Figure 3: Different classes of networks classified depending on their topology. A) Random network: each node has, on average, the same number of connections. B) Small world networks: it is possible to cross all the network by a small number of steps (for instance 4 steps to go from A to B). C) Scale free network: a few nodes are mostly connected (the hubs, in yellow) than the others. D) Hierarchical network: the most connected nodes are also the most clusterized ones (the yellow ones).