PhyslibAlpha.Mathematics.Order.PositiveDual.Bidual
The bidual
i. Overview
An element of an ordered real vector space `E` assigns to every positive functional its value, additively and positively homogeneously, and dominated by the values of some element of `E`. The bidual consists of all such assignments. It contains `E` when the order is directed, and is ordered by comparing values on every positive functional. Positive functionals extend to the bidual by evaluation.
The bidual is monotone complete: a bounded upward directed family of elements has a least upper bound, their pointwise supremum.
ii. Key results
- `Bidual E` : the bidual of `E`. - `Bidual.ofE` : an element of `E` as an element of the bidual. - `Bidual.eval` : a positive functional extended to the bidual. - `Bidual.isLUB_ciSup` : a bounded directed family in the bidual has its pointwise supremum as least upper bound.
iii. Table of contents
- A. The bidual
- B. Order
- C. Elements and positive functionals
- D. Monotone completeness
A. The bidual
B. Order
C. Elements and positive functionals
D. Monotone completeness
36 declarations
Submodule of the bidual of
The `bidualSubmodule` is the -submodule of the space of real-valued functions on the set of positive functionals of an ordered real vector space (denoted ). A function belongs to this submodule if it satisfies the following three conditions: 1. **Additivity**: for all positive functionals . 2. **Positive homogeneity**: for all and positive functionals . 3. **Domination**: There exists an element such that for all positive functionals .
Bidual of an ordered real vector space
Let be an ordered real vector space and let denote the set of positive linear functionals on . The bidual of , denoted as , is defined as the -submodule of functions that satisfy the following conditions: 1. **Additivity**: for all . 2. **Positive homogeneity**: for all and . 3. **Domination**: There exists an element such that for all .
is an additive commutative group
The bidual of an ordered real vector space carries the structure of an additive commutative group, where addition and negation are defined pointwise on the functions from positive linear functionals to that constitute the space.
is a vector space over
The bidual of an ordered real vector space carries the structure of a vector space (module) over the real numbers . The addition and scalar multiplication are defined pointwise, inheriting the module structure from the space of functions .
Construct an element of from an additive, positively homogeneous, and dominated function
Let be an ordered real vector space and let denote the set of positive linear functionals on . Given a function that satisfies: 1. **Additivity**: for all , 2. **Positive homogeneity**: for all and , 3. **Domination**: There exists an element such that for all , this definition constructs the corresponding element in the bidual .
Bidual element as an element of the submodule
Given an element of the bidual of an ordered real vector space , this function maps to its representation as an element of the -submodule of functions that are additive, positively homogeneous, and dominated by some element of .
Coercion of to functions
Let be an ordered real vector space. This instance allows an element of the bidual to be treated as a function mapping from the set of positive linear functionals to the real numbers . Thus, for a positive linear functional , the value is defined.
Evaluation of the constructed bidual element
Let be an ordered real vector space and let denote the set of positive linear functionals on . Suppose is a function that is additive, positively homogeneous, and dominated by an element of . Then the element of the bidual constructed from (denoted as ), when evaluated at a positive functional , is equal to .
Extensionality of elements in the bidual ()
Let be an ordered real vector space and be its bidual. For any elements , if for every positive linear functional , then .
for
Let be an ordered real vector space and be its bidual. For any element and any two positive linear functionals , the function preserves addition, such that .
for elements of the bidual
Let be an ordered real vector space and be its bidual. For any element , any non-negative real number , and any positive linear functional on , the evaluation of at the scaled functional satisfies .
Every element of the bidual is dominated by an element of
Let be an ordered real vector space and denote its bidual. For every element , there exists an element such that for all positive linear functionals on , we have .
A dominating element has non-negative values on positive functionals.
Let be an ordered real vector space and its bidual. For any element and any , if the condition holds for all positive functionals , then it follows that for every such .
