Symmetric group and the Axelrod model for dissemination of cultures

Abstract

We consider the model proposed by Axelrod for dissemination of cultures on a 2-dimensional squared lattice. We review this model from an analytic point of view. We define $\left\langle s(t)\right\rangle$ to quantify possible culture configurations at time $t$ in a society. Typical initial culture configurations of this model are characterised. Equation of motion in terms of $\left\langle s(t)\right\rangle$ is derived. We study the graph of development of this Axelrod system toward to its culture configurations equilibrium. Generically, we observe that this model undergoes three phases of development. We give a quantitative explanation about these three different phases of development. Keeping up with this Axelrod model, we characterize its culture configurations space at equilibrium point where $\left\langle s(t_{\text{eq}})\right\rangle = 1$. This space is called monoculture space. Understanding this space is equivalent to restrict to the space of culture configurations from one individual in the model. This individual culture space is identified to the space $V_N^{\otimes F}$ up to isomorphisms. Action of the permutation group $S_N$ on the space $V_{N}^{\otimes F}$ is considered. Under this action, the observable $\left\langle s(t)\right\rangle$ is an invariant of the Axelrod system. We explore this symmetry and classify the different inequivalent classes of culture configurations composing the monoculture space. To achieve this, we consider the case $N\geq F$. We propose techniques from group representation theory to perform this classification. The inequivalent classes of culture configurations are indexed by the Dickau diagrams which are associated to the Bell number $B_F$. A concrete example with $F=4$ and $N\geq 4$ is considered for a full illustration of our analysis.