Infinite-dimensional operator ridgelet transform

6.3. Gaussian-parameter networks on the sequence space🔗

Let H=\ell^2(\mathbb N) with standard basis (e_j) and Qe_j=q_je_j, q_j>0, \sum_jq_j<\infty; in Lean, H is abstract with a Hilbert basis on which Q is diagonal.

Definition6.3.1
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Definition 1.1.2
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The integral networks F_Q(x)=\int_H\operatorname{ReLU}(\langle a,x\rangle)\,\mathcal N(0,Q)(\mathrm da) and \Phi_Q(x)=\int_H\Phi(\langle a,x\rangle)\,\mathcal N(0,Q)(\mathrm da), and the ReLU coefficient measure of a Gaussian-activation network with coefficient density \gamma: the pushforward of \phi''(b)\gamma(a,c)\,\lambda(\mathrm da,\mathrm dc)\,\mathrm db under (a,c,b)\mapsto(a,c-b).

Lean code for Definition6.3.13 definitions
  • complete
    def OperatorRidgelet.gaussianParameterReLU.{u_1} {H : Type u_1}
      [NormedAddCommGroup H] [InnerProductSpace  H] [MeasurableSpace H]
      (μ : MeasureTheory.Measure H) (x : H) : 
    def OperatorRidgelet.gaussianParameterReLU.{u_1}
      {H : Type u_1} [NormedAddCommGroup H]
      [InnerProductSpace  H]
      [MeasurableSpace H]
      (μ : MeasureTheory.Measure H) (x : H) :
      
    The ReLU network with Gaussian parameters, `F_Q(x) = ∫ ReLU(⟨a,x⟩) 𝒩(0,Q)(da)`, for the
    parameter law `μ = 𝒩(0,Q)` (`eq:gaussian-parameter-networks`). 
  • complete
    def OperatorRidgelet.gaussianParameterGauss.{u_1} {H : Type u_1}
      [NormedAddCommGroup H] [InnerProductSpace  H] [MeasurableSpace H]
      (μ : MeasureTheory.Measure H) (x : H) : 
    def OperatorRidgelet.gaussianParameterGauss.{u_1}
      {H : Type u_1} [NormedAddCommGroup H]
      [InnerProductSpace  H]
      [MeasurableSpace H]
      (μ : MeasureTheory.Measure H) (x : H) :
      
    The Gaussian-activation network with Gaussian parameters,
    `Φ_Q(x) = ∫ Φ(⟨a,x⟩) 𝒩(0,Q)(da)` (`eq:gaussian-parameter-networks`). 
  • complete
    def OperatorRidgelet.hingeCoefficientMeasure.{u_1, u_2} {H : Type u_1}
      [MeasurableSpace H] {Y : Type u_2} [NormedAddCommGroup Y]
      [NormedSpace  Y] (lam : MeasureTheory.Measure (H × ))
      (γ : H ×   Y) : MeasureTheory.VectorMeasure (H × ) Y
    def OperatorRidgelet.hingeCoefficientMeasure.{u_1,
        u_2}
      {H : Type u_1} [MeasurableSpace H]
      {Y : Type u_2} [NormedAddCommGroup Y]
      [NormedSpace  Y]
      (lam : MeasureTheory.Measure (H × ))
      (γ : H ×   Y) :
      MeasureTheory.VectorMeasure (H × ) Y
    The ReLU coefficient measure of a Gaussian-activation network with coefficient density `γ`
    with respect to `λ`: the pushforward of `φ''(b) γ(a,c) λ(da,dc) db` under
    `(a,c,b) ↦ (a, c - b)`. 
Proposition6.3.2
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Definition 2.1.1
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F_Q(x)=\sqrt{\langle Qx,x\rangle/2\pi} (i) and \Phi_Q(x)=(1+\langle Qx,x\rangle)^{-1/2} (ii), which also equals \int_{H\times\mathbb R}\operatorname{ReLU}(\langle a,x\rangle-b)\,\phi''(b)\,\mathcal N(0,Q)(\mathrm da)\,\mathrm db (iii). Neither F_Q (iv) nor \Phi_Q (v) is cylindrical. A Gaussian-activation network with finite coefficient measure is also a ReLU network with the hinge coefficient measure (vi a), which is finite (vi b) with all parameter moments finite (vi c).

