PhyslibAlpha.Mathematics.Order.PositiveDual.Basic
Positive functionals
i. Overview
A positive functional on an ordered real vector space `E` is a linear functional that is nonnegative on the positive cone. When the order is directed, every element is a difference of two nonnegative ones, so positive functionals are determined by their values on the cone. They are then ordered by comparing these values: `ψ ≤ φ` when `φ - ψ` is positive again.
Conversely, a nonnegative function on the cone that is additive and positively homogeneous there extends uniquely to a positive functional.
ii. Key results
- `PositiveLinearMap.instPartialOrder` : positive functionals ordered on the positive cone. - `PositiveLinearMap.subOfLE` : the difference of two positive functionals, one below the other. - `PositiveLinearMap.eq_zero_of_map_eq_zero` : a positive functional vanishing at an order unit vanishes. - `PositiveLinearMap.ofCone` : a nonnegative, additive, positively homogeneous function on the cone as a positive functional.
iii. Table of contents
- A. Scaling positive functionals
- B. The order on positive functionals
- C. Extending from the cone
A. Scaling positive functionals
B. The order on positive functionals
C. Extending from the cone
23 declarations
Scalar multiplication of positive functionals by
Let be an ordered real vector space and let denote the space of positive linear functionals on . This definition provides the scalar multiplication of a positive linear functional by a non-negative real number , such that for any , the result is given by .
for positive linear functionals and non-negative scalars
Let be an ordered real vector space. For any non-negative real number , any positive linear functional (a linear functional that is non-negative on the positive cone of ), and any element , the scalar multiplication of the functional is defined pointwise such that .
An element and
For an element in an ordered real vector space , this function selects an element in that is greater than or equal to both and the zero element . Specifically, it satisfies and .
for elements in an ordered real vector space
Let be an ordered real vector space. For any element , it holds that , where is defined as an element in that is greater than or equal to both and the zero element .
The dominator of is non-negative ()
Let be an ordered real vector space. For any element , its dominator is non-negative, satisfying . Here, the dominator of is an element in defined to be greater than or equal to both and the zero element .
Partial order on positive linear maps
For an ordered real vector space , the space of positive linear functionals is equipped with a partial order. A positive functional is defined to be less than or equal to () if and only if for every element in the positive cone of (i.e., for all ).
Let be an ordered real vector space. For any two positive linear functionals , the inequality holds if and only if for every element in the positive cone (i.e., ), the values satisfy .
for any positive linear functional
Let be an ordered real vector space. For any positive linear functional from to , it holds that under the partial order of positive linear maps.
for positive linear functionals
Let be an ordered real vector space. For any two positive linear functionals from to , it holds that under the partial order of positive linear functionals.
for positive linear functionals
Let be an ordered real vector space. Let be a collection of positive linear functionals from to (denoted as ), where is an indexing set. For any finite subset and any index , the functional is less than or equal to the sum of the functionals in under the partial order on positive linear functionals: This means that for all elements in the positive cone of (), the inequality holds.
Difference of positive linear functionals given
Given an ordered real vector space and two positive linear functionals such that (meaning for all in the positive cone of ), this definition constructs the positive linear functional representing their difference . The resulting functional is defined by for all , and its positivity is guaranteed by the condition .
Evaluation of the difference of positive linear functionals:
Let be an ordered real vector space. Suppose and are positive linear functionals from to such that (meaning for all in the positive cone of ). For any element , the positive linear functional representing their difference (denoted as `subOfLE φ ψ h`) satisfies:
for positive linear functionals
Let be an ordered real vector space. For any two positive linear functionals , if (meaning for all in the positive cone of ), then the sum of and the positive linear functional representing the difference is equal to .
Extension of from the positive cone to
For an ordered real vector space and a function defined on its positive cone , the function `coneExt` extends to the entire space . For any element , it is defined as , where is a chosen "dominator" satisfying and .
for additive functions on the positive cone
Let be an ordered real vector space and let be an additive function defined on its positive cone (the set of elements such that ). Then the value of at the zero element is zero, i.e., .
for any
Let be an ordered real vector space and let be a function defined on its positive cone . For any element and any element satisfying and , the extension of to the whole space , denoted by , is given by: This formula characterizes the extension of using a "dominator" element that is greater than or equal to both and , ensuring that both and lie within the positive cone where is defined.
for
Let be an ordered real vector space and be a function defined on its positive cone . For any element such that , the value of the extension at is equal to the value of the original function at , i.e., .
Additivity of the cone extension
Let be an ordered real vector space and let be a function defined on its positive cone. The extension of to the entire space , denoted by , is additive. That is, for any vectors , it holds that .
Let be an ordered real vector space and be a function defined on its positive cone . Let denote the extension of to the entire space . For any element , the extension satisfies
Positive Homogeneity of the Cone Extension for
Let be an ordered real vector space and let be a function defined on its positive cone. Let be the extension of to the entire space . For any positive real scalar and any vector , the extension satisfies the property .
The cone extension is homogeneous under scalar multiplication:
Let be an ordered real vector space and be a function defined on its positive cone . Let denote the extension of to the entire space . For any scalar and any element , the extension satisfies .
Positive linear functional extension from the positive cone
Let be an ordered real vector space. Given a function defined on the positive cone , the definition `ofCone` constructs a positive linear functional by extending to the entire space. This construction requires to be nonnegative (), additive (), and positively homogeneous ( for ) on the cone.
The extended positive linear functional agrees with on the positive cone
Let be an ordered real vector space and be a function defined on the positive cone that is nonnegative, additive, and positively homogeneous. Let be the positive linear functional on constructed by extending . For any element in the positive cone (i.e., ), the value of the extended functional at matches the original function: .
