Example of a good pair of genes in the colon dataset. The expression values give almost full separation between normal and tumor tissues. Along the x-axis (horizontal) are the expression values of M63391, and along the y-axis (vertical) are the expression values of H08393. The points marked 'x' are normal tissues, and the tumor tissues are marked by an 'o'. The expression values have been through the preprocessing steps described in the text. Also plotted is the DLD axis and the class-decision boundary for these two genes. Note that the DLD axis and the decision boundary are orthogonal, but as a result of different scaling on the axes it does not appear so in the plot.