Lean code for Proposition6.3.28 theorems
  • complete
    theorem OperatorRidgelet.Paper.ex_gaussian_parameter_i.{u_1} {H : Type u_1}
      [NormedAddCommGroup H] [InnerProductSpace  H] [CompleteSpace H]
      [SecondCountableTopology H] [MeasurableSpace H] [BorelSpace H]
      {Q : H →L[] H} (e : HilbertBasis   H) (q :   )
      (hq :  (j : ), 0 < q j) (hqs : Summable q)
      (hQe :  (j : ), Q (e j) = q j  e j) (μ : MeasureTheory.Measure H)
      [MeasureTheory.IsProbabilityMeasure μ]
      ( : OperatorRidgelet.IsCenteredGaussian Q μ) (x : H) :
      OperatorRidgelet.gaussianParameterReLU μ x =
        (inner  (Q x) x / (2 * Real.pi))
    theorem OperatorRidgelet.Paper.ex_gaussian_parameter_i.{u_1}
      {H : Type u_1} [NormedAddCommGroup H]
      [InnerProductSpace  H]
      [CompleteSpace H]
      [SecondCountableTopology H]
      [MeasurableSpace H] [BorelSpace H]
      {Q : H →L[] H} (e : HilbertBasis   H)
      (q :   ) (hq :  (j : ), 0 < q j)
      (hqs : Summable q)
      (hQe :  (j : ), Q (e j) = q j  e j)
      (μ : MeasureTheory.Measure H)
      [MeasureTheory.IsProbabilityMeasure μ]
      ( :
        OperatorRidgelet.IsCenteredGaussian Q
          μ)
      (x : H) :
      OperatorRidgelet.gaussianParameterReLU μ
          x =
        (inner  (Q x) x / (2 * Real.pi))
    **Example [ex:gaussian-parameter]** ReLU and Gaussian networks with Gaussian parameters.
    `F_Q(x) = ∫ ReLU(⟨a,x⟩) 𝒩(0,Q)(da) = √(⟨Qx,x⟩/2π)`. 
  • complete
    theorem OperatorRidgelet.Paper.ex_gaussian_parameter_ii.{u_1} {H : Type u_1}
      [NormedAddCommGroup H] [InnerProductSpace  H] [CompleteSpace H]
      [SecondCountableTopology H] [MeasurableSpace H] [BorelSpace H]
      {Q : H →L[] H} (e : HilbertBasis   H) (q :   )
      (hq :  (j : ), 0 < q j) (hqs : Summable q)
      (hQe :  (j : ), Q (e j) = q j  e j) (μ : MeasureTheory.Measure H)
      [MeasureTheory.IsProbabilityMeasure μ]
      ( : OperatorRidgelet.IsCenteredGaussian Q μ) (x : H) :
      OperatorRidgelet.gaussianParameterGauss μ x =
        ((1 + inner  (Q x) x))⁻¹
    theorem OperatorRidgelet.Paper.ex_gaussian_parameter_ii.{u_1}
      {H : Type u_1} [NormedAddCommGroup H]
      [InnerProductSpace  H]
      [CompleteSpace H]
      [SecondCountableTopology H]
      [MeasurableSpace H] [BorelSpace H]
      {Q : H →L[] H} (e : HilbertBasis   H)
      (q :   ) (hq :  (j : ), 0 < q j)
      (hqs : Summable q)
      (hQe :  (j : ), Q (e j) = q j  e j)
      (μ : MeasureTheory.Measure H)
      [MeasureTheory.IsProbabilityMeasure μ]
      ( :
        OperatorRidgelet.IsCenteredGaussian Q
          μ)
      (x : H) :
      OperatorRidgelet.gaussianParameterGauss
          μ x =
        ((1 + inner  (Q x) x))⁻¹
    **Example [ex:gaussian-parameter]** ReLU and Gaussian networks with Gaussian parameters.
    `Φ_Q(x) = ∫ Φ(⟨a,x⟩) 𝒩(0,Q)(da) = (1 + ⟨Qx,x⟩)^{-1/2}`. 
  • complete
    theorem OperatorRidgelet.Paper.ex_gaussian_parameter_iii.{u_1} {H : Type u_1}
      [NormedAddCommGroup H] [InnerProductSpace  H] [CompleteSpace H]
      [SecondCountableTopology H] [MeasurableSpace H] [BorelSpace H]
      {Q : H →L[] H} (e : HilbertBasis   H) (q :   )
      (hq :  (j : ), 0 < q j) (hqs : Summable q)
      (hQe :  (j : ), Q (e j) = q j  e j) (μ : MeasureTheory.Measure H)
      [MeasureTheory.IsProbabilityMeasure μ]
      ( : OperatorRidgelet.IsCenteredGaussian Q μ) (x : H) :
      OperatorRidgelet.gaussianParameterGauss μ x =
         (p : H × ),
          LeanRidgelet.relu (inner  p.1 x - p.2) *
            OperatorRidgelet.gaussianActDeriv2
              p.2 μ.prod MeasureTheory.volume
    theorem OperatorRidgelet.Paper.ex_gaussian_parameter_iii.{u_1}
      {H : Type u_1} [NormedAddCommGroup H]
      [InnerProductSpace  H]
      [CompleteSpace H]
      [SecondCountableTopology H]
      [MeasurableSpace H] [BorelSpace H]
