Physlib

PhyslibAlpha.AlgebraicFramework.OrderUnit.Norm

The order-unit norm

i. Overview

`IsOrderUnit` only lets us compare outcomes to `1`; `IsArchimedeanOrderUnit` is what turns that into an actual distance. `orderUnitNorm x` is the least `r` with `-r • 1 ≤ x ≤ r • 1` — how many copies of the certain outcome it takes to sandwich `x` on both sides. This is a genuine norm, not just a seminorm, exactly because nothing is infinitesimally close to `0` without being `0`.

ii. Key definitions and results

  • `IsArchimedeanOrderUnit.orderUnitNorm`
  • `IsArchimedeanOrderUnit.orderUnitNormedAddCommGroup`

iii. Table of contents

  • A. Order-unit bounds
  • B. Norm laws
  • C. Positive definiteness
  • D. The induced normed group

A. Order-unit bounds

B. Norm laws

C. Positive definiteness

D. The induced normed group

41 declarations

definition

Order-unit bounds of xx

Given an element xx in an ordered space EE with an Archimedean order unit 11, the set of order-unit bounds is the set of all non-negative real numbers r∈Rr \in \mathbb{R} such that −r⋅1≤x≤r⋅1-r \cdot 1 \le x \le r \cdot 1.

definition

Order-unit norm of xx

Given an element xx in an ordered space EE with an Archimedean order unit 11, the order-unit norm of xx is defined as the infimum of the set of all non-negative real numbers r∈Rr \in \mathbb{R} such that −r⋅1≤x≤r⋅1-r \cdot 1 \le x \le r \cdot 1.

theorem

The set of order-unit bounds for any xx is non-empty

Let EE be an ordered space with an Archimedean order unit 11. For any element x∈Ex \in E, the set of order-unit bounds {r∈R∣r≥0 and −r⋅1≤x≤r⋅1}\{r \in \mathbb{R} \mid r \ge 0 \text{ and } -r \cdot 1 \le x \le r \cdot 1\} is non-empty.

theorem

The set of order-unit bounds is bounded below by 00

Let EE be an ordered space with an Archimedean order unit 11. For any element x∈Ex \in E, the set of order-unit bounds {r∈R∣−r⋅1≤x≤r⋅1}\{r \in \mathbb{R} \mid -r \cdot 1 \le x \le r \cdot 1\} is bounded below in R\mathbb{R}. Specifically, this set is bounded below by 00.

theorem

The order-unit norm ∥x∥\|x\| is non-negative (0≤∥x∥0 \le \|x\|)

Let EE be an ordered space with an Archimedean order unit. For any element x∈Ex \in E, the order-unit norm of xx, denoted as ∥x∥\|x\|, is non-negative, i.e., 0≤∥x∥0 \le \|x\|. The order-unit norm is defined as the infimum of the set of non-negative real numbers rr such that −r⋅1≤x≤r⋅1-r \cdot 1 \le x \le r \cdot 1.

theorem

The order-unit norm is less than or equal to any order-unit bound (∥x∥≤r\|x\| \le r)

Let EE be an ordered space with an Archimedean order unit 11. For any element x∈Ex \in E and any real number r∈Rr \in \mathbb{R}, if rr is an order-unit bound of xx (that is, rr satisfies −r⋅1≤x≤r⋅1-r \cdot 1 \le x \le r \cdot 1), then the order-unit norm of xx is less than or equal to rr (∥x∥≤r\|x\| \le r).

theorem

The order-unit norm of zero is 00

Let EE be an ordered space with an Archimedean order unit. The order-unit norm of the zero element 0∈E0 \in E is 00, i.e., orderUnitNorm(0)=0\text{orderUnitNorm}(0) = 0.

theorem

orderUnitBounds(−x)=orderUnitBounds(x)\text{orderUnitBounds}(-x) = \text{orderUnitBounds}(x)

For any element xx in an ordered space EE with an Archimedean order unit 11, the set of order-unit bounds of −x-x is equal to the set of order-unit bounds of xx. Here, the set of order-unit bounds of xx is the set of non-negative real numbers r∈Rr \in \mathbb{R} such that −r⋅1≤x≤r⋅1-r \cdot 1 \le x \le r \cdot 1.

