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Synchronization for sufficiently large logarithmic density constants
PDF p. 31: Paragraph after equation (6.2)
Statement
Assume countable choice. For every fixed , there is such that, uniformly for , with probability tending to one as , the simple graph is an -expander with and satisfies the hypotheses of Theorem 1.10; hence it is globally synchronizing. Uniformity means the supremum of the failure probability over the stated interval tends to zero; it includes every varying sequence in that range.
Facts & Assumptions
The graph law, reference centered matrices, two-sided expander and global synchrony conventions are Erdős–Rényi random graph and high probability, Centered graph matrices and reference degree, Two-sided spectral expander — Definition 1.9 and Globally synchronizing graph — Definition 1.1. The uniform quantifiers are Asymptotic quantifiers and uniform parameter ranges.
The uniform norm estimate with constant is Uniform constant-two adjacency control above a large logarithmic density. The simultaneous degree slack and numerical condition for are Uniform degree slack and the vanishing synchrony condition.
Degree slack and the adjacency norm imply the two-sided expander by Degree control implies two-sided expansion — Proposition 3.2. Its positive-reference synchrony criterion is General two-sided spectral criterion — Theorem 1.10, under The Axiom of Countable Choice (AC_ω).
For any finite family of events in one probability space, the probability of their union is at most the sum of their probabilities (The finite union bound).
Proof
Given: The objects and hypotheses in the Statement.
Goal: Prove all stated conclusions.
Choose , where is supplied by [F2]. The uniform spectral estimate persists on the smaller parameter interval with this larger lower endpoint. Intersect it with the degree good event from [F2]. By [F4] applied to the two complementary bad events, the failure probability is at most the sum of their two uniform bounds, tending to zero. On this intersection, and the exact degree inequalities of Proposition 3.2 hold. Thus [F3] establishes all three expander inequalities in the conventions of [F1].
Since , . Supplier [F2] gives , and the strict numerical condition of Theorem 1.10 uniformly for large , because . Apply [F3] under countable choice. Each graph on the good event is globally synchronizing. The probability conclusion, including every varying allowed sequence , follows from step 1.1 and the uniform quantifiers in [F1].
Source notes
The original large-density claim on PDF p. 31, after (6.2), is retained: for sufficiently large , gives , , , , the Theorem 1.10 condition and global synchrony with high probability for . The explicit range spells out its fixed small-parameter convention. The local proof preserves its rich parameter conclusion and makes the probability uniformity precise. The local proof uses Uniform constant-two adjacency control above a large logarithmic density and Uniform degree slack and the vanishing synchrony condition. The article and the fixed-law Péché–Soshnikov result are not logical suppliers for the spectral estimate.
Depends on
- Erdős–Rényi random graph and high probability
- Two-sided spectral expander — Definition 1.9
- Globally synchronizing graph — Definition 1.1
- Centered graph matrices and reference degree
- Uniform constant-two adjacency control above a large logarithmic density
- Uniform degree slack and the vanishing synchrony condition
- Degree control implies two-sided expansion — Proposition 3.2
- General two-sided spectral criterion — Theorem 1.10
- Asymptotic quantifiers and uniform parameter ranges
- The Axiom of Countable Choice (AC_ω)
- The finite union bound
Dependency tree · 2 levels
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Sources
- Expander graphs are globally synchronizing — Abdalla, Bandeira, Kassabov, Souza, Strogatz, Townsend (2026) · PDF p. 31, Paragraph after equation (6.2)