Layer-wise Lipschitz-Product Control for Deep Kolmogorov--Arnold Network Representations of Compositionally Structured Functions

arXiv cs.LG / 4/30/2026

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Key Points

  • The paper shows that any continuous function on [0,1]^n representable by a finite computation tree with compositional sparsity s=O(1) can be expressed using a deep Kolmogorov–Arnold Network (KAN) with controlled internal block structure.
  • It introduces layer-wise Lipschitz-product control via primitive KAN blocks with bounded block depth, yielding a primary domain-sensitive bound that is independent of the input dimension n.
  • For common compositional operations (+, −, ×, sin, cos) with bounded inputs, the Lipschitz product bound simplifies to P(KAN) <= 1, and the paper provides associated layer-width and range bound estimates.
  • The authors derive uniform approximation error bounds and show that, for sufficiently smooth functions (f in C^m), the KAN approximation achieves optimal B-spline convergence rates.
  • Experiments corroborate the theoretical claims, reporting P(KAN)=1.0 on several compositionally structured benchmark functions and addressing a previously noted gap in Lipschitz control for deep KAN stacks.

Abstract

We prove that any continuous function f from [0,1]^n to R representable by a finite computation tree with N internal nodes and compositional sparsity s = O(1) admits a deep Kolmogorov-Arnold Network (KAN) representation. Each internal node is realised by a primitive KAN block with controlled block depth and Lipschitz product. The layer-wise Lipschitz product satisfies the primary domain-sensitive bound independent of the input dimension n. It simplifies to P(KAN_f) <= max(C*,1)^L_f with L_f <= c_max * N. For the standard operations {+,-,x,sin,cos} with x nodes on [0,1]-bounded inputs we obtain P(KAN) <= 1. Layer widths satisfy n_l <= n + 2 w_max * N. The uniform approximation error is bounded by N * max(C*,1)^d(f) * epsilon_Op (simplifies when C* <=1). For f in C^m we obtain optimal B-spline rates. Range bounds are also derived (B_f <= N+1 for additive trees). This addresses the gap on Lipschitz control in deep KAN stacks noted by Liu et al. (2024). Experiments confirm P(KAN)=1.0 for several compositionally structured functions.