theorem

orderUnitNorm(−x)=orderUnitNorm(x)\text{orderUnitNorm}(-x) = \text{orderUnitNorm}(x)

For any element xx in an ordered space EE with an Archimedean order unit, the order-unit norm of the negation of xx is equal to the order-unit norm of xx, that is, orderUnitNorm(−x)=orderUnitNorm(x)\text{orderUnitNorm}(-x) = \text{orderUnitNorm}(x).

theorem

The sum of order-unit bounds is an order-unit bound of the sum

Let EE be an ordered space with an Archimedean order unit 11. For any elements x,y∈Ex, y \in E and real numbers r,s∈Rr, s \in \mathbb{R}, if rr is an order-unit bound of xx (that is, −r⋅1≤x≤r⋅1-r \cdot 1 \le x \le r \cdot 1) and ss is an order-unit bound of yy (that is, −s⋅1≤y≤s⋅1-s \cdot 1 \le y \le s \cdot 1), then their sum r+sr + s is an order-unit bound of x+yx + y (that is, −(r+s)⋅1≤x+y≤(r+s)⋅1-(r + s) \cdot 1 \le x + y \le (r + s) \cdot 1).

theorem

Existence of an order-unit bound r<∥x∥+εr < \|x\| + \varepsilon

Let EE be an ordered space with an Archimedean order unit 11. For any element x∈Ex \in E and any real number ε>0\varepsilon > 0, there exists an order-unit bound rr of xx (that is, a real number rr satisfying −r⋅1≤x≤r⋅1-r \cdot 1 \le x \le r \cdot 1) such that rr is strictly less than the sum of the order-unit norm of xx and ε\varepsilon: r<∥x∥+εr < \|x\| + \varepsilon where ∥x∥\|x\| denotes the order-unit norm of xx, defined as the infimum of all such bounds rr.

theorem

Triangle Inequality for the Order-Unit Norm: ∥x+y∥≤∥x∥+∥y∥\|x + y\| \leq \|x\| + \|y\|

Let EE be an ordered space with an Archimedean order unit. For any elements x,y∈Ex, y \in E, the order-unit norm ∥⋅∥\|\cdot\| satisfies the triangle inequality: ∥x+y∥≤∥x∥+∥y∥\|x + y\| \leq \|x\| + \|y\| where the order-unit norm ∥x∥\|x\| is defined as the infimum of all r∈Rr \in \mathbb{R} such that −r⋅1≤x≤r⋅1-r \cdot 1 \le x \le r \cdot 1.

theorem

orderUnitNorm(x)=0  ⟹  x≤ε⋅1\text{orderUnitNorm}(x) = 0 \implies x \le \varepsilon \cdot 1 for all ε>0\varepsilon > 0

Let EE be an ordered space with an Archimedean order unit 11. If the order-unit norm of an element x∈Ex \in E is zero (i.e., orderUnitNorm(x)=0\text{orderUnitNorm}(x) = 0), then for any real number ε>0\varepsilon > 0, the element xx is bounded above by the ε\varepsilon-multiple of the unit, such that x≤ε⋅1x \le \varepsilon \cdot 1.

theorem

orderUnitNorm(x)=0  ⟺  x=0\text{orderUnitNorm}(x) = 0 \iff x = 0

In an ordered space EE with an Archimedean order unit 11, the order-unit norm of an element x∈Ex \in E, denoted by orderUnitNorm(x)\text{orderUnitNorm}(x), is equal to 00 if and only if x=0x = 0.

definition

Order-unit norm as an additive group norm

In an ordered space EE with an Archimedean order unit 11, the order-unit norm ∥⋅∥\|\cdot\| is the additive group norm defined by ∥x∥=inf⁡{r∈R≥0∣−r⋅1≤x≤r⋅1}\|x\| = \inf \{r \in \mathbb{R}_{\ge 0} \mid -r \cdot 1 \le x \le r \cdot 1\}. This structure packages the function x↦orderUnitNorm(x)x \mapsto \text{orderUnitNorm}(x) with the necessary proofs that it satisfies the norm axioms: ∥0∥=0\|0\| = 0, the triangle inequality ∥x+y∥≤∥x∥+∥y∥\|x + y\| \le \|x\| + \|y\|, the symmetry property ∥−x∥=∥x∥\|-x\| = \|x\|, and the positive definiteness property ∥x∥=0  ⟺  x=0\|x\| = 0 \iff x = 0.