      {Q : H →L[] H} (e : HilbertBasis   H)
      (q :   ) (hq :  (j : ), 0 < q j)
      (hqs : Summable q)
      (hQe :  (j : ), Q (e j) = q j  e j)
      (μ : MeasureTheory.Measure H)
      [MeasureTheory.IsProbabilityMeasure μ]
      ( :
        OperatorRidgelet.IsCenteredGaussian Q
          μ)
      (x : H) :
      OperatorRidgelet.gaussianParameterGauss
          μ x =
         (p : H × ),
          LeanRidgelet.relu
              (inner  p.1 x - p.2) *
            OperatorRidgelet.gaussianActDeriv2
              p.2 μ.prod MeasureTheory.volume
    **Example [ex:gaussian-parameter]** ReLU and Gaussian networks with Gaussian parameters.
    `Φ_Q(x) = ∫∫ ReLU(⟨a,x⟩ - b) φ''(b) 𝒩(0,Q)(da) db` with `φ''(b) = (b² - 1) e^{-b²/2}`. 
  • complete
    theorem OperatorRidgelet.Paper.ex_gaussian_parameter_iv.{u_1} {H : Type u_1}
      [NormedAddCommGroup H] [InnerProductSpace  H] [CompleteSpace H]
      [SecondCountableTopology H] [MeasurableSpace H] [BorelSpace H]
      {Q : H →L[] H} (e : HilbertBasis   H) (q :   )
      (hq :  (j : ), 0 < q j) (hqs : Summable q)
      (hQe :  (j : ), Q (e j) = q j  e j) (μ : MeasureTheory.Measure H)
      [MeasureTheory.IsProbabilityMeasure μ]
      ( : OperatorRidgelet.IsCenteredGaussian Q μ) :
      ¬OperatorRidgelet.IsCylindrical
          (OperatorRidgelet.gaussianParameterReLU μ)
    theorem OperatorRidgelet.Paper.ex_gaussian_parameter_iv.{u_1}
      {H : Type u_1} [NormedAddCommGroup H]
      [InnerProductSpace  H]
      [CompleteSpace H]
      [SecondCountableTopology H]
      [MeasurableSpace H] [BorelSpace H]
      {Q : H →L[] H} (e : HilbertBasis   H)
      (q :   ) (hq :  (j : ), 0 < q j)
      (hqs : Summable q)
      (hQe :  (j : ), Q (e j) = q j  e j)
      (μ : MeasureTheory.Measure H)
      [MeasureTheory.IsProbabilityMeasure μ]
      ( :
        OperatorRidgelet.IsCenteredGaussian Q
          μ) :
      ¬OperatorRidgelet.IsCylindrical
          (OperatorRidgelet.gaussianParameterReLU
            μ)
    **Example [ex:gaussian-parameter]** ReLU and Gaussian networks with Gaussian parameters.
    `F_Q` is not cylindrical. 
  • complete
    theorem OperatorRidgelet.Paper.ex_gaussian_parameter_v.{u_1} {H : Type u_1}
      [NormedAddCommGroup H] [InnerProductSpace  H] [CompleteSpace H]
      [SecondCountableTopology H] [MeasurableSpace H] [BorelSpace H]
      {Q : H →L[] H} (e : HilbertBasis   H) (q :   )
      (hq :  (j : ), 0 < q j) (hqs : Summable q)
      (hQe :  (j : ), Q (e j) = q j  e j) (μ : MeasureTheory.Measure H)
      [MeasureTheory.IsProbabilityMeasure μ]
      ( : OperatorRidgelet.IsCenteredGaussian Q μ) :
      ¬OperatorRidgelet.IsCylindrical
          (OperatorRidgelet.gaussianParameterGauss μ)
    theorem OperatorRidgelet.Paper.ex_gaussian_parameter_v.{u_1}
      {H : Type u_1} [NormedAddCommGroup H]
      [InnerProductSpace  H]
      [CompleteSpace H]
      [SecondCountableTopology H]
      [MeasurableSpace H] [BorelSpace H]
      {Q : H →L[] H} (e : HilbertBasis   H)
      (q :   ) (hq :  (j : ), 0 < q j)
      (hqs : Summable q)
      (hQe :  (j : ), Q (e j) = q j  e j)
      (μ : MeasureTheory.Measure H)
      [MeasureTheory.IsProbabilityMeasure μ]
      ( :
        OperatorRidgelet.IsCenteredGaussian Q
          μ) :
      ¬OperatorRidgelet.IsCylindrical
          (OperatorRidgelet.gaussianParameterGauss
            μ)
    **Example [ex:gaussian-parameter]** ReLU and Gaussian networks with Gaussian parameters.
    `Φ_Q` is not cylindrical. 
  • complete
    theorem OperatorRidgelet.Paper.ex_gaussian_parameter_vi_a.{u_1, u_2}
      {H : Type u_1} [NormedAddCommGroup H] [InnerProductSpace  H]
      [MeasurableSpace H] [BorelSpace H] {Y : Type u_2}
      [NormedAddCommGroup Y] [InnerProductSpace  Y] [CompleteSpace Y]
      (lam : MeasureTheory.Measure (H × )) [MeasureTheory.SigmaFinite lam]
