Figure 3. Modularity of matrices and their corresponding networks.

The NxN matrix A can be represented as a directed network of weighted interactions between the inputs and the outputs (with 2N nodes). Modularity is measured using normalized measure of community structure of the interaction network, Q_m (see Text S1) [18]. (A) Examples of two modular matrices and their corresponding modularity measure Q_m. Modular matrices typically show Q_m>0.2, with a maximal value of Q_m = 1 for a diagonal matrix. (B) An example of a non-modular matrix. Non-modular matrices have Q_m around 0.