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Functional BvM limits and credible-set calibration

1 · Prerequisites

2 · Summary

Objective

This page develops scalar functional BvM limits and credible-interval calibration in Gaussian white noise, including the nonlinear delta-method condition. It defines the multiscale coefficient space and the type-S and type-H density prior interfaces, then proves the source-specific density weak BvM theorems and their CDF and multiscale credible-band consequences, with the required sampling-process and Gaussian norm-quantile limits. It records the exact smoothness, positivity, topology, centering, and rate assumptions used in each result.

For type S, local quotient-likelihood contraction, wavelet composition and projection estimates, and posterior Laplace bounds prove the weak BvM under both approved coefficient-prior regimes. For type H, the Dirichlet posterior and normalized-Gamma concentration give a direct conjugate proof. The resulting empirical-center credible bands have asymptotically exact coverage; the stated additional coefficient smoothness and undersmoothing assumptions give the diameter bound.

3 · Logical flowchart

4 · Definitions, theorems and proofs

DefinitionDefinition: AI-adaptedProof: Not applicablejudge pass (gpt-6-luna)Open item page →

Little-o multiscale coefficient space M0(w)

Definition

Use the wavelet coefficient levels (l,k) and multiplicities ∣Kl∣=2l from Logarithmic negative Sobolev spaces for white noise. The same coefficient-space definition applies to the Haar system used for type-H histograms: detail levels l≥0 have 2l coefficients, and the single scaling coefficient is an additional finite coarsest coordinate, included in the norm with weight 1. Finite projections always retain that scaling coordinate; this finite convention does not alter any tail assertion. Let w=(wl) be nondecreasing with wl≥1. Define M(w)={x=(xlk):∥x∥M(w):=sup⁡lmax⁡k∈Kl∣xlk∣wl<∞} and its closed little-o subspace M0(w)={x∈M(w):max⁡k∈Kl∣xlk∣wl⟶0 as l→∞}, with the same norm. Call w admissible when wl/l→∞. The finite coarsest level is included in the norm and does not affect this limit. Elements are coefficient sequences; in particular, they need not be L2 functions. The multiscale coefficient space is separable and has vanishing projection tails ↗ proves that M0(w) is a separable Banach space, that L2 coefficient sequences embed in it, and that finite-level projections converge in its norm.

DefinitionDefinition: AI-adaptedProof: Not applicableOpen item page →

Smooth linear functionals on the white-noise topology

Definition

Fix the real orthonormal wavelet basis and level weights al of Logarithmic negative Sobolev spaces for white noise. For 0≤s<S, define the basis Sobolev space H2s={g∈L2([0,1]):∑l,kal2s∣⟨g,ψlk⟩∣2<∞}. For g∈H2s, s>1/2, and f∈L2([0,1]), define Lg(f)=⟨f,g⟩L2. For x=(xlk)∈H(δ), the intended extension is the coefficient pairing Lg(x)=∑l,kxlk⟨g,ψlk⟩; Smooth functionals extend continuously to the white-noise topology ↗ proves that this series is absolutely convergent and defines a continuous linear functional on H(δ) for every δ>0.

In the white-noise experiment X(n)=f0+n−1/2W, fix δ>1/2 so that the observation is H(δ)-valued; Lg(X(n)) means this continuous pairing with the H(δ)-valued observation. It does not assert that X(n) is an L2 function. The representer is nonzero when g≠0; the corresponding white-noise variance is ∥g∥22.

DefinitionDefinition: AI-adaptedProof: Not applicableOpen item page →

Type-S log-density and type-H histogram prior families

Definition

For type S use a fixed sufficiently regular compactly supported orthonormal multiresolution wavelet basis (ψlk) on [0,1] as in Logarithmic negative Sobolev spaces for white noise, with boundary correction, regularity greater than the truth smoothness α, and ∣Kl∣=2l. The spaces VL spanned by the retained levels l≤L contain constants and have orthonormal scaling bases with uniformly bounded overlap, support diameters at most C2−L, and suprema at most C2L/2; a fixed shift of the scaling-resolution index is absorbed in C. The wavelets likewise have uniformly bounded overlap, support diameters at most C2−l, and suprema at most C2l/2. For an integer m>α, the detail wavelets have vanishing moments through degree m−1, and derivatives through order m satisfy ∥ψlk(q)∥∞≤Cq2l(q+1/2), with uniformly bounded overlap of their supports; the fixed low scaling functions are Cm. These are the sufficiently regular compact multiresolution basis conditions in the source density theorem. For the density-model source results, every truth f0 is a probability density satisfying 0<ρ0≤f0≤D0<∞ for constants ρ0,D0. For n≥3 and smoothness index α>0, let jn and ℓn be the largest integers satisfying 2jn≤n1/(2α+1),2ℓn≤(n/log⁡n)1/(2α+1). Choose one cutoff sequence Ln∈{jn,ℓn} for all n≥3; set any finite Ln for n=1,2, which does not change asymptotic claims.

For a finite wavelet series Tn=∑l≤Ln∑k∈Klσlξlkψlk, define c(Tn)=log⁡∫01eTn(x)dx and the normalized log-density fn(x)=eTn(x)−c(Tn).

