Unified Universality Theorem for Deep and Shallow Joint-Group-Equivariant Machines

Sho Sonoda, Yuka Hashimoto, Isao Ishikawa, Masahiro Ikeda

Keywords: group theory, irreducible representation, universality, fully-connected network, joint-group-equivariance, ridgelet transform

TL;DR: We present a constructive universal approximation theorem for learning machines equipped with joint-group-equivariant feature maps, based on the group representation theory.

Abstract: We present a constructive universal approximation theorem for learning machines equipped with joint-group-equivariant feature maps, based on the group representation theory. ``Constructive'' here indicates that the distribution of parameters is given in a closed-form expression known as the ridgelet transform. Joint-group-equivariance encompasses a broad class of feature maps that generalize classical group-equivariance. Notably, this class includes fully-connected networks, which are *not* group-equivariant *but* are joint-group-equivariant. Moreover, our main theorem also unifies the universal approximation theorems for both shallow and deep networks. While the universality of shallow networks has been investigated in a unified manner by the ridgelet transform, the universality of deep networks has been investigated in a case-by-case manner.

Primary Area: unsupervised, self-supervised, semi-supervised, and supervised representation learning

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Submission Number: 1868