  The dynamics of Boolean networks (the N-K model) with scale-free topology are
studied here. The existence of a phase transition governed by the value of the
scale-free exponent of the network is shown analytically by analyzing the
overlap between two distinct trajectories. The phase diagram shows that the
phase transition occurs for values of the scale-free exponent in the open
interval (2,2.5). Since the Boolean networks under study are directed graphs,
the scale-free topology of the input connections and that of the output
connections are studied separately. Ultimately these two topologies are shown
to be equivalent. An important result of this work is that the fine-tuning
usually required to achieve stability in Boolean networks with a totally random
topology is no longer necessary when the network topology is scale-free.
