Bounded Borel functions on the plane #
Combinations of finite measures on the plane and the transfer principle #
Transfer principle on the plane: a combination vanishing on all compactly supported continuous functions vanishes on all bounded Borel functions.
Multiplying the test function by a fixed bounded Borel function #
The measure H⁺ dμ.
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- CommutingRepetition.BorelCalc.IsCombo2.wd2 μ H = μ.withDensity fun (p : ℝ × ℝ) => ↑(H p).toNNReal
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The polarized form and the joint calculus #
The quadratic form Q2 F ξ = ∫ F dνP_ξ.
Equations
- CommutingRepetition.BorelCalc.Q2 E₁ E₂ h₁ h₂ hc F ξ = ↑(∫ (p : ℝ × ℝ), F p ∂CommutingRepetition.BorelCalc.νP E₁ E₂ h₁ h₂ hc ξ)
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The polarized form.
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- One or more equations did not get rendered due to their size.
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Boundedness #
The polarized form as a bounded sesquilinear map.
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- One or more equations did not get rendered due to their size.
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The joint Borel functional calculus #
The joint Borel functional calculus F(E₁, E₂) for a bounded Borel F : ℝ² → ℝ
(junk value 0 otherwise).
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- One or more equations did not get rendered due to their size.
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On bounded continuous functions the joint calculus is the continuous calculus of
Z = E₁ + i E₂.
One-variable functions #
Linearity #
Multiplicativity #
Step 1: continuous F, Borel G (transfer in G).
Step 2: Borel F and G (transfer in F).
Multiplicativity of the joint Borel calculus.
Norms and order #
‖F(E₁,E₂) ξ‖² = ∫ F² dνP_ξ.
Dominated convergence: uniformly bounded F i → Finf pointwise gives
F i (E₁,E₂) ξ → Finf (E₁,E₂) ξ.
Commutation and membership #
An operator commuting with E₁ and E₂ commutes with the joint calculus.
The joint calculus of a pair in a von Neumann algebra stays in it.
Composition with a one-variable Borel function (continuous F) #
The spectral measure of F(E₁,E₂) at ξ is the pushforward of νP_ξ under F.
Composition: g(F(E₁,E₂)) = (g ∘ F)(E₁,E₂) for continuous bounded F and bounded
Borel g.
Almost-everywhere equal functions give the same operator.
Complex-valued functions #
The complex joint Borel calculus F(E₁,E₂) := (Re F)(E₁,E₂) + i (Im F)(E₁,E₂).
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- One or more equations did not get rendered due to their size.
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Composition for complex G: G(F(E₁,E₂)) = (G ∘ F)(E₁,E₂) (continuous bounded real F,
bounded Borel G).
‖F(E₁,E₂) ξ‖² = ∫ |F|² dνP_ξ for complex F.