Power laws of the in-degree and out-degree distributions of complex networks

A model for directed networks is proposed and power laws for their in-degree and/or out-degree distributions are derived from the model. It is based on the Barabasi-Albert model and contains two parameters. The parameters serve as regulatory factors for the contributions of new nodes through in- and out-degrees. The model allows a newly added link to connect directly two nodes already present in the network. Such a link is called an inner link, while a link attached to a new node is called an outer link. Using relationships between inner and outer links, we investigate power laws for in- and out-degree distributions of directed networks. This model enables us to predict some interesting features of directed networks; in particular, the World Wide Web and the networks of citation and phone-call.