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
Order-unit bounds of
Given an element in an ordered space with an Archimedean order unit , the set of order-unit bounds is the set of all non-negative real numbers such that .
Order-unit norm of
Given an element in an ordered space with an Archimedean order unit , the order-unit norm of is defined as the infimum of the set of all non-negative real numbers such that .
The set of order-unit bounds for any is non-empty
Let be an ordered space with an Archimedean order unit . For any element , the set of order-unit bounds is non-empty.
The set of order-unit bounds is bounded below by
Let be an ordered space with an Archimedean order unit . For any element , the set of order-unit bounds is bounded below in . Specifically, this set is bounded below by .
The order-unit norm is non-negative ()
Let be an ordered space with an Archimedean order unit. For any element , the order-unit norm of , denoted as , is non-negative, i.e., . The order-unit norm is defined as the infimum of the set of non-negative real numbers such that .
The order-unit norm is less than or equal to any order-unit bound ()
Let be an ordered space with an Archimedean order unit . For any element and any real number , if is an order-unit bound of (that is, satisfies ), then the order-unit norm of is less than or equal to ().
The order-unit norm of zero is
Let be an ordered space with an Archimedean order unit. The order-unit norm of the zero element is , i.e., .
For any element in an ordered space with an Archimedean order unit , the set of order-unit bounds of is equal to the set of order-unit bounds of . Here, the set of order-unit bounds of is the set of non-negative real numbers such that .
For any element in an ordered space with an Archimedean order unit, the order-unit norm of the negation of is equal to the order-unit norm of , that is, .
The sum of order-unit bounds is an order-unit bound of the sum
Let be an ordered space with an Archimedean order unit . For any elements and real numbers , if is an order-unit bound of (that is, ) and is an order-unit bound of (that is, ), then their sum is an order-unit bound of (that is, ).
Existence of an order-unit bound
Let be an ordered space with an Archimedean order unit . For any element and any real number , there exists an order-unit bound of (that is, a real number satisfying ) such that is strictly less than the sum of the order-unit norm of and : where denotes the order-unit norm of , defined as the infimum of all such bounds .
Triangle Inequality for the Order-Unit Norm:
Let be an ordered space with an Archimedean order unit. For any elements , the order-unit norm satisfies the triangle inequality: where the order-unit norm is defined as the infimum of all such that .
for all
Let be an ordered space with an Archimedean order unit . If the order-unit norm of an element is zero (i.e., ), then for any real number , the element is bounded above by the -multiple of the unit, such that .
In an ordered space with an Archimedean order unit , the order-unit norm of an element , denoted by , is equal to if and only if .
Order-unit norm as an additive group norm
In an ordered space with an Archimedean order unit , the order-unit norm is the additive group norm defined by . This structure packages the function with the necessary proofs that it satisfies the norm axioms: , the triangle inequality , the symmetry property , and the positive definiteness property .
Normed additive commutative group structure induced by the order-unit norm
In an ordered additive commutative group equipped with an Archimedean order unit , this definition establishes the structure of a normed additive commutative group (`NormedAddCommGroup`) on . The norm used is the order-unit norm , which is defined as the infimum of all such that . This structure equips with a metric space topology where the distance between two elements and is given by .
for the order-unit norm
In an ordered space with an Archimedean order unit , for any element , the inequality holds, where denotes the order-unit norm of . This norm is defined as the infimum of the set of all non-negative real numbers such that .
for the order-unit norm
Let be an ordered space with an Archimedean order unit . For any element , the inequality holds, where is the order-unit norm of , defined as the infimum of the set of all non-negative real numbers such that .
The Order-Unit Norm is an Order-Unit Bound of
In an ordered space with an Archimedean order unit , for any element , the order-unit norm of , denoted as , is itself an order-unit bound of . That is, the infimum defining the norm is attained, satisfying the inequality .
Let be an ordered space with an Archimedean order unit . For any element and any real number , is an order-unit bound of (that is, ) if and only if is greater than or equal to the order-unit norm of , denoted as .
Real normed space structure induced by the order-unit norm
Given an ordered additive commutative group with an Archimedean order unit , this definition establishes a normed space structure over the real numbers on . The norm is the order-unit norm , defined for any as the infimum of the set of all such that . This structure is built upon the normed additive commutative group structure previously induced by the same order-unit norm.
The positive cone is closed in the order-unit norm topology
Let be an ordered additive commutative group with an Archimedean order unit. The set of non-negative elements (the positive cone) is closed in the topology induced by the order-unit norm .