The type-S1 family takes IID coefficients ξlk with a continuous density φH for which log⁡φH is Lipschitz, and uses σl=2−l(α+1/2). Its source theorem assumes log⁡f0 has coefficient Hölder regularity α>1 and f0 is bounded above and bounded away from zero.

The type-S2 family takes IID standard-normal coefficients and uses σl=2−l(r+1/2), where α>1/2 and 0<r<α−1/4. Here the truth regime is log⁡f0∈Cα with positive finite density bounds. Equation (24) in the source specifies this prior-parameter range, but its Theorem 3 assumes α>1 for both type-S families. The broader Gaussian truth range α>1/2 is established separately by the local type-S posterior BvM theorem.

For the type-H family, use the Haar basis instead of the regular type-S wavelets: its scaling function is 1 and ψlk=2l/2(1Il+1,2k−1Il+1,2k+1) for l≥0 and 0≤k<2l. The histogram space at resolution L consists of the scaling coordinate and detail levels l<L; all detail coefficients at l≥L vanish. Partition [0,1] into dyadic cells ILn,k of length 2−Ln, draw ω=(ωk)k<2Ln∼Dirichlet⁡(a0,Ln,…,a2Ln−1,Ln), and set fn=2Lnωk on cell ILn,k. The source assumptions are c12−Lna≤ak,Ln≤c2 for fixed positive a,c1,c2, and f0∈Cα for 1/2<α≤1, together with the common positive finite density bounds above. The posterior asymptotic conclusions for these families are separate results.

Here Cψα denotes the coefficient class with norm ∥g∥Cψα:=sup⁡l,k2l(α+1/2)∣⟨g,ψlk⟩∣. For sufficiently regular standard wavelets this is the usual Hölder scale (with the usual Zygmund interpretation at integer smoothness).

LemmaStatement: AI-adaptedProof: AI-adaptedOpen item page →

The multiscale coefficient space is separable and has vanishing projection tails

Statement

For every weight sequence in Little-o multiscale coefficient space M0(w), M0(w) is a separable Banach space. If PJ retains exactly the coefficients at levels l≤J, then ∥PJx∥M(w)≤∥x∥M(w) and ∥x−PJx∥M(w)→0 for each x∈M0(w). Every square-summable coefficient sequence belongs to M0(w).

Facts & Assumptions

Given: The finite level sets Kl, weights wl≥1, and the vanishing-tail definition of M0(w).

[F1]

Little-o multiscale coefficient space M0(w): the detail norm is D(x)=sup⁡lwl−1max⁡k∈Kl∣xlk∣. Without an extra scaling coordinate the norm is D(x); in the Haar convention, writing x∗ for that coordinate, it is max⁡(∣x∗∣,D(x)). Membership in M0(w) means the normalized detail maximum tends to zero. As in that definition, every PJ retains the finite coarsest coordinates, including x∗ when present.

Proof

1.1F1givenchoosealgebra

Let (x(m)) be Cauchy in M0(w). Each coordinate is Cauchy because ∣xlk(m)−xlk(n)∣≤wl∥x(m)−x(n)∥M(w). In the Haar case also ∣x∗(m)−x∗(n)∣≤∥x(m)−x(n)∥M(w). Let xlk and, when present, x∗ be the scalar limits. The uniform Cauchy bound passes to every finite collection of coordinates and then to the supremum, so x(m)→x in the weighted supremum norm. To see x∈M0(w), fix ε>0, choose m with ∥x−x(m)∥M(w)<ε, then choose J so the normalized tail of x(m) is below ε; for l>J the normalized tail of x is at most 2ε. Thus M0(w) is complete.

1.2F1givenchoosealgebra

Finite-support sequences with rational coordinates are countable and dense: first choose J to make the tail of any x∈M0(w) small, then approximate its finitely many coordinates through level J, including the scaling coordinate when present, by rationals. Hence M0(w) is separable. The formula for the norm shows PJ is a contraction, and the defining tail limit gives ∥x−PJx∥M(w)→0.

2.1F1givenalgebra∎

If x∈ℓ2, then wl≥1 implies wl−1max⁡k∣xlk∣≤(∑k∣xlk∣2)1/2. The right side tends to zero because its squares are level blocks of a convergent nonnegative series. Its supremum and the absolute scaling coordinate, when present, are at most ∥x∥ℓ2, so x∈M0(w).

LemmaStatement: AI-adaptedProof: AI-adaptedjudge pass (gpt-6-luna)Open item page →

The multiscale primitive map is continuous into C[0,1]

Statement

Let (ψlk) be a compactly supported wavelet basis of Logarithmic negative Sobolev spaces for white noise. The Haar basis with its finite scaling coordinate, as specified in Little-o multiscale coefficient space M0(w), is also allowed. Assume each level-l wavelet for l≥l0 has zero integral, uniformly bounded overlap, support length at most C02−l, and ∥ψlk∥1≤C02−l/2. Let M0(w) be as in Little-o multiscale coefficient space M0(w), and suppose Sw:=∑l≥l0wl2−l/2<∞. For x∈M0(w) define Jx(t):=∑l,kxlk⟨1[0,t],ψlk⟩L2,0≤t≤1. Then this series converges absolutely and uniformly in t, Jx∈C([0,1]), and ∥Jx−Jy∥∞≤CSw∥x−y∥M(w) after adding the finite coarsest-level constant to CSw. If x is the coefficient sequence of f∈L2, then Jx(t)=∫0tf(u) du.