      (γ : H ×   Y) ( : MeasureTheory.Integrable γ lam)
      (hmom :
         (k : ),
          MeasureTheory.Integrable
            (fun θ => (1 + θ.1 + |θ.2|) ^ k * γ θ) lam) :
      OperatorRidgelet.integralNetworkDensity
          (fun t => (OperatorRidgelet.gaussianFun t)) lam γ =
        OperatorRidgelet.integralNetwork (fun t => (LeanRidgelet.relu t))
          (OperatorRidgelet.hingeCoefficientMeasure lam γ)
    theorem OperatorRidgelet.Paper.ex_gaussian_parameter_vi_a.{u_1,
        u_2}
      {H : Type u_1} [NormedAddCommGroup H]
      [InnerProductSpace  H]
      [MeasurableSpace H] [BorelSpace H]
      {Y : Type u_2} [NormedAddCommGroup Y]
      [InnerProductSpace  Y]
      [CompleteSpace Y]
      (lam : MeasureTheory.Measure (H × ))
      [MeasureTheory.SigmaFinite lam]
      (γ : H ×   Y)
      ( : MeasureTheory.Integrable γ lam)
      (hmom :
         (k : ),
          MeasureTheory.Integrable
            (fun θ =>
              (1 + θ.1 + |θ.2|) ^ k * γ θ)
            lam) :
      OperatorRidgelet.integralNetworkDensity
          (fun t =>
            (OperatorRidgelet.gaussianFun t))
          lam γ =
        OperatorRidgelet.integralNetwork
          (fun t => (LeanRidgelet.relu t))
          (OperatorRidgelet.hingeCoefficientMeasure
            lam γ)
    **Example [ex:gaussian-parameter]** ReLU and Gaussian networks with Gaussian parameters.  A
    Gaussian-activation network with finite coefficient measure `γ λ` (with all parameter moments
    finite) is the ReLU network with the coefficient measure `Γ' = (a,c,b) ↦ (a, c-b)`-pushforward
    of `φ''(b) γ(a,c) λ(da,dc) db`. 
  • complete
    theorem OperatorRidgelet.Paper.ex_gaussian_parameter_vi_b.{u_1, u_2}
      {H : Type u_1} [NormedAddCommGroup H] [InnerProductSpace  H]
      [MeasurableSpace H] {Y : Type u_2} [NormedAddCommGroup Y]
      [InnerProductSpace  Y] [CompleteSpace Y]
      (lam : MeasureTheory.Measure (H × )) [MeasureTheory.SigmaFinite lam]
      (γ : H ×   Y) ( : MeasureTheory.Integrable γ lam)
      (hmom :
         (k : ),
          MeasureTheory.Integrable
            (fun θ => (1 + θ.1 + |θ.2|) ^ k * γ θ) lam) :
      MeasureTheory.IsFiniteMeasure
        (OperatorRidgelet.hingeCoefficientMeasure lam γ).variation
    theorem OperatorRidgelet.Paper.ex_gaussian_parameter_vi_b.{u_1,
        u_2}
      {H : Type u_1} [NormedAddCommGroup H]
      [InnerProductSpace  H]
      [MeasurableSpace H] {Y : Type u_2}
      [NormedAddCommGroup Y]
      [InnerProductSpace  Y]
      [CompleteSpace Y]
      (lam : MeasureTheory.Measure (H × ))
      [MeasureTheory.SigmaFinite lam]
      (γ : H ×   Y)
      ( : MeasureTheory.Integrable γ lam)
      (hmom :
         (k : ),
          MeasureTheory.Integrable
            (fun θ =>
              (1 + θ.1 + |θ.2|) ^ k * γ θ)
            lam) :
      MeasureTheory.IsFiniteMeasure
        (OperatorRidgelet.hingeCoefficientMeasure
            lam γ).variation
    **Example [ex:gaussian-parameter]** ReLU and Gaussian networks with Gaussian parameters.  The
    ReLU coefficient measure `Γ'` of a Gaussian-activation network with finite coefficient measure
    is finite. 
  • complete
    theorem OperatorRidgelet.Paper.ex_gaussian_parameter_vi_c.{u_1, u_2}
      {H : Type u_1} [NormedAddCommGroup H] [InnerProductSpace  H]
      [MeasurableSpace H] {Y : Type u_2} [NormedAddCommGroup Y]
      [InnerProductSpace  Y] [CompleteSpace Y]
      (lam : MeasureTheory.Measure (H × )) [MeasureTheory.SigmaFinite lam]
      (γ : H ×   Y) ( : MeasureTheory.Integrable γ lam)
      (hmom :
         (k : ),
          MeasureTheory.Integrable
            (fun θ => (1 + θ.1 + |θ.2|) ^ k * γ θ) lam)
      (k : ) :
      ∫⁻ (θ : H × ),
          ENNReal.ofReal
            ((1 + θ.1 + |θ.2|) ^
              k) (OperatorRidgelet.hingeCoefficientMeasure lam
              γ).variation <
        