The order-unit norm on is the absolute value
For any real number , the order-unit norm of (defined with respect to the classical order unit ) is equal to its absolute value .
The type equipped with the order-unit norm
Let be a type (typically an ordered vector space with an Archimedean order unit). `WithOrderUnitNorm E` is a type synonym for that is canonically equipped with the order-unit norm. For an element , this norm is defined as , where is the order unit. This construction allows to carry the order-unit norm structure even if the original type is already equipped with a different norm for other purposes.
Additive commutative group structure on `WithOrderUnitNorm E`
The type synonym `WithOrderUnitNorm E`, representing the type equipped with the order-unit norm, inherits the additive commutative group structure from the underlying type . This means the operations of addition, negation, and the zero element on `WithOrderUnitNorm E` are identical to those defined on .
-module structure on `WithOrderUnitNorm E`
The type synonym `WithOrderUnitNorm E`, representing the type equipped with the order-unit norm, inherits the module structure over the real numbers from the underlying type . This defines the scalar multiplication of elements in `WithOrderUnitNorm E` by real numbers.
Partial order on `WithOrderUnitNorm E`
The type synonym `WithOrderUnitNorm E` inherits the partial order structure from the underlying type .
`WithOrderUnitNorm E` is an ordered additive monoid
The type synonym `WithOrderUnitNorm E`, which represents the space equipped with the order-unit norm, inherits the structure of an ordered additive monoid from . This means that the addition operation and the partial order are compatible: for any elements , if , then .
Scalar multiplication by non-negative real numbers is monotone in `WithOrderUnitNorm E`
In the space equipped with the order-unit norm, scalar multiplication by non-negative real numbers is monotone. Specifically, for any real number and any elements , if , then .
Unit element of `WithOrderUnitNorm E`
The type `WithOrderUnitNorm E` is equipped with a unit element , which represents the order unit used in the definition of the order-unit norm and for comparing elements within the ordered space.
The unit is an order unit in `WithOrderUnitNorm E`
In the space equipped with the order-unit norm, the unit element is an order unit. This means that for every element , there exists a real number such that , where is the partial order inherited from .
The unit is an Archimedean order unit in `WithOrderUnitNorm E`
In the type synonym `WithOrderUnitNorm E`, which represents the space equipped with the order-unit norm, the unit element is an Archimedean order unit. This implies that 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.
Normed additive commutative group structure for `WithOrderUnitNorm E`
Let be an ordered additive commutative group with an Archimedean order unit . The type `WithOrderUnitNorm E` (a type synonym for ) is equipped with the structure of a normed additive commutative group. The norm on this group is the order-unit norm, defined as .
Real normed space structure on `WithOrderUnitNorm E`
Let be an ordered vector space with an Archimedean order unit . The type synonym `WithOrderUnitNorm E` is canonically equipped with the structure of a normed space over the real numbers . The norm associated with this structure is the order-unit norm, defined for any element as This definition ensures that the scalar multiplication and addition in are compatible with the topology induced by this norm.
Linear equivalence with the order-unit norm
Let be a real vector space (typically an ordered vector space with an Archimedean order unit). This is the -linear equivalence between and its type synonym `WithOrderUnitNorm E`, which is the space equipped with the order-unit norm . The map is the identity on the underlying elements.
The linear equivalence between and its order-unit norm synonym is the identity map
Let be a real vector space and let be the type synonym for equipped with the order-unit norm. The canonical -linear equivalence acts as the identity map on the underlying elements, such that for any , .
The norm on equals the order-unit norm
Let be an ordered vector space with an Archimedean order unit . For any element in the type synonym (representing equipped with the order-unit norm), the norm is equal to the order-unit norm of the corresponding element in , which is defined as .
Linear isometry
The linear isometry equivalence between the real numbers equipped with the order-unit norm and the standard real numbers with the absolute value norm. For an element , the order-unit norm induced by the unit is defined as , which is equal to the standard absolute value . This equivalence acts as the canonical identification between the order-unit space structure of and its standard topological and normed structure.
Let be a real number viewed as an element of the type synonym . The application of the linear isometry equivalence `realLinearIsometryEquiv` to results in the real number .
with the order-unit norm is a complete space
The set of real numbers , equipped with the order-unit norm induced by the order unit (where ), is a complete space.
Unital Positive Linear Maps are Contractive for Order-Unit Norm
Let and be ordered vector spaces equipped with Archimedean order units. For any unital positive linear map and any element , the order-unit norm of the image is bounded by the order-unit norm of : where the order-unit norm is defined as .
