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PhyslibAlpha.ProbabilisticTheory.Weight.Continuous

Finite weights are continuous

i. Overview

A positive functional is bounded for the order-unit norm, `|ψ a| ≤ ψ 1 ‖a‖`. So every finite weight is a continuous linear functional on the observables with the order-unit norm.

ii. Key results

  • `PositiveLinearMap.abs_apply_le_apply_one_mul_orderUnitNorm` : `|ψ a| ≤ ψ 1 ‖a‖`.
  • `Weight.IsFinite.toOrderUnitContinuousLinearMap` : a finite weight as a continuous functional.

2 declarations

definition

Finite weight ww as a continuous linear map on (E,∥⋅∥1)(E, \|\cdot\|_{\mathbf{1}})

Let EE be an Archimedean order-unit space and let ∥⋅∥1\|\cdot\|_{\mathbf{1}} be its canonical order-unit norm. Given a finite weight w:E+→[0,∞)w : E^+ \to [0, \infty) defined on the positive cone of EE, this definition constructs its canonical extension to a continuous linear functional w~:(E,∥⋅∥1)→R\tilde{w} : (E, \|\cdot\|_{\mathbf{1}}) \to \mathbb{R}. The continuity is guaranteed by the property that ∣w~(x)∣≤w(1)∥x∥1|\tilde{w}(x)| \le w(\mathbf{1}) \|x\|_{\mathbf{1}} for all x∈Ex \in E.

theorem

The continuous linear map of a finite weight matches the weight on the positive cone

Let EE be an Archimedean order-unit space and let ww be a finite weight on its positive cone PosCone(E)\text{PosCone}(E). Let w~:(E,∥⋅∥1)→R\tilde{w}: (E, \|\cdot\|_{\mathbf{1}}) \to \mathbb{R} be the continuous linear map associated with ww. For any element xx in the positive cone PosCone(E)\text{PosCone}(E), the value of w~(x)\tilde{w}(x) is equal to the real-valued evaluation of the weight w(x)w(x).