definition

Normed additive commutative group structure induced by the order-unit norm

In an ordered additive commutative group EE equipped with an Archimedean order unit 11, this definition establishes the structure of a normed additive commutative group (`NormedAddCommGroup`) on EE. The norm used is the order-unit norm ∥x∥\|x\|, which is defined as the infimum of all r∈R≥0r \in \mathbb{R}_{\ge 0} such that −r⋅1≤x≤r⋅1-r \cdot 1 \le x \le r \cdot 1. This structure equips EE with a metric space topology where the distance between two elements xx and yy is given by ∥x−y∥\|x - y\|.

theorem

x≤∥x∥⋅1x \le \|x\| \cdot 1 for the order-unit norm

In an ordered space EE with an Archimedean order unit 11, for any element x∈Ex \in E, the inequality x≤∥x∥⋅1x \le \|x\| \cdot 1 holds, where ∥x∥\|x\| denotes the order-unit norm of xx. This norm ∥x∥\|x\| is defined as the infimum of the set of all non-negative real numbers rr such that −r⋅1≤x≤r⋅1-r \cdot 1 \le x \le r \cdot 1.

theorem

−∥x∥⋅1≤x-\|x\| \cdot 1 \le x for the order-unit norm

Let EE be an ordered space with an Archimedean order unit 11. For any element x∈Ex \in E, the inequality −∥x∥⋅1≤x-\|x\| \cdot 1 \le x holds, where ∥x∥\|x\| is the order-unit norm of xx, defined as the infimum of the set of all non-negative real numbers rr such that −r⋅1≤x≤r⋅1-r \cdot 1 \le x \le r \cdot 1.

theorem

The Order-Unit Norm ∥x∥\|x\| is an Order-Unit Bound of xx

In an ordered space EE with an Archimedean order unit 11, for any element x∈Ex \in E, the order-unit norm of xx, denoted as ∥x∥\|x\|, is itself an order-unit bound of xx. That is, the infimum defining the norm is attained, satisfying the inequality −∥x∥⋅1≤x≤∥x∥⋅1-\|x\| \cdot 1 \le x \le \|x\| \cdot 1.

theorem

r∈orderUnitBounds x  ⟺  orderUnitNorm x≤rr \in \text{orderUnitBounds } x \iff \text{orderUnitNorm } x \le r

Let EE be an ordered space with an Archimedean order unit 11. For any element x∈Ex \in E and any real number r∈Rr \in \mathbb{R}, rr is an order-unit bound of xx (that is, −r⋅1≤x≤r⋅1-r \cdot 1 \le x \le r \cdot 1) if and only if rr is greater than or equal to the order-unit norm of xx, denoted as orderUnitNorm x\text{orderUnitNorm } x.

definition

Real normed space structure induced by the order-unit norm

Given an ordered additive commutative group EE with an Archimedean order unit 11, this definition establishes a normed space structure over the real numbers R\mathbb{R} on EE. The norm is the order-unit norm ∥x∥\|x\|, defined for any x∈Ex \in E as the infimum of the set of all r∈R≥0r \in \mathbb{R}_{\ge 0} such that −r⋅1≤x≤r⋅1-r \cdot 1 \le x \le r \cdot 1. This structure is built upon the normed additive commutative group structure previously induced by the same order-unit norm.

theorem

The positive cone {x∈E∣0≤x}\{x \in E \mid 0 \le x\} is closed in the order-unit norm topology

Let EE be an ordered additive commutative group with an Archimedean order unit. The set of non-negative elements {x∈E∣0≤x}\{x \in E \mid 0 \le x\} (the positive cone) is closed in the topology induced by the order-unit norm ∥x∥=inf⁡{r∈R≥0∣−r⋅1≤x≤r⋅1}\|x\| = \inf \{r \in \mathbb{R}_{\ge 0} \mid -r \cdot 1 \le x \le r \cdot 1\}.

theorem

The order-unit norm on R\mathbb{R} is the absolute value ∣x∣|x|

For any real number x∈Rx \in \mathbb{R}, the order-unit norm of xx (defined with respect to the classical order unit 11) is equal to its absolute value ∣x∣|x|.

