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PhyslibAlpha.AlgebraicFramework.JordanOrderUnit.Conditioning

Conditioning a state by a Jordan projection

For a projection `p`, quadratic compression is `U_p`. Whenever `U_p` is positive and the state assigns nonzero probability to `p`, the normalized functional

`x ↦ ω(U_p x) / ω(p)`

is again a state. Positivity of `U_p` is an explicit hypothesis here: it is a theorem of JB spectral theory, not part of the weak `IsJordanOrderUnit` interface. This separation lets the conditioning construction live at its true level without postulating the missing JB theorem.

Quadratic conditioning

9 declarations

definition

Conditioning a state ω\omega on a Jordan projection pp

Given a Jordan projection pp in a Jordan order unit space EE and a state ω∈S(R,E)\omega \in \mathcal{S}(\mathbb{R}, E), if ω(p)>0\omega(p) > 0 and the quadratic representation UpU_p is a positive map, then the conditioned state is the unital positive linear map defined by x↦ω(Upx)ω(p)x \mapsto \frac{\omega(U_p x)}{\omega(p)} where UpU_p denotes the quadratic representation of the projection pp.

theorem

Evaluation of the Conditioned State ω∣p(x)\omega|_p(x)

Let EE be a Jordan order unit space, p∈Ep \in E be a Jordan projection, and ω\omega be a state on EE such that ω(p)>0\omega(p) > 0. Suppose the quadratic representation UpU_p is a positive map (i.e., it maps the positive cone of EE to itself). For any element x∈Ex \in E, the state ω\omega conditioned on the projection pp is evaluated as: condition(ω,p)(x)=ω(Upx)ω(p) \text{condition}(\omega, p)(x) = \frac{\omega(U_p x)}{\omega(p)} where UpU_p denotes the quadratic representation of the projection pp.

theorem

The conditioned state satisfies ω∣p(1)=1\omega_{|p}(1) = 1

Let EE be a Jordan order unit space and p∈Ep \in E be a Jordan projection. Let ω\omega be a state on EE such that ω(p)>0\omega(p) > 0, and let UpU_p be the quadratic representation of pp. Suppose UpU_p is a positive map. Then the conditioned state ω∣p\omega_{|p} (defined by x↦ω(Upx)ω(p)x \mapsto \frac{\omega(U_p x)}{\omega(p)}) is normalized, i.e., ω∣p(1)=1\omega_{|p}(1) = 1.

theorem

The conditioned state ω∣p\omega|_p is a positive map

Let EE be a Jordan order unit space, p∈Ep \in E be a Jordan projection, and ω\omega be a state on EE. Suppose that ω(p)>0\omega(p) > 0 and the quadratic representation UpU_p is a positive map (i.e., x≥0  ⟹  Upx≥0x \geq 0 \implies U_p x \geq 0). Then the conditioned state ω∣p\omega|_p, defined by the mapping x↦ω(Upx)ω(p)x \mapsto \frac{\omega(U_p x)}{\omega(p)}, is a positive functional. That is, for any x∈Ex \in E, if x≥0x \geq 0, then ω∣p(x)≥0\omega|_p(x) \geq 0.

theorem

Conditioning a state on a Jordan projection pp satisfies ω∣p(p)=1\omega|_p(p) = 1

Let EE be a Jordan order unit space and p∈Ep \in E be a Jordan projection. Let ω∈S(R,E)\omega \in \mathcal{S}(\mathbb{R}, E) be a state such that ω(p)>0\omega(p) > 0 and the quadratic representation UpU_p is a positive map. Then the state ω\omega conditioned on pp, defined by the mapping x↦ω(Upx)ω(p)x \mapsto \frac{\omega(U_p x)}{\omega(p)}, assigns the value 11 to the projection pp. That is, ω∣p(p)=1\omega|_p(p) = 1 where ω∣p\omega|_p denotes the conditioned state.

theorem

Conditioned state ω∣p(q)=0\omega|_p(q) = 0 for p⋅q=0p \cdot q = 0

Let EE be a Jordan order unit space. Let p∈Ep \in E be a Jordan projection and ω\omega be a state on EE such that ω(p)>0\omega(p) > 0. Suppose the quadratic representation UpU_p is a positive map. If q∈Eq \in E is Jordan-orthogonal to pp (that is, p⋅q=0p \cdot q = 0), then the conditioned state ω∣p\omega|_p evaluated at qq is zero, i.e., ω∣p(q)=0\omega|_p(q) = 0. Here, the conditioned state ω∣p\omega|_p is defined as the functional x↦ω(Upx)ω(p)x \mapsto \frac{\omega(U_p x)}{\omega(p)}.

theorem

Conditioning on a Jordan projection pp assigns zero probability to 1−p1 - p

Let EE be a Jordan order unit space and p∈Ep \in E be a Jordan projection. Let ω\omega be a state on EE such that ω(p)>0\omega(p) > 0. Suppose the quadratic representation UpU_p of pp is a positive map (i.e., x≥0  ⟹  Upx≥0x \ge 0 \implies U_p x \ge 0). Then the state conditioned on pp, defined by the map x↦ω(Upx)ω(p)x \mapsto \frac{\omega(U_p x)}{\omega(p)}, assigns the value 00 to the algebraic complement 1−p1 - p.

definition

Conditioning a state ω\omega on a Jordan projection pp given quadratic positivity

Given a Jordan projection pp in a Jordan order unit space EE and a state ω∈S(R,E)\omega \in \mathcal{S}(\mathbb{R}, E) such that ω(p)>0\omega(p) > 0, if EE satisfies the condition `IsQuadraticallyPositive` (which ensures that the quadratic representation UpU_p of any projection is a positive map), then the conditioned state ω∣p∈S(R,E)\omega|_p \in \mathcal{S}(\mathbb{R}, E) is defined as the unital positive linear map: x↦ω(Upx)ω(p)x \mapsto \frac{\omega(U_p x)}{\omega(p)} where UpU_p denotes the quadratic representation of the projection pp.

theorem

Evaluation of the Conditioned State ω∣p(x)=ω(Upx)ω(p)\omega|_p(x) = \frac{\omega(U_p x)}{\omega(p)}

Let EE be a Jordan order unit space and let p∈Ep \in E be a Jordan projection. Assume EE is quadratically positive. For any state ω\omega on EE such that ω(p)>0\omega(p) > 0 and any element x∈Ex \in E, the state conditioned on pp (denoted by `conditionOfQuadraticPositive`) evaluates to: ω∣p(x)=ω(Upx)ω(p) \omega|_p(x) = \frac{\omega(U_p x)}{\omega(p)} where UpU_p is the quadratic representation of the projection pp.