Automorphic Nelson Dilations for Contractions and Invariant Subspace Tracking

arXiv:2607.14372 2026 Dynamics 1 ideas extracted · analyzed Aug 30, 2026

What the math gives to ML

The paper constructs an analytic matrix-valued lift of a strict contraction by replacing each singular value with a disk automorphism. The transferable asset is a stable rational filter that agrees with the original matrix at z=0, is contractive inside the disk, and is unitary on the unit circle. This suggests recurrent and state-space neural layers with tunable memory and explicit non-expansive frequency behavior, avoiding exploding hidden dynamics without forcing the transition matrix itself to be unitary.

Ideas from this paper

Unverified 2026

Automorphic All-Pass Recurrent Layer

Parameterize a recurrent or state-space layer by a matrix-valued Blaschke lift instead of an unconstrained transition matrix. The resulting causal filter is contractive for inputs inside the unit disk and energy-preserving on the unit circle, while its value at z=0 is a freely learned strict contraction.

Useful6/10
Difficulty5/10
Novelty7/10
Paper: Automorphic Nelson Dilations for Contractions and Invariant Subspace Tracking arXiv:2607.14372