Degree-$M$ Bethe and Sinkhorn Permanent Based Bounds on the Permanent of a Non-negative Matrix
Yuwen Huang, Navin Kashyap, Pascal O. Vontobel
TL;DR
This work establishes degree-M Bethe- and degree-M scaled Sinkhorn-permanent-based lower and upper bounds on the permanent of a non-negative matrix, resolving a conjecture of Vontobel. By representing the permanent via an S-NFG and analyzing its M-cover lifts, the authors derive coefficient recursions C_{M,n}(γ), C_{B,M,n}(γ), and C_{scS,M,n}(γ) that express (perm(Θ))^M, (perm_B,M(Θ))^M, and (perm_scS,M(Θ))^M as sums over Γ_{M,n}, and prove explicit inequalities bounding the ratios of these coefficients. They further show asymptotic characterizations of the coefficients through entropy-like functions H'_G, H_B, and H_scS, and demonstrate that the degree-M quantities converge to the classic Bethe and Sinkhorn bounds as M→∞. The paper also provides a concrete M=2 result linking perm/perm_B,2 to pairwise permutation statistics and outlines open problems for elementary proofs, bound tightening, and generalization to broader S-NFG classes. Overall, the work deepens the combinatorial understanding of Bethe and Sinkhorn approximations for the matrix permanent and offers a rigorous path from finite-M covers to known limiting bounds.
Abstract
The permanent of a non-negative square matrix can be well approximated by finding the minimum of the Bethe free energy functions associated with some suitably defined factor graph; the resulting approximation to the permanent is called the Bethe permanent. Vontobel gave a combinatorial characterization of the Bethe permanent via degree-$M$ Bethe permanents, which are based on degree-$M$ covers of the underlying factor graph. In this paper, we prove a degree-$M$-Bethe-permanent-based lower bound on the permanent of a non-negative matrix, which solves a conjecture proposed by Vontobel in [IEEE Trans. Inf. Theory, Mar. 2013]. We also prove a degree-$M$-Bethe-permanent-based upper bound on the permanent of a non-negative matrix. In the limit $M \to \infty$, these lower and upper bounds yield known Bethe-permanent-based lower and upper bounds on the permanent of a non-negative matrix. Moreover, we prove similar results for an approximation to the permanent known as the (scaled) Sinkhorn permanent.
