Sharp Reconstruction Bounds for Autoencoders Using the Same Forward Map
Abstract
We study reconstruction in autoencoders that apply the same forward map before and after setting the observed coordinates to zero. For equal odd input and hidden dimensions d≥ 3, among orientation-preserving diffeomorphisms whose Jacobian singular values lie in [m,M], we show that the least uniform reconstruction-derivative error is max{1−M(M−m)/2,0}, with affine maps attaining this sharp bound at every prescribed depth. A translated radial rotation can nevertheless reconstruct any prescribed ball exactly with singular values arbitrarily close to one, motivating additional conditions for a finite-data bound. We test this prediction on a 798,452-point terrestrial LiDAR forest scan. At input scale $0.05$, the mean theoretical bound is $0.155$, about 84% of the mean normalized training error $0.185$ across four spatial regions, two depths, and three seeds. At this scale, adding one hidden coordinate reduces the mean reconstruction error below 6×10−6.
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BibTeX
@misc{medina2026sharp,
title = {{Sharp Reconstruction Bounds for Autoencoders Using the Same Forward Map}},
author = {Patricia Medina and Hy P. G. Lam},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.20333},
eprint = {2609.20333},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.20333},
}
RIS
TY - UNPB
TI - Sharp Reconstruction Bounds for Autoencoders Using the Same Forward Map
AU - Patricia Medina
AU - Hy P. G. Lam
PY - 2026
DA - 2026/09/17
PB - arXiv
DO - 10.48550/arxiv.2609.20333
UR - https://arxiv.org/abs/2609.20333
AB - We study reconstruction in autoencoders that apply the same forward map before and after setting the observed coordinates to zero. For equal odd input and hidden dimensions d≥ 3, among orientation-preserving diffeomorphisms whose Jacobian singular values lie in [m,M], we show that the least uniform reconstruction-derivative error is max{1−M(M−m)/2,0}, with affine maps attaining this sharp bound at every prescribed depth. A translated radial rotation can nevertheless reconstruct any prescribed ball exactly with singular values arbitrarily close to one, motivating additional conditions for a finite-data bound. We test this prediction on a 798,452-point terrestrial LiDAR forest scan. At input scale $0.05$, the mean theoretical bound is $0.155$, about 84% of the mean normalized training error $0.185$ across four spatial regions, two depths, and three seeds. At this scale, adding one hidden coordinate reduces the mean reconstruction error below 6×10^−6.
ER -