  The in-degree and out-degree distributions of a growing network model are
determined. The in-degree is the number of incoming links to a given node (and
vice versa for out-degree. The network is built by (i) creation of new nodes
which each immediately attach to a pre-existing node, and (ii) creation of new
links between pre-existing nodes. This process naturally generates correlated
in- and out-degree distributions. When the node and link creation rates are
linear functions of node degree, these distributions exhibit distinct power-law
forms. By tuning the parameters in these rates to reasonable values, exponents
which agree with those of the web graph are obtained.