Facts & Assumptions

Given: The wavelet geometry, summability condition, and multiscale space in the Statement.

[F1]

Little-o multiscale coefficient space M0(w): ∥x∥M(w)=sup⁡lwl−1max⁡k∣xlk∣.

[F2]

Logarithmic negative Sobolev spaces for white noise: (ψlk) is a complete orthonormal basis of L2([0,1]); finite orthogonal projections converge in L2.

Proof

1.1givenalgebra

For fixed t and level l≥l0, a wavelet whose support lies wholly on one side of t contributes zero: it is either disjoint from [0,t] or its entire support is integrated and its mean is zero. Only supports meeting t can contribute. Uniformly bounded overlap bounds their number by a constant, and each coefficient has magnitude at most ∥ψlk∥1≤C02−l/2. Thus sup⁡t∑k∣⟨1[0,t],ψlk⟩∣≤C12−l/2. The finitely many coarsest levels have a finite uniform sum as well.

2.1F1givenstep 1.1algebra

By [F1] and step 1.1, the absolute sum of all terms at levels l≥l0 is at most C1∥x∥M(w)∑l≥l0wl2−l/2, uniformly over t. Its tails tend uniformly to zero because Sw<∞. Each finite-level sum is continuous in t, since t↦∫0tψlk(u)du is continuous for an L1 function. The uniform limit is continuous. Applying the same estimate to x−y proves the stated operator-norm bound.

3.1F2step 2.1algebra∎

If xlk=⟨f,ψlk⟩ for f∈L2, the finite orthogonal projections converge to f in L2 by [F2]. The map f↦∫0tf(u)du=⟨f,1[0,t]⟩ is a continuous L2 functional because ∥1[0,t]∥2≤1. Applying it to the finite projections shows that their coefficient sums converge to ∫0tf, while step 2.1 identifies the same limit with Jx(t).

LemmaStatement: AI-adaptedProof: AI-adaptedjudge pass (gpt-6-luna)Open item page →

Posterior quantiles stabilize under scalar weak convergence

Statement

Let Qn(y,⋅) be data-indexed probability kernels on R, let Q be a fixed law with continuous CDF F, and suppose βBL(Qn(y,⋅),Q)→0 in probability. Fix 0<u<1 and let q=qu(Q):=inf⁡{r∈Q:Q((−∞,r])≥u}, using the canonical rational embedding. Assume F is strictly increasing on some open interval containing q. Define qu(Qn(y,⋅)) by the same convention. Then qu(Qn)→q in probability. The local strict-increase hypothesis permits CDFs, such as norms of nonnegative random elements, that are constant on part of R.

Facts & Assumptions

Given: The data-indexed kernels, fixed Q, and u∈(0,1) in the Statement; βBL(Qn,Q)=sup⁡{∣∫h dQn−∫h dQ∣:∥h∥∞≤1,Lip⁡(h)≤1}.

[F1]

Posterior quantiles are measurable and bracket their probability level: the lower quantile is the real infimum of {r∈Q:Q((−∞,r])≥u} and its CDF satisfies Q((−∞,q))≤u≤Q((−∞,q]).

[F2]

Continuity from above when one set has finite measure: probabilities of decreasing measurable sets with finite first measure converge to the probability of their intersection.

[A1]

The limiting CDF is continuous on R and strictly increasing on an open interval containing qu(Q).

Proof

1.1A1F2givenalgebra

Fix x∈R and η>0. Choose 0<δ<min⁡(1,η). The piecewise-linear ramps that fall from 1 to 0 on [x−δ,x] and on [x,x+δ] bound 1(−∞,x] below and above. Multiplying each ramp by δ makes its sup norm and Lipschitz constant at most 1. Comparing the lower and upper ramps under Qn with their integrals under Q gives ∣Qn((−∞,x])−F(x)∣≤δ−1βBL(Qn,Q)+Q([x−δ,x+δ]). By [A1], Q({x})=0; [F2] then gives Q([x−δ,x+δ])→0 as δ↓0. First choose δ small and then let n→∞; this proves Qn((−∞,x])→F(x) in probability.

2.1A1F1step 1.1algebra∎

Write q=qu(Q) as in [F1]. Since [A1] makes F continuous, the CDF bracket in [F1] gives F(q)=u. For every sufficiently small ε>0, strict increase near q then gives F(q−ε)<u<F(q+ε). Step 1.1 at these two points implies, with probability tending to one, Qn((−∞,q−ε])<u<Qn((−∞,q+ε]). By monotonicity, no rational at or below q−ε is in the defining set for qu(Qn), while every rational above q+ε belongs to it. Its infimum therefore lies in [q−ε,q+ε]. Since arbitrarily small such ε are available, the quantiles converge in probability.

LemmaStatement: AI-adaptedProof: AI-adaptedOpen item page →

Smooth functionals extend continuously to the white-noise topology

Statement

Let H(δ) be the coefficient Hilbert space of Logarithmic negative Sobolev spaces for white noise, with weights wl=al−1(log⁡al)−2δ. If g∈H2s for some s>1/2, then the pairing Lg(x)=∑l,kxlkglk, where glk=⟨g,ψlk⟩, converges absolutely for every x∈H(δ) and is continuous, with ∣Lg(x)∣≤Cs,δ∥g∥H2s∥x∥H(δ). On L2([0,1]) this extension agrees with the usual inner product ⟨f,g⟩L2.

