Most real networks exhibit the presence of non trivial correlations in their connectivity pattern. Indeed, empirical measurements bring evidence to the fact that, in some instances, high or low degree vertices of the network tend to preferentially connect to other vertices with similar degree. In this situa- tion, correlations are named assortative and are typically observed in social networks. On the other hand, connections in many technological and biological networks attach vertices of very different degree with stronger likelihood. Correlations are in this case referred to as disassortative. The overall origin of the appearance of these correlations is not yet completely understood, neither is the reason for the distinction in real systems between assortative and disassortative behavior.