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PhyslibAlpha.ProbabilisticTheory.JordanOrderUnit.JB.GeneratedByOne.Closed

The closed subalgebra generated by one observable

i. Overview

The closure `C(a)` of the subalgebra generated by `1` and `a` in a JB-algebra is closed under the Jordan product, because the product is continuous. It is complete, and associative since the subalgebra generated by one element is. So `C(a)` is a commutative real Banach algebra.

ii. Key results

  • `NormedJordanAlgebra.closedGeneratedByOne` : the closed subalgebra generated by `a`.
  • `NormedJordanAlgebra.mul_mem_closedGeneratedByOne` : it is closed under the Jordan product.
  • `NormedJordanAlgebra.assoc_of_mem_closedGeneratedByOne` : the product is associative on it.
  • `NormedJordanAlgebra.ClosedGeneratedByOne` : it as a commutative normed algebra.

iii. Table of contents

  • A. The closure
  • B. Closure under the Jordan product
  • C. Completeness
  • D. The bundled commutative normed algebra

A. The closure

B. Closure under the Jordan product

C. Completeness

D. The bundled commutative normed algebra

19 declarations

definition

Closed Jordan subalgebra CJ(a)C_J(a) generated by 11 and aa

For an element aa in a normed Jordan algebra EE over R\mathbb{R}, this definition defines CJ(a)C_J(a) as the topological closure of the R\mathbb{R}-submodule J[a]J[a] generated by the identity element 11 and aa. The submodule J[a]J[a] is the span of the set of Jordan powers {an}n∈N\{a^n\}_{n \in \mathbb{N}}, where a0=1a^0 = 1.

theorem

J[a]⊆CJ(a)J[a] \subseteq C_J(a)

For any element aa in a normed Jordan algebra EE over R\mathbb{R}, the R\mathbb{R}-submodule J[a]J[a] generated by the Jordan powers {an}n∈N\{a^n\}_{n \in \mathbb{N}} (where a0=1a^0 = 1) is contained within its topological closure CJ(a)C_J(a).

theorem

1∈CJ(a)1 \in C_J(a)

For any element aa in a normed Jordan algebra EE, the identity element 11 belongs to the closed Jordan subalgebra CJ(a)C_J(a) generated by 11 and aa.

theorem

a∈CJ(a)a \in C_J(a)

For any element aa in a normed Jordan algebra EE, aa is an element of the closed Jordan subalgebra CJ(a)C_J(a) generated by the identity element 11 and aa.

theorem

CJ(a)C_J(a) is Closed under the Jordan Product

Let EE be a normed Jordan algebra. For any element a∈Ea \in E, let CJ(a)C_J(a) denote the topological closure of the subalgebra generated by the identity element 11 and aa. For any elements x,y∈Ex, y \in E, if x∈CJ(a)x \in C_J(a) and y∈CJ(a)y \in C_J(a), then their Jordan product x⋅yx \cdot y is also an element of CJ(a)C_J(a).

theorem

The Jordan product is associative on CJ(a)C_J(a)

Let EE be a normed Jordan algebra and aa be an element in EE. Let CJ(a)C_J(a) denote the closed R\mathbb{R}-submodule generated by the identity element 11 and aa, which is the topological closure of the span of the Jordan powers {an}n∈N\{a^n\}_{n \in \mathbb{N}}. For any elements x,y,z∈CJ(a)x, y, z \in C_J(a), the Jordan product is associative, satisfying (x∗y)∗z=x∗(y∗z)(x * y) * z = x * (y * z).

theorem

CJ(a)C_J(a) is a closed set

Let EE be a normed Jordan algebra and let a∈Ea \in E. The set CJ(a)C_J(a), defined as the topological closure of the R\mathbb{R}-submodule generated by the identity element 11 and the element aa (the span of the Jordan powers {an}n∈N\{a^n\}_{n \in \mathbb{N}}), is a closed set in EE.

theorem

CJ(a)C_J(a) is complete

Let EE be a normed Jordan algebra that is complete (i.e., a JB-algebra). For any element a∈Ea \in E, the subalgebra CJ(a)C_J(a)—defined as the topological closure of the R\mathbb{R}-submodule generated by the identity element 11 and aa—is complete.

abbrev

Closed Jordan subalgebra C(a)C(a) generated by 11 and aa

For an element aa in a normed Jordan algebra EE, this definition denotes the type representing the norm-closed Jordan subalgebra C(a)C(a) generated by the identity 11 and aa. Although the multiplication in the ambient algebra EE is generally non-associative, the multiplication restricted to this subtype is associative, making C(a)C(a) a commutative real Banach algebra.