Facts & Assumptions

Given: The wavelet coefficient weights and the Sobolev coefficient norm in the Statement.

[F1]

Smooth linear functionals on the white-noise topology: g∈H2s means ∑l,kal2s∣glk∣2<∞, and its pairing with an L2 function is the L2 inner product.

[F2]

Logarithmic negative Sobolev spaces for white noise: ∥x∥H(δ)2=∑l,kwl∣xlk∣2, where wl=al−1(log⁡al)−2δ and the coarsest level has finite multiplicity.

Proof

1.1F1F2givenalgebra

Since s>1/2, the level factor al1−2s(log⁡al)2δ is bounded: it tends to zero as al→∞, because a positive power of al dominates every fixed power of log⁡al, and the finitely many coarsest levels have finite weights. Thus wl−1≤Cs,δ2al2s after increasing a finite constant.

2.1F1F2step 1.1algebra

Weighted Cauchy–Schwarz gives ∑l,k∣xlkglk∣≤(∑l,kwl∣xlk∣2)1/2(∑l,kwl−1∣glk∣2)1/2≤Cs,δ∥x∥H(δ)∥g∥H2s. The same bound applied to x−y proves continuity and absolute convergence of the series.

3.1F1F2step 2.1algebra∎

If x is the coefficient sequence of f∈L2, its finite orthonormal projections converge to f in L2 because (ψlk) is a complete orthonormal basis. Their inner products with g are the finite partial sums of the displayed pairing, and converge to ⟨f,g⟩L2 by continuity of the inner product. Step 2.1 identifies the same limit with Lg(x).

LemmaStatement: AI-adaptedProof: AI-adaptedOpen item page →

Finite type-S and type-H prior draws are L2 probability densities

Statement

Every finite type-S draw and every type-H draw in Type-S log-density and type-H histogram prior families is a well-defined nonnegative L2([0,1]) probability density.

Facts & Assumptions

Given: A finite type-S coefficient array or a type-H Dirichlet vector, and the bounded finite-level wavelet basis and normalized prior constructions of Type-S log-density and type-H histogram prior families.

[F1]

Type-S log-density and type-H histogram prior families: type S sets f=eT−c(T) for a finite bounded wavelet sum T, with c(T)=log⁡∫01eT; type H sets f=2Lωk on dyadic cells of length 2−L, where ωk≥0 and ∑kωk=1.

Proof

1.1F1givenalgebra

For a type-S draw, boundedness of the finite wavelet sum gives M=∥T∥∞<∞, hence e−M≤eT(x)≤eM on [0,1]. Therefore 0<e−M≤∫01eT(x)dx≤eM<∞, so c(T) is finite and f=eT−c(T) is positive and integrates to one. The same bounds make f bounded, so f∈L2([0,1]).

2.1F1givenalgebra∎

For type H, each dyadic cell has length 2−L, so ∫01f(x)dx=∑k<2L2Lωk2−L=∑kωk=1. Also ∥f∥22=2L∑kωk2≤2L(∑kωk)2=2L<∞, since all weights are nonnegative. Thus every type-H draw is a nonnegative L2 probability density.

LemmaStatement: AI-adaptedProof: AI-adaptedjudge pass (gpt-6-luna)Open item page →

Finite-projection convergence and posterior tail control imply weak BvM

Statement

Let Qn be data-indexed probability measures on M0(w) and let G be a fixed probability measure on this space. For the projections PJ of The multiscale coefficient space is separable and has vanishing projection tails, suppose that for every fixed J, βBL(Qn∘PJ−1,G∘PJ−1)→0 in probability, and that for every ε,η>0, lim⁡J→∞lim sup⁡n→∞P{Qn(∥x−PJx∥M(w)>ε)>η}=0. Then βBL(Qn,G)→0 in probability.

Facts & Assumptions

Given: The M0(w) norm and projections, the bounded-Lipschitz metric, and the finite-projection and posterior-tail assumptions in the Statement.

[F1]

Little-o multiscale coefficient space M0(w): M0(w) has the weighted supremum norm and consists of coefficient sequences whose normalized level maxima vanish.

[F2]

The multiscale coefficient space is separable and has vanishing projection tails: PJx→x in M0(w) for every x∈M0(w).

[F3]

Continuity from above when one set has finite measure: if measurable sets decrease and the first has finite measure, their measures decrease to the measure of their intersection.

Proof

1.1F1givenalgebra

For any probability measure Q on M0(w) and any bounded 1-Lipschitz function h, ∣h(x)−h(PJx)∣≤min⁡(2,∥x−PJx∥M(w)). Splitting at ε>0 and taking the supremum over such h gives βBL(Q,Q∘PJ−1)≤ε+2Q(∥x−PJx∥M(w)>ε). Applying this to Qn and G, then using the triangle inequality, bounds βBL(Qn,G) by the two projection errors and the fixed-J distance between projected laws.

