Figure 4.

The SRC-AL schematic for a two-class problem, where x₁ and x₂ represent the samples of class 1 and class 2, respectively, and y is the unlabeled sample. Due to the limited space, only two labeled samples are drawn in the figure. In fact, all labeled samples are used for dictionary learning. D_up' and D_lw' represent the upper and lower parts of the learned dictionary. α_x1, α_x2, and α_y are the sparse representations of x₁, x₂, and y where the black-filled blocks represent nonzero elements.