Figure 1

Example of the solution space. Ranges of solutions that can be produced for each of the three variants of constraints, for an example with two genes. The red arrow represents a gene expression profile to be approximated (y). The black arrows indicate two components C₁ and C₂ (i.e. columns in C). The unconstrained variant (U) can reconstruct any point in this Gene1- Gene2 space (determined system). The P variant can only reconstruct points in the grey area, which corresponds to non-negativity of the weights for the two components. Similarly, the S variant can only reconstruct points on the line joining the two components.