    theorem OperatorRidgelet.Paper.ex_gaussian_parameter_vi_c.{u_1,
        u_2}
      {H : Type u_1} [NormedAddCommGroup H]
      [InnerProductSpace  H]
      [MeasurableSpace H] {Y : Type u_2}
      [NormedAddCommGroup Y]
      [InnerProductSpace  Y]
      [CompleteSpace Y]
      (lam : MeasureTheory.Measure (H × ))
      [MeasureTheory.SigmaFinite lam]
      (γ : H ×   Y)
      ( : MeasureTheory.Integrable γ lam)
      (hmom :
         (k : ),
          MeasureTheory.Integrable
            (fun θ =>
              (1 + θ.1 + |θ.2|) ^ k * γ θ)
            lam)
      (k : ) :
      ∫⁻ (θ : H × ),
          ENNReal.ofReal
            ((1 + θ.1 + |θ.2|) ^
              k) (OperatorRidgelet.hingeCoefficientMeasure
              lam γ).variation <
        
    **Example [ex:gaussian-parameter]** ReLU and Gaussian networks with Gaussian parameters.  The
    ReLU coefficient measure `Γ'` of a Gaussian-activation network with finite coefficient measure
    has all parameter moments finite. 
Proof for Proposition 6.3.2
uses 0

