  Experimental results often do not assess network structure; rather, the
network structure is inferred by the dynamics of the nodes. From the dynamics
of the nodes one then constructs a network of functional relations, termed the
functional network. A fundamental question in the analysis of complex systems
concerns the relation between functional and structural networks. Using
synchronisation as a paradigm for network functionality, we study the dynamics
of cluster formation in functional networks. We show that the functional
network can drastically differ from the structural network. We uncover the
mechanism driving these bifurcations by obtaining necessary conditions for
modular synchronisation.