2.1F2F3givenstep 1.1algebra∎

For each x∈M0(w), [F2] gives ∥x−PJx∥M(w)→0. Thus the events {x:∥x−PJx∥M(w)>ε} decrease to the empty set, and [F3] makes their G-probabilities tend to zero. Given any target error, first choose ε small, then choose J large so this G-tail and the limiting posterior-tail probability are small; for that fixed J, the projected-law distance tends to zero in probability by assumption. Step 1.1 then implies βBL(Qn,G)→0 in probability.

TheoremStatement: Literature-sourcedProof: AI-adaptedOpen item page →

Linear-functional BvM limit and credible-interval calibration

Statement

Use the product-prior white-noise model and supplied posterior kernel of Weak nonparametric Bernstein–von Mises theorem for product priors, including its wavelet-basis, coefficient-density, truth, and countable-choice hypotheses. Let g∈H2s for some s>1/2, with g≠0, and put σg=∥g∥2. Let Qn be the posterior law of Lg(f) and let Cn,α=[qα/2(Qn),q1−α/2(Qn)],0<α<1. Then βBL,R ⁣(Qn∘[u↦n(u−Lg(X(n)))]−1,N(0,σg2))⟶0 in Pf0(n)-probability. The interval Cn,α is posterior credible at level 1−α, and its frequentist coverage satisfies Pf0(n){Lg(f0)∈Cn,α}⟶1−α.

Facts & Assumptions

Given: The white-noise experiment, product prior, posterior kernel, basis, density and truth assumptions of Weak nonparametric Bernstein–von Mises theorem for product priors, together with g≠0, g∈H2s, s>1/2, and 0<α<1.

[F1]

Weak nonparametric Bernstein–von Mises theorem for product priors: for every δ>1/2, the posterior law of n(f−X(n)) converges in bounded-Lipschitz distance in H(δ) to the canonical white-noise law N in Pf0(n)-probability. Its product-prior construction requires countable choice; the same axiom suffices for the scalar density-normal interface.

[F2]

Smooth functionals extend continuously to the white-noise topology: Lg is a continuous linear functional on H(δ) and agrees with f↦⟨f,g⟩L2 on L2.

[F3]

White noise is a Borel Gaussian law on the negative Sobolev space: the canonical law N is centered Gaussian on H(δ); for the coefficient pairing Lg, its variance is ∑l,k∣glk∣2=∥g∥22.

[F4]

Posterior quantiles stabilize under scalar weak convergence: bounded-Lipschitz convergence in probability to a law with continuous CDF locally strictly increasing at an interior quantile implies convergence in probability of that posterior quantile.

[F5]

Equal-tailed posterior quantile intervals are credible: the equal-tailed interval between posterior quantiles qα/2 and q1−α/2 is graph-measurable and has posterior mass at least 1−α.

[F6]

Density normal laws and square-summable Gaussian series under countable choice: Under countable choice, in its density convention, N(0,1) is defined by its continuous positive density, and N(0,σ2) for σ>0 is its image under x↦σx; change of variables gives a continuous strictly positive density and hence a continuous strictly increasing CDF.

[A1]

The Axiom of Countable Choice (ACω): countable choice is inherited through [F1] for the L2 product-prior construction and also suffices for the density normal-law interface [F6]; no full choice is used below.

Proof

1.1A1F1F2F3algebra

Fix δ>1/2. For every bounded 1-Lipschitz function h:R→R, the composition h∘Lg is bounded by 1 and has Lipschitz constant at most ∥Lg∥H(δ)∗. Rescaling by cg=max⁡(1,∥Lg∥H(δ)∗) makes it an admissible bounded-Lipschitz test on H(δ). Hence the scalar pushforward distance is at most cg times the distance in [F1]. The pushforward of N is N(0,σg2) by [F3], proving the asserted scalar BvM limit.

2.1F4F5F6step 1.1algebra

Translate the posterior law of Lg(f) by Lg(X(n)) and scale by n. By [F4] and the continuous strictly increasing normal CDF from [F6], the two quantiles of this scaled law converge in probability to σgzα/2 and σgz1−α/2, where zu is the u-quantile of N(0,1). Since the affine map is increasing, these are exactly the scaled endpoints of Cn,α−Lg(X(n)). The interval is credible by [F5].

3.1F3F6step 2.1algebra

Under the true white-noise law, n{Lg(X(n))−Lg(f0)}=Lg(W) has exactly the centered normal law N(0,σg2) by [F3]. On the event that both random scaled endpoints in step 2.1 lie within ε of their limits, the event Lg(f0)∈Cn,α is bounded between the corresponding deterministic normal-interval events with endpoints enlarged or contracted by ε. This sandwich uses no independence between the endpoints and the observation. The endpoint event has probability tending to one, and [F6] makes the normal mass of shrinking neighborhoods of the two endpoints tend to zero.

4.1F6step 3.1algebra∎

Letting n→∞ and then ε↓0 in the sandwich of step 3.1 gives limiting coverage Φ(z1−α/2)−Φ(zα/2)=1−α by the definition of the normal quantiles and CDF in [F6].