definition

The type EE equipped with the order-unit norm

Let EE be a type (typically an ordered vector space with an Archimedean order unit). `WithOrderUnitNorm E` is a type synonym for EE that is canonically equipped with the order-unit norm. For an element x∈Ex \in E, this norm is defined as ∥x∥=inf⁡{r∈R∣−r⋅1≤x≤r⋅1}\|x\| = \inf \{ r \in \mathbb{R} \mid -r \cdot \mathbf{1} \le x \le r \cdot \mathbf{1} \}, where 1\mathbf{1} is the order unit. This construction allows EE to carry the order-unit norm structure even if the original type EE is already equipped with a different norm for other purposes.

instance

Additive commutative group structure on `WithOrderUnitNorm E`

The type synonym `WithOrderUnitNorm E`, representing the type EE equipped with the order-unit norm, inherits the additive commutative group structure from the underlying type EE. This means the operations of addition, negation, and the zero element on `WithOrderUnitNorm E` are identical to those defined on EE.

instance

R\mathbb{R}-module structure on `WithOrderUnitNorm E`

The type synonym `WithOrderUnitNorm E`, representing the type EE equipped with the order-unit norm, inherits the module structure over the real numbers R\mathbb{R} from the underlying type EE. This defines the scalar multiplication of elements in `WithOrderUnitNorm E` by real numbers.

instance

Partial order on `WithOrderUnitNorm E`

The type synonym `WithOrderUnitNorm E` inherits the partial order structure ≤\le from the underlying type EE.

instance

`WithOrderUnitNorm E` is an ordered additive monoid

The type synonym `WithOrderUnitNorm E`, which represents the space EE equipped with the order-unit norm, inherits the structure of an ordered additive monoid from EE. This means that the addition operation and the partial order ≤\le are compatible: for any elements a,b,c∈WithOrderUnitNorm Ea, b, c \in \text{WithOrderUnitNorm } E, if a≤ba \le b, then a+c≤b+ca + c \le b + c.

instance

Scalar multiplication by non-negative real numbers is monotone in `WithOrderUnitNorm E`

In the space EE equipped with the order-unit norm, scalar multiplication by non-negative real numbers is monotone. Specifically, for any real number r≥0r \ge 0 and any elements x,y∈Ex, y \in E, if x≤yx \le y, then r⋅x≤r⋅yr \cdot x \le r \cdot y.

instance

Unit element 11 of `WithOrderUnitNorm E`

The type `WithOrderUnitNorm E` is equipped with a unit element 11, which represents the order unit 1\mathbf{1} used in the definition of the order-unit norm and for comparing elements within the ordered space.

instance

The unit 11 is an order unit in `WithOrderUnitNorm E`

In the space EE equipped with the order-unit norm, the unit element 11 is an order unit. This means that for every element x∈Ex \in E, there exists a real number rr such that −r⋅1≤x≤r⋅1-r \cdot 1 \le x \le r \cdot 1, where ≤\le is the partial order inherited from EE.

instance

The unit 11 is an Archimedean order unit in `WithOrderUnitNorm E`

In the type synonym `WithOrderUnitNorm E`, which represents the space EE equipped with the order-unit norm, the unit element 11 is an Archimedean order unit. This implies that 11 is an order unit for the space and that the order structure satisfies the Archimedean property, allowing the order-unit norm to be well-defined as a genuine norm.

instance

Normed additive commutative group structure for `WithOrderUnitNorm E`

Let EE be an ordered additive commutative group with an Archimedean order unit 1\mathbf{1}. The type `WithOrderUnitNorm E` (a type synonym for EE) is equipped with the structure of a normed additive commutative group. The norm ∥⋅∥\| \cdot \| on this group is the order-unit norm, defined as ∥x∥=inf⁡{r∈R∣−r⋅1≤x≤r⋅1}\|x\| = \inf \{ r \in \mathbb{R} \mid -r \cdot \mathbf{1} \le x \le r \cdot \mathbf{1} \}.