Addition in the Bidual is Pointwise:
Let be an ordered real vector space. For any two elements in the bidual and any positive linear functional , the addition in the bidual is defined pointwise such that .
in the Bidual
Let be an ordered real vector space and its bidual. For any elements and any positive linear functional , the evaluation of the difference at satisfies .
for elements of the Bidual
Let be an ordered real vector space and its bidual. For any element and any positive linear functional , the evaluation of the negated element at is equal to the negation of the value of at :
Let be an ordered real vector space and be its bidual. For any positive linear functional , the evaluation of the zero element at is equal to .
for elements of the Bidual
Let be an ordered real vector space and its bidual. For any scalar , any element , and any positive linear functional , the evaluation of the scalar product at is equal to the product of and the value of at :
for
Let be an ordered real vector space and let denote the set of positive linear functionals on . For any element of the bidual , the evaluation of at the zero functional is zero, i.e., .
Bidual elements are additive over finite sums of positive functionals
Let be an ordered real vector space and be its bidual. For any element , any finite set of indices , and any collection of positive functionals where each , the value of applied to the sum of the functionals is equal to the sum of the values of applied to each functional:
Partial order on
The bidual of an ordered real vector space is equipped with a partial order defined pointwise. For any two elements , the relation holds if and only if for every positive linear functional on .
in
Let be an ordered real vector space and be its bidual. For any two elements , the relation holds if and only if for every positive linear functional on .
is an Ordered Additive Monoid
Let be an ordered real vector space. The bidual space , equipped with its pointwise addition and pointwise partial order, forms an ordered additive monoid. Specifically, for any elements , if , then .
and in
Let be an ordered real vector space. In the bidual , scalar multiplication by non-negative real numbers preserves the order relation. Specifically, for any real number and any elements , if , then .
Canonical linear map
Let be an ordered real vector space. The canonical -linear map sends an element to the element of the bidual defined by evaluation. Specifically, for any positive linear functional , the resulting element of the bidual maps to the value .
Let be an ordered real vector space. For any element and any positive linear functional on , the canonical map satisfies the identity .
Let be an ordered real vector space. For any elements , if , then , where is the canonical linear map from to its bidual.
The bidual is a directed order
Let be an ordered real vector space. If is a directed order, then the bidual is also a directed order. This means that for any two elements , there exists an element such that and . Specifically, if is dominated by and is dominated by , then the element serves as an upper bound for both and .
Evaluation of a positive functional on
For a positive linear functional on an ordered real vector space (denoted ), this function defines a positive linear functional on the bidual by evaluation. Specifically, for an element , the functional maps to its value .
Let be an ordered real vector space. For any positive linear functional and any element , the evaluation of on is defined by applying the function to :
Let be an ordered real vector space. For any positive linear functional and any element , the evaluation of the extended functional at the canonical image in the bidual is equal to the value of the functional at :
Let be an ordered real vector space. For any two positive linear functionals on (denoted ), if , then their extensions to the bidual by evaluation satisfy . This theorem states that the extension to the bidual preserves the order of positive functionals.
Boundedness in the Bidual implies Pointwise Boundedness on Positive Functionals
Let be an ordered real vector space and its bidual. If a family of elements in is bounded above, then for any positive linear functional on (denoted ), the set of real values is bounded above in .
Pointwise supremum in
Let be an ordered real vector space and let be its bidual. For a directed family of elements in that is bounded above, the function is the element of defined by the pointwise supremum of the family. Specifically, for any positive linear functional on , the value of the supremum is given by .
in
Let be an ordered real vector space and let be a directed family of elements in the bidual that is bounded above. For any positive linear functional on (denoted ), the value of the supremum of the family evaluated at is equal to the supremum of the individual values in :
The Pointwise Supremum is the Least Upper Bound in the Bidual
Let be an ordered real vector space and be its bidual. Let be a directed family of elements in that is bounded above. Then the pointwise supremum of this family, denoted by and defined such that for every positive linear functional on , is the least upper bound of the range in the partial order of .