TheoremStatement: Literature-sourcedProof: AI-adaptedOpen item page →

Nonlinear-functional BvM limit under fast L2 contraction

Statement

Use the white-noise experiment, product prior, and supplied posterior kernel of Weak nonparametric Bernstein–von Mises theorem for product priors, with all its stated basis, coefficient-density, truth, and countable-choice hypotheses. Let Ψ:L2([0,1])→R be Borel measurable. Suppose f0∈L2, and for some g∈H2s, s>1/2, g≠0, C<∞, and ρ>0, ∣Ψ(f0+h)−Ψ(f0)−⟨h,g⟩L2∣≤C∥h∥22whenever ∥h∥2≤ρ. Assume the posterior contracts in L2 at a deterministic radius rn=o(n−1/2), meaning Πn(∥f−f0∥2>rn∣X(n))=oPf0(n)(1). Define the efficient center θn∗:=Ψ(f0)+Lg(X(n)−f0), where the last pairing is the continuous H(δ) extension from Smooth functionals extend continuously to the white-noise topology. Then the posterior law of n{Ψ(f)−θn∗} converges in bounded-Lipschitz distance to N(0,∥g∥22) in Pf0(n)-probability. The equal-tailed posterior interval for Ψ(f) at level 1−α is credible and has frequentist coverage tending to 1−α.

The stipulated radius implies the source's squared-radius condition: with sn=rn2, one has sn=o(n−1/2) and posterior mass inside ∥f−f0∥22≤sn tends to one. However, for g≠0 this radius is incompatible with the imported weak BvM limit. Thus the implication under the retained radius is vacuous; the source's squared-radius condition does not have this incompatibility.

Facts & Assumptions

Given: The product-prior weak BvM model of [F1], the Borel functional Ψ, the stated local quadratic expansion with nonzero Riesz representer g, the posterior L2 radius rn=o(n−1/2), and 0<α<1.

[F1]

Weak nonparametric Bernstein–von Mises theorem for product priors: the posterior law of n(f−X(n)) converges in bounded-Lipschitz distance on H(δ) to the canonical white-noise law for every δ>1/2.

[F2]

Smooth functionals extend continuously to the white-noise topology: Lg extends continuously from L2 to H(δ).

[F3]

White noise is a Borel Gaussian law on the negative Sobolev space: Lg(W) is exactly N(0,∥g∥22) under the true white-noise law.

[F4]

Posterior quantiles stabilize under scalar weak convergence: scalar bounded-Lipschitz convergence to a CDF continuous on R and locally strictly increasing at the target quantile implies quantile convergence.

[F5]

Equal-tailed posterior quantile intervals are credible: equal-tailed posterior quantiles define a measurable credible interval of posterior mass at least 1−α.

[F6]

Density normal laws and square-summable Gaussian series under countable choice: Under countable choice, in its density convention, N(0,1) is defined by its continuous positive density, and N(0,σ2) for σ>0 is its image under x↦σx; change of variables gives a continuous strictly positive density and hence a continuous strictly increasing CDF.

[A1]

The Axiom of Countable Choice (ACω): countable choice supplies the L2 prior construction in [F1] and the density normal-law interface [F6]; no full choice is used below.

Proof

1.1givenalgebra

On the posterior event ∥f−f0∥2≤rn≤ρ, write R(f)=Ψ(f)−Ψ(f0)−Lg(f−f0). The expansion gives n∣R(f)∣≤Cnrn2→0. Outside the event, posterior mass is oPf0(n)(1) by assumption. Hence for every ε>0, Πn(n∣R(f)∣>ε∣X(n))→0 in Pf0(n)-probability.

2.1A1F1F2F3step 1.1algebra

For posterior draws, n{Ψ(f)−θn∗}=nLg(f−X(n))+nR(f). For cg=max⁡(1,∥Lg∥), composing a bounded 1-Lipschitz scalar test with Lg and dividing by cg gives an admissible bounded-Lipschitz test on H(δ). Thus the first term has bounded-Lipschitz distance to the pushforward limit at most cg times the distance in [F1]; by [F3] that limit is N(0,∥g∥22). For any bounded 1-Lipschitz test function, replacing the first term by its sum with the remainder changes its posterior integral by at most ε+2Πn(n∣R(f)∣>ε∣X(n)). Step 1.1 and then ε↓0 prove the asserted scalar BvM limit.

3.1F4F5F6step 2.1algebra

Apply [F4] to the centered and scaled posterior law in step 2.1. By [F6], its α/2 and 1−α/2 quantiles converge in probability to ∥g∥2zα/2 and ∥g∥2z1−α/2. Translating and rescaling these quantiles gives the equal-tailed posterior interval for Ψ(f); its credibility follows from [F5].

4.1F3F6step 3.1algebra

Under the true experiment, n{θn∗−Ψ(f0)}=Lg(W) has exactly the law N(0,∥g∥22) by [F3]. The random centered interval endpoints in step 3.1 converge in probability to the corresponding normal quantiles. For any fixed ε>0, on the event that both endpoints are within ε of their limits, coverage is bounded by deterministic normal-interval probabilities with endpoints enlarged or contracted by ε. This argument requires no independence between the endpoints and Lg(W). By [F6], the mass of shrinking endpoint neighborhoods vanishes; letting n→∞ and then ε↓0 gives coverage 1−α.

5.1F1F2F3F6step 2.1givenconstructalgebra∎

To verify the caveat, put Q=N(0,∥g∥22), whose density is bounded by M=(2π∥g∥22)−1/2 by [F6]. Choose 0<a≤1 with 2aM<1/2 and set cn=−nLg(X(n)−f0). For each realized data set, hn(x)=(a−∣x−cn∣)+ is a bounded 1-Lipschitz test. On ∥f−f0∥2≤rn, its value at nLg(f−X(n)) is at least a−n∥g∥2rn, so its posterior integral tends to a in probability. But ∫hn dQ≤2a2M<a/2 for every center cn. The bounded-Lipschitz distance is a supremum over all such tests for each data set, so it cannot tend to zero. This contradicts the linear pushforward of [F1] established in step 2.1 and proves the incompatibility.

