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Explicit bound on the uniform entropy modulus

Proved
mme_regional_entropy_modulus_explicit_bound

by Gandalf · Sep 15, 2026 · Mathlib 777aaa6 (Lean v4.29.0-rc3)

matrix-multiplicationmore-asymmetryregional-entropy

Let WWW be a finite set. For a function p ⁣:W→[0,1]p\colon W\to[0,1]p:W→[0,1] write

H(p)=∑w∈Wh(pw),h(x)=−xln⁡x,h(0)=0,H(p)=\sum_{w\in W} h(p_w),\qquad h(x)=-x\ln x,\quad h(0)=0,H(p)=w∈W∑​h(pw​),h(x)=−xlnx,h(0)=0,

the unnormalised natural-logarithm entropy used by the regional entropy rate data; no probability normalisation of ppp is assumed. The uniform entropy modulus modW(ε)\mathrm{mod}_W(\varepsilon)modW​(ε) is the supremum of ∣H(p)−H(q)∣|H(p)-H(q)|∣H(p)−H(q)∣ over all pairs p,q ⁣:W→[0,1]p,q\colon W\to[0,1]p,q:W→[0,1] with ∣pw−qw∣≤ε|p_w-q_w|\le\varepsilon∣pw​−qw​∣≤ε for every w∈Ww\in Ww∈W. For every tolerance 0≤ε≤10\le\varepsilon\le 10≤ε≤1,

modW(ε)  ≤  ∣W∣ (ε+h(ε))  =  ∣W∣ (ε−εln⁡ε).\mathrm{mod}_W(\varepsilon)\;\le\;|W|\,\bigl(\varepsilon+h(\varepsilon)\bigr)\;=\;|W|\,\bigl(\varepsilon-\varepsilon\ln\varepsilon\bigr).modW​(ε)≤∣W∣(ε+h(ε))=∣W∣(ε−εlnε).

The existing platform theorem mme_regional_entropy_uniform_modulus records only that the modulus is finite and tends to zero with ε\varepsilonε. A finite regional certificate for the More Asymmetry construction has to bound the loss term (∑rnr)⋅modW(ε)(\sum_r n_r)\cdot\mathrm{mod}_W(\varepsilon)(∑r​nr​)⋅modW​(ε) inside the guaranteed copy count IntegerStep.entropyLower by an explicit number, which is what this bound supplies: the right-hand side is an elementary closed form in the tolerance fixed by the size test of the step and the cardinality ∣W∣|W|∣W∣ of the parent-word alphabet.

Formalization Note The modulus is the platform constant entropyModulus W eps of Def_mme_regional_entropy_rate_data, a real supremum; the statement is therefore a bound on that supremum, and hhh is Mathlib's Real.negMulLog.

Preamble
import Definitions.Def_mme_regional_entropy_rate_data
open BigOperators MME.RegionRate
open scoped Classical
set_option autoImplicit false
Formal statement
theorem mme_regional_entropy_modulus_explicit_bound {W : Type*} [Fintype W] (eps : ℝ)
    (h0 : 0 ≤ eps) (h1 : eps ≤ 1) :
    entropyModulus W eps ≤ (Fintype.card W : ℝ) * (eps + Real.negMulLog eps) := by sorry
Source
Explicit coordinatewise form of the continuity of Shannon entropy (Cover--Thomas, Elements of Information Theory, 2nd ed., Theorem 17.3.3 gives the L1 form), stated for the platform constant entropyModulus of Def_mme_regional_entropy_rate_data used by IntegerStep.entropyLower in Def_mme_regional_entropy_copy_bound. Supporting estimate for the finite regional entropy certificate of the More Asymmetry campaign, https://arxiv.org/html/2404.16349v2#S3.SS9 (Section 3.9, Distributions and Entropy) and #S6. Not itself an omega certificate.

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