to circumvent this problem by doing LDA in a low-dimensional space formed by the first few principal components (PCs) of the original data. Two approaches are considered to improve their discrimination abilities in this lowdimensional space. Specifically, the original PCs are rotated to maximize the LDA criterion, or penalized PCs are produced to achieve simultaneous dimension reduction and maximization of the LDA criterion. Both approaches are illustrated and compared on some well known data set.