For fixed x, \langle a,x\rangle is centred Gaussian with variance v=\langle Qx,x\rangle, and \mathbb EZ_+=\sqrt{v/2\pi}, \mathbb Ee^{-Z^2/2}=(1+v)^{-1/2} for Z\sim\mathcal N(0,v); the hinge representation of Lemma 6.1.6 with Fubini gives (iii) and (vi), and a nonzero vector in the kernel of a finite-rank map would give the same value as x=0, contradicting injectivity of Q.

Corollary6.3.3
Statement uses 4
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Theorem 5.1.6
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Let a_1,\dots,a_N be independent with law \mathcal N(0,Q) and F_{Q,N}(x)=\frac1N\sum_{j=1}^N\operatorname{ReLU}(\langle a_j,x\rangle). Then for every compact K\subset H, \mathbb E\|F_{Q,N}-F_Q\|_{C(K)}\le8R_K\sqrt{\operatorname{tr}Q}/\sqrt N.

Lean code for Corollary6.3.31 theorem
  • complete
    theorem OperatorRidgelet.Paper.cor_relu_discretization.{u_1} {H : Type u_1}
      [NormedAddCommGroup H] [InnerProductSpace  H] [CompleteSpace H]
      [SecondCountableTopology H] [MeasurableSpace H] [BorelSpace H]
      {Q : H →L[] H} (hQ : OperatorRidgelet.IsTraceClassCovariance Q)
      (μ : MeasureTheory.Measure H) [MeasureTheory.IsProbabilityMeasure μ]
      ( : OperatorRidgelet.IsCenteredGaussian Q μ) (K : Set H)
      (hK : IsCompact K) (n : ) (hn : 0 < n) :
       (θ : Fin n  H × ),
          OperatorRidgelet.compactSupNorm K fun x =>
            OperatorRidgelet.sampledNetwork
                (fun t => (LeanRidgelet.relu t)) 1 (fun x => 1) θ x -
              (OperatorRidgelet.gaussianParameterReLU μ
                  x) OperatorRidgelet.sampleLaw n
            (MeasureTheory.Measure.map (fun a => (a, 0)) μ) 
        8 * OperatorRidgelet.compactRadius K *
            (OperatorRidgelet.traceOf Q) /
          n
    theorem OperatorRidgelet.Paper.cor_relu_discretization.{u_1}
      {H : Type u_1} [NormedAddCommGroup H]
      [InnerProductSpace  H]
      [CompleteSpace H]
      [SecondCountableTopology H]
      [MeasurableSpace H] [BorelSpace H]
      {Q : H →L[] H}
      (hQ :
        OperatorRidgelet.IsTraceClassCovariance
          Q)
      (μ : MeasureTheory.Measure H)
      [MeasureTheory.IsProbabilityMeasure μ]
      ( :
        OperatorRidgelet.IsCenteredGaussian Q
          μ)
      (K : Set H) (hK : IsCompact K) (n : )
      (hn : 0 < n) :
       (θ : Fin n  H × ),
          OperatorRidgelet.compactSupNorm K
            fun x =>
            OperatorRidgelet.sampledNetwork
                (fun t =>
                  (LeanRidgelet.relu t))
                1 (fun x => 1) θ x -
              (OperatorRidgelet.gaussianParameterReLU
                  μ
                  x) OperatorRidgelet.sampleLaw
            n
            (MeasureTheory.Measure.map
              (fun a => (a, 0)) μ) 
        8 * OperatorRidgelet.compactRadius K *
            (OperatorRidgelet.traceOf Q) /
          n
    **Corollary [cor:relu-discretization]** Discretization of the Gaussian-parameter ReLU
    network.  For `a_1, …, a_n` independent with law `𝒩(0,Q)` (the samples `θ_j = (a_j, 0)` of the
    law `ι_# 𝒩(0,Q)`, `ι(a) = (a, 0)`) and `F_{Q,n}(x) = n⁻¹ ∑_j ReLU(⟨a_j,x⟩)` (the sampled network
    `eq:polar-network` with `V = 1` and phase `1`), every compact `K ⊆ H` satisfies
    `E‖F_{Q,n} - F_Q‖_{C(K)} ≤ 8 R_K √(tr Q) / √n`. 
Proof for Corollary 6.3.3
uses 0

Apply Theorem 5.1.6 with V=1, c=0, \beta(0)=0, \operatorname{Lip}(\beta)=1, and M_2^2=\mathbb E\|a\|^2=\operatorname{tr}Q.