Universal approximations of permutation invariant/equivariant functions by deep neural networks
Authors: Akiyoshi Sannai, Yuuki Takai, Matthieu Cordonnier
Keywords: finite group, invariant, equivariant, neural networks
TL;DR: For a given $G$-invariant/equivariant function, we construct its universal approximator by deep neural network whose layers equip $G$-actions and each affine transformations are $G$-equivariant/invariant. 
Abstract: In this paper, we develop a theory about the relationship between $G$-invariant/equivariant functions and deep neural networks for finite group $G$. Especially, for a given $G$-invariant/equivariant function, we construct its universal approximator by deep neural network whose layers equip $G$-actions and each affine transformations are $G$-equivariant/invariant. Due to representation theory, we can show that this approximator has exponentially fewer free parameters than usual models.