instance

Real normed space structure on `WithOrderUnitNorm E`

Let EE be an ordered vector space with an Archimedean order unit 1\mathbf{1}. The type synonym `WithOrderUnitNorm E` is canonically equipped with the structure of a normed space over the real numbers R\mathbb{R}. The norm ∥⋅∥\|\cdot\| associated with this structure is the order-unit norm, defined for any element x∈Ex \in E as ∥x∥=inf⁡{r∈R∣−r⋅1≤x≤r⋅1} \|x\| = \inf \{ r \in \mathbb{R} \mid -r \cdot \mathbf{1} \le x \le r \cdot \mathbf{1} \} This definition ensures that the scalar multiplication and addition in EE are compatible with the topology induced by this norm.

definition

Linear equivalence E≃EE \simeq E with the order-unit norm

Let EE be a real vector space (typically an ordered vector space with an Archimedean order unit). This is the R\mathbb{R}-linear equivalence between EE and its type synonym `WithOrderUnitNorm E`, which is the space EE equipped with the order-unit norm ∥x∥=inf⁡{r∈R∣−r⋅1≤x≤r⋅1}\|x\| = \inf \{ r \in \mathbb{R} \mid -r \cdot \mathbf{1} \le x \le r \cdot \mathbf{1} \}. The map is the identity on the underlying elements.

theorem

The linear equivalence between EE and its order-unit norm synonym is the identity map

Let EE be a real vector space and let WithOrderUnitNorm E\text{WithOrderUnitNorm } E be the type synonym for EE equipped with the order-unit norm. The canonical R\mathbb{R}-linear equivalence ϕ:E≃RWithOrderUnitNorm E\phi : E \simeq_{\mathbb{R}} \text{WithOrderUnitNorm } E acts as the identity map on the underlying elements, such that for any x∈Ex \in E, ϕ(x)=x\phi(x) = x.

theorem

The norm on WithOrderUnitNorm E\text{WithOrderUnitNorm } E equals the order-unit norm

Let EE be an ordered vector space with an Archimedean order unit 1\mathbf{1}. For any element xx in the type synonym WithOrderUnitNorm E\text{WithOrderUnitNorm } E (representing EE equipped with the order-unit norm), the norm ∥x∥\|x\| is equal to the order-unit norm of the corresponding element in EE, which is defined as inf⁡{r∈R∣−r⋅1≤x≤r⋅1}\inf \{ r \in \mathbb{R} \mid -r \cdot \mathbf{1} \le x \le r \cdot \mathbf{1} \}.

definition

Linear isometry WithOrderUnitNorm R≃R\text{WithOrderUnitNorm } \mathbb{R} \simeq \mathbb{R}

The linear isometry equivalence between the real numbers R\mathbb{R} equipped with the order-unit norm and the standard real numbers R\mathbb{R} with the absolute value norm. For an element x∈Rx \in \mathbb{R}, the order-unit norm induced by the unit 11 is defined as ∥x∥=inf⁡{r∈R∣−r≤x≤r}\|x\| = \inf \{ r \in \mathbb{R} \mid -r \le x \le r \}, which is equal to the standard absolute value ∣x∣|x|. This equivalence acts as the canonical identification between the order-unit space structure of R\mathbb{R} and its standard topological and normed structure.

theorem

realLinearIsometryEquiv(x)=x\text{realLinearIsometryEquiv}(x) = x

Let xx be a real number viewed as an element of the type synonym WithOrderUnitNorm R\text{WithOrderUnitNorm } \mathbb{R}. The application of the linear isometry equivalence `realLinearIsometryEquiv` to xx results in the real number xx.

instance

R\mathbb{R} with the order-unit norm is a complete space

The set of real numbers R\mathbb{R}, equipped with the order-unit norm ∥⋅∥\|\cdot\| induced by the order unit 11 (where ∥x∥=∣x∣\|x\| = |x|), is a complete space.

theorem

Unital Positive Linear Maps are Contractive for Order-Unit Norm

Let EE and FF be ordered vector spaces equipped with Archimedean order units. For any unital positive linear map ϕ:E→F\phi : E \to F and any element x∈Ex \in E, the order-unit norm of the image ϕ(x)\phi(x) is bounded by the order-unit norm of xx: ∥ϕ(x)∥≤∥x∥ \|\phi(x)\| \leq \|x\| where the order-unit norm ∥⋅∥\|\cdot\| is defined as ∥y∥=inf⁡{r∈R≥0∣−r⋅1≤y≤r⋅1}\|y\| = \inf \{r \in \mathbb{R}_{\ge 0} \mid -r \cdot 1 \le y \le r \cdot 1\}.