instance

Multiplication on the closed Jordan subalgebra C(a)C(a)

The closed Jordan subalgebra C(a)C(a) generated by the identity 11 and an element aa is equipped with a multiplication operation. For any x,y∈C(a)x, y \in C(a), the product x⋅yx \cdot y is defined as the Jordan product inherited from the ambient normed Jordan algebra EE.

theorem

Multiplication in C(a)C(a) coincides with the Jordan product in EE

Let EE be a normed Jordan algebra and a∈Ea \in E. Let C(a)C(a) be the norm-closed Jordan subalgebra generated by the identity 11 and aa. For any elements x,y∈C(a)x, y \in C(a), the product x⋅yx \cdot y computed within C(a)C(a) is equal to the Jordan product x⋅yx \cdot y of their corresponding elements in the ambient algebra EE.

instance

Identity element 1∈C(a)1 \in C(a)

For an element aa in a normed Jordan algebra EE, the closed Jordan subalgebra C(a)C(a) generated by the identity 11 and aa is equipped with a multiplicative identity element, denoted as 11. This element corresponds to the identity element of the ambient algebra EE.

theorem

The identity element of C(a)C(a) is the identity element of EE

Let EE be a normed Jordan algebra and a∈Ea \in E. Let C(a)C(a) be the closed Jordan subalgebra generated by the identity element 11 and aa. The identity element 11 of the subalgebra C(a)C(a) is equal to the identity element 11 of the ambient algebra EE.

instance

C(a)C(a) is a commutative ring

The closed Jordan subalgebra C(a)C(a) generated by an element aa and the identity 11 in a normed Jordan algebra EE forms a commutative ring. While the Jordan product in the ambient algebra EE is generally non-associative, its restriction to C(a)C(a) is associative, satisfying (x⋅y)⋅z=x⋅(y⋅z)(x \cdot y) \cdot z = x \cdot (y \cdot z) for all x,y,z∈C(a)x, y, z \in C(a), alongside the standard axioms of a commutative ring.

instance

C(a)C(a) is an R\mathbb{R}-algebra

The closed Jordan subalgebra C(a)C(a) generated by an element aa and the identity 11 in a normed Jordan algebra EE is an algebra over the real numbers R\mathbb{R}. This algebra structure is inherited from the ambient algebra EE, where the scalar multiplication c⋅xc \cdot x for c∈Rc \in \mathbb{R} and x∈C(a)x \in C(a) is defined by the scalar multiplication in EE, and the unit map is given by c↦c⋅1c \mapsto c \cdot 1.

instance

C(a)C(a) is a normed ring

For an element aa in a normed Jordan algebra EE, the closed Jordan subalgebra C(a)C(a) generated by the identity 11 and aa forms a normed ring. The norm on C(a)C(a) is inherited from EE and is submultiplicative, satisfying ∥x⋅y∥≤∥x∥⋅∥y∥\|x \cdot y\| \le \|x\| \cdot \|y\| for all x,y∈C(a)x, y \in C(a), where the product is the restricted Jordan product.

instance

C(a)C(a) is a normed R\mathbb{R}-algebra

For an element aa in a normed Jordan algebra EE, the closed Jordan subalgebra C(a)C(a) generated by the identity 11 and aa is a normed algebra over the real numbers R\mathbb{R}. This means the R\mathbb{R}-algebra structure on C(a)C(a) is compatible with the norm inherited from EE, specifically satisfying the property ∥λ⋅x∥=∣λ∣∥x∥\|\lambda \cdot x\| = |\lambda| \|x\| for all scalars λ∈R\lambda \in \mathbb{R} and elements x∈C(a)x \in C(a).

instance

Completeness of EE implies completeness of C(a)C(a)

Let EE be a normed Jordan algebra. If EE is a complete space, then for any element a∈Ea \in E, the closed Jordan subalgebra C(a)C(a) generated by the identity 11 and aa is also a complete space.

theorem

xnx^n in C(a)C(a) Equals the nn-th Jordan Power x[n]x^{[n]} in EE

Let EE be a normed Jordan algebra and a∈Ea \in E. Let C(a)C(a) be the norm-closed Jordan subalgebra generated by 11 and aa. For any element x∈C(a)x \in C(a) and any natural number n∈Nn \in \mathbb{N}, the nn-th power of xx computed within the commutative ring structure of C(a)C(a) is equal to the nn-th Jordan power of xx computed in the ambient algebra EE. That is, xn=x[n]x^n = x^{[n]}, where x[n]x^{[n]} is defined by x[0]=1x^{[0]} = 1 and x[n+1]=x∘x[n]x^{[n+1]} = x \circ x^{[n]}.