Jensen's inequality on parity classes of jump M-convex functions
Abstract
We prove Jensen's inequality on each coordinatewise parity class of a jump M-convex function on ℤn, without assuming strong base orderability or a finite effective domain. If a finite convex combination of domain points has its barycenter in the same parity class, then the barycenter belongs to the domain and satisfies Jensen's inequality. We also prove that every domain point admits an affine support on its entire parity class. The set of support vectors is characterized by at most 3n−1 local inequalities, which yield optimality certificates, attained duality, and an exact formula for linear growth and stability under linear perturbations. The same conclusions hold for distributions with finite first moment supported on domain points of a single parity class, provided their mean lies in that class. We characterize equality by contact sets and give a quantitative bound on the Jensen gap. The proof combines induction on dimension with the known closure under infimal convolution: convolution with an even-box indicator gives finite-domain supports, a quadratic kernel proves barycenter feasibility, and a fixed local kernel yields global supports. A two-dimensional example shows that total parity alone does not suffice.
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BibTeX
@misc{liu2026jensens,
title = {{Jensen's inequality on parity classes of jump M-convex functions}},
author = {Xinyue Liu},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.13965},
eprint = {2610.13965},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.13965},
}
RIS
TY - UNPB
TI - Jensen's inequality on parity classes of jump M-convex functions
AU - Xinyue Liu
PY - 2026
DA - 2026/10/01
PB - arXiv
DO - 10.48550/arxiv.2610.13965
UR - https://arxiv.org/abs/2610.13965
AB - We prove Jensen's inequality on each coordinatewise parity class of a jump M-convex function on ℤ^n, without assuming strong base orderability or a finite effective domain. If a finite convex combination of domain points has its barycenter in the same parity class, then the barycenter belongs to the domain and satisfies Jensen's inequality. We also prove that every domain point admits an affine support on its entire parity class. The set of support vectors is characterized by at most 3^n−1 local inequalities, which yield optimality certificates, attained duality, and an exact formula for linear growth and stability under linear perturbations. The same conclusions hold for distributions with finite first moment supported on domain points of a single parity class, provided their mean lies in that class. We characterize equality by contact sets and give a quantitative bound on the Jensen gap. The proof combines induction on dimension with the known closure under infimal convolution: convolution with an even-box indicator gives finite-domain supports, a quadratic kernel proves barycenter feasibility, and a fixed local kernel yields global supports. A two-dimensional example shows that total parity alone does not suffice.
ER -