Before revision:  Unfortunately, deriving models accurate enough to be used for control is extremely difficult, especially for large networks of nonlinearly coupled nodes. However , system responses to perturbations are often easily measured.
After revision:  Most approaches to control nonlinearly coupled systems require the network topology and/or network dynamics. Unfortunately, neither the full set of participating nodes nor the network topology is known for many important systems. On the other hand , system responses to perturbations are often easily measured.