Characteristics of fraction of driver nodes (n_D) and critical edge directions as a function of 〈k〉 for the method of random direction assignment (RAD), the method based on node residual degree (NRD), the method of edge orientation for optimal controllability (EOOC) and the method of edge orientation by critical directions (EOCD) on (a, d) ER networks, (b, e) SF networks with γ = 2.5, (c, f) SF networks with γ = 3.