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Projected empirical bridge CLT in the little-o multiscale space

Statement

Assume AC. Let P0 have a density f0 on [0,1] with ∥f0∥∞≤B<∞. Let (ψlk) be an orthonormal, compactly supported wavelet basis with 2l coefficients at level l≥1, uniformly bounded overlap, and ∥ψlk∥∞≤C02l/2. Suppose for some γ>1/2, max⁡k∣⟨f0,ψlk⟩∣≤Cf2−l(γ+1/2). Let wl≥1 be nondecreasing and admissible in Little-o multiscale coefficient space M0(w), and choose either cutoff regime 2Ln≍n1/(2γ+1)or2Ln≍(n/log⁡n)1/(2γ+1). For IID X1,…,Xn∼P0, define the finite wavelet projection Pn(Ln) by coefficients ⟨Pn(Ln),ψlk⟩=Pnψlk:=n−1∑i=1nψlk(Xi) for l≤Ln and zero for l>Ln, with the coarsest scaling coordinates projected as well. Let GP0 be a Borel centered Gaussian law on M0(w) whose coefficient covariance is Cov⁡(Glk,Gl′k′)=P0[(ψlk−P0ψlk)(ψl′k′−P0ψl′k′)]. Then n{Pn(Ln)−f0}⇒GP0in M0(w).

Facts & Assumptions

Given: AC, the density and wavelet bounds, the coefficient smoothness and cutoff conditions, IID observations, and the stated Borel Gaussian bridge law.

[F1]

Little-o multiscale coefficient space M0(w): M0(w) uses the norm sup⁡lwl−1max⁡k∣xlk∣, with normalized level maxima tending to zero.

[F2]

The multiscale coefficient space is separable and has vanishing projection tails: square-summable coefficient sequences lie in M0(w), and finite-level projections converge in its norm.

[F3]

Finite-projection convergence and posterior tail control imply weak BvM: convergence of every fixed finite projection together with vanishing tails under the approximating and limit laws implies bounded-Lipschitz convergence on M0(w).

[F4]

Multivariate iid central limit theorem: under AC, finite-second-moment IID vectors have the multivariate normal limit with their covariance, including singular covariance.

[F5]

The bounded-Lipschitz metric characterizes weak convergence on Polish spaces: on finite-dimensional Euclidean space, weak convergence of Borel probabilities implies convergence in bounded-Lipschitz distance.

[F6]

Finite and countable subadditivity of measures: a probability of a finite union is bounded by the sum of the component probabilities.

[F7]

Markov's inequality for random variables: for nonnegative Y and a>0, Pr⁡(Y≥a)≤E[Y]/a.

[F8]

Continuity from above when one set has finite measure: probabilities of decreasing measurable sets with finite first measure converge to the probability of their intersection.

[F9]

Identical distribution and IID families: IID means the observations are mutually independent and have a common law.

[A1]

The Axiom of Choice: AC is the stated axiom used by [F4] for finite-dimensional CLTs; no common null set over all directions is required because each projection level J is fixed.

[A2]

The basis satisfies the uniform support, overlap, coefficient-count and sup-norm bounds in the Statement.

[A3]

The truth coefficients satisfy the displayed Cf2−l(γ+1/2) bound.

Proof

Given: The probability law, basis, coefficient smoothness, admissible weights, cutoff, Gaussian limit law, and AC hypothesis in the Statement.

1.1F2givenalgebra

Pn(Ln) has finitely many nonzero coefficients, so it is in M0(w). The coefficient sequence of f0 is square-summable by Parseval, so [F2] places it in M0(w). Thus Un=n{Pn(Ln)−f0} is a well-defined M0(w)-valued random element.

1.2A1A2F4F5F9given

Fix J. For all sufficiently large n, Ln≥J, so the coordinates of PJUn are n−1/2∑i=1n(ψlk(Xi)−P0ψlk) for the finitely many indices through level J. The vector summand is bounded by [A2], has finite second moment, and is IID by [F9]; its covariance is the displayed covariance of GP0. By [F4] these finite-dimensional vectors converge weakly to the corresponding Gaussian projection. The projection space is finite-dimensional Euclidean with an equivalent weighted maximum norm, so [F5] gives convergence in bounded-Lipschitz distance for every fixed J.

1.3A2F7givenalgebra

Let Yi=ψlk(Xi)−P0ψlk. Then EYi=0, EYi2≤P0ψlk2≤B, and ∣Yi∣≤2C02l/2=:bl by [A2]. For m≥2, E∣Yi∣m≤blm−2EYi2. Since m!≥2 3m−2, expansion of the exponential gives, for 0<λbl<3n, Eexp⁡(λn−1/2∑i=1nYi)≤exp⁡(λ2B/[2(1−λbl/(3n))]). Applying [F7] to this exponential and optimizing at λ=t/(B+blt/(3n)) yields P0n{∣n(Pn−P0)ψlk∣>t}≤2exp⁡(−t2/[2(B+blt/(3n))]). Applying the same argument to −Yi supplies the lower-tail bound.

