Growing Random Networks with Fitness

Abstract

Three models of growing random networks with fitness dependent growth rates are analysed using the rate equations for the distribution of their connectivities. In the first model (A), a network is built by connecting incoming nodes to nodes of connectivity $k$ and random additive fitness $η$, with rate $(k-1)+ η$. For $η>0$ we find the connectivity distribution is power law with exponent $γ=<η>+2$. In the second model (B), the network is built by connecting nodes to nodes of connectivity $k$, random additive fitness $η$ and random multiplicative fitness $ζ$ with rate $ζ(k-1)+η$. This model also has a power law connectivity distribution, but with an exponent which depends on the multiplicative fitness at each node. In the third model (C), a directed graph is considered and is built by the addition of nodes and the creation of links. A node with fitness $(α, β)$, $i$ incoming links and $j$ outgoing links gains a new incoming link with rate $α(i+1)$, and a new outgoing link with rate $β(j+1)$. The distributions of the number of incoming and outgoing links both scale as power laws, with inverse logarithmic corrections.