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PhyslibAlpha.ProbabilisticTheory.JordanOrderUnit.JB.GeneratedByOne.Uniform

The norm of `C(a)` is uniform

i. Overview

The JB axiom `‖x²‖ = ‖x‖²` holds in `C(a)`, so `‖x^(2ⁿ)‖ = ‖x‖^(2ⁿ)` and the spectral radius is at most the norm.

ii. Key results

  • `JBAlgebra.ClosedGeneratedByOne.norm_mul_self` : `‖x²‖ = ‖x‖²`.
  • `JBAlgebra.ClosedGeneratedByOne.norm_pow_two_pow` : `‖x^(2ⁿ)‖ = ‖x‖^(2ⁿ)`.

iii. Table of contents

  • A. Uniform square norm

A. Uniform square norm

3 declarations

theorem

∥x2∥=∥x∥2\|x^2\| = \|x\|^2 in the closed Jordan subalgebra C(a)C(a)

Let aa be an element of a normed Jordan algebra, and let C(a)C(a) be the norm-closed Jordan subalgebra generated by the identity 11 and aa. For any element x∈C(a)x \in C(a), the norm of its square satisfies ∥x2∥=∥x∥2\|x^2\| = \|x\|^2.

theorem

ρ(x)≤∥x∥\rho(x) \leq \|x\| in the closed Jordan subalgebra C(a)C(a)

Let EE be a normed Jordan algebra and a∈Ea \in E. Let C(a)C(a) denote the norm-closed Jordan subalgebra generated by aa and the identity element 11. For any element x∈C(a)x \in C(a), the spectral radius of xx (with respect to the scalar field R\mathbb{R}) is less than or equal to its norm, denoted as ρ(x)≤∥x∥\rho(x) \leq \|x\|.

theorem

∥x2n∥=∥x∥2n\|x^{2^n}\| = \|x\|^{2^n} in the closed subalgebra C(a)C(a)

Let aa be an element of a normed Jordan algebra, and let C(a)C(a) be the norm-closed Jordan subalgebra generated by the identity 11 and aa. For any element x∈C(a)x \in C(a) and any natural number n∈Nn \in \mathbb{N}, the norm of the power x2nx^{2^n} satisfies the equality ∥x2n∥=∥x∥2n\|x^{2^n}\| = \|x\|^{2^n} where ∥⋅∥\|\cdot\| denotes the norm and the power is taken using the associative multiplication within C(a)C(a).