Gene expression analysis is the use of quantitative RNA measurements of gene expression in order to characterize biological processes and clarify the mechanisms of gene transcription. The microarray technology makes it possible to monitor the expression levels of tens of thousands of genes in parallel. It measures the relative RNA levels of genes and produces high dimensional dataset, which is in turn a highly informative source for gene expression analysis. The microarray data from a series of N experiments may be represented as N×M gene expression matrix in which each of the N rows consists of an M-element expression vector. The latter vector represents the gene expression level of the genes for a single experiment.
Table 1 displays an example matrix for gene expression data, where the rows denote different samples or conditions (such as the same cell type among different samples), while the columns denote genes; F [Sample 3, G4] denotes the quantitative expression of gene G4 in Sample 3.