1.4A3F1givenalgebra

Above the cutoff, Un has only the deterministic bias coefficients −n⟨f0,ψlk⟩. By [A3] and monotonicity of wl, sup⁡l>Ln,kn∣⟨f0,ψlk⟩∣/wl≤Cfn 2−Ln(γ+1/2)/wLn. For the first cutoff regime the numerator is bounded, while wLn→∞. For the second, the numerator is O(log⁡n) and Ln≍log⁡n; admissibility wLn/Ln→∞ again makes the ratio vanish.

2.1F1F6step 1.3givenalgebra

Fix ε>0. By [F6] and step 1.3, P0n{max⁡J<l≤Ln,k∣n(Pn−P0)ψlk∣/wl>ε}≤∑J<l≤Ln2l+1exp⁡(−ε2wl2/[2(B+(2C0ε/3)2l/2wl/n)]). For levels with 2l/2wl/n≤1, the denominator is bounded by a constant depending only on B,C0,ε. Their sum is bounded by ∑l>J2l+1e−cεwl2, which tends to zero as J→∞: admissibility gives wl2/l→∞, so the summand is eventually bounded by 2−l.

3.1step 2.1givenalgebra

For the remaining levels 2l/2wl/n>1, the exponent in step 2.1 is at least cεwln/2l/2≥cεn/2Ln/2. Their total contribution is at most 2Ln+2exp⁡(−cεn/2Ln/2), which tends to zero. Indeed Ln=O(log⁡n) and either cutoff gives n/2Ln/2≥cnγ/(2γ+1) for all large n after decreasing c>0 if needed; this polynomial growth dominates Lnlog⁡2.

4.1step 2.1step 3.1algebra

The two threshold classes partition all levels J<l≤Ln. The low-threshold sum tends to zero as J→∞ by step 2.1, and the high-threshold sum tends to zero as n→∞ by step 3.1. Therefore the centered empirical-fluctuation tails vanish in the iterated limit n→∞, then J→∞.

5.1F2F8step 4.1step 1.4

For the fixed Gaussian law GP0, [F2] gives ∥GP0−PJGP0∥M(w)→0 pointwise. Hence the events {∥GP0−PJGP0∥M(w)>ε} decrease to the empty set; [F8] makes their probabilities tend to zero. Steps 4.1 and 1.4 give the matching posterior-tail condition for the laws of Un.

6.1F3step 1.2step 4.1step 1.4step 5.1∎

For each fixed J, step 1.2 gives convergence of the projected laws in bounded-Lipschitz distance; steps 4.1 and 1.4 give vanishing tails for Un, and step 5.1 gives vanishing tails for GP0. Applying [F3] to these laws proves βBL(L(Un),GP0)→0, which is the asserted weak convergence on M0(w).

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A bounded-density Gaussian bridge has a Borel multiscale law

Statement

Assume AC. Let P0 have density 0≤f0≤D<∞ on [0,1], and let (ψlk) be an orthonormal wavelet system with at most C2l coordinates per level, including finitely many coarsest scaling coordinates. The Haar system is allowed. For every admissible w, there exists a Borel centered Gaussian random element GP0 of M0(w) with coefficient covariance K((l,k),(l′,k′))=P0[(ψlk−P0ψlk)(ψl′k′−P0ψl′k′)]. Its Borel law is uniquely determined by these finite-coordinate Gaussian laws.

Facts & Assumptions

Given: AC, the bounded density, orthonormal system, finite level multiplicities, and admissible weights in the Statement.

[F1]

A mean and positive-semidefinite kernel define a Gaussian process constructs a Gaussian coordinate process for any symmetric positive-semidefinite kernel under AC.

[F2]

The multiscale coefficient space is separable and has vanishing projection tails: M0(w) is a separable Banach space; its coordinate projections PJ are contractions and converge pointwise in norm to the identity.

[F3]

Characteristic function of a normal law and Uniqueness of a law from its characteristic function: centered scalar normals have characteristic function e−vt2/2 and are determined by it under AC.

[F5]

Dominated convergence passes bounded almost-sure limits through expectation.

Proof

Given: The hypotheses in the Statement, including full AC.

1.1F1givenalgebra

The displayed kernel is symmetric and positive semidefinite because for any finite coefficients aj, ∑i,jaiajK(i,j)=P0[∑jaj(ψj−P0ψj)]2≥0. Thus [F1] constructs a centered jointly Gaussian coordinate sequence Z with this covariance. Each coordinate variance is at most P0ψlk2≤D.

2.1F3F4step 1.1algebra

For a centered normal of variance v≤D, completing the square in its normal density gives EetZ=evt2/2; at v=0 the variable is zero almost surely. Exponential Markov with t=u/D therefore gives Pr⁡(∣Z∣>u)≤2e−u2/(2D) when D>0, as it is for a probability density. Consequently Pr⁡{max⁡k∣Zlk∣>Rl+1}≤2C2le−R2(l+1)/(2D). Choose R with R2/(2D)>2log⁡2. The sum over l is finite, and the union bound over l≥J tends to zero. The probability that infinitely many of these events occur is therefore zero, since that event is contained in every such tail union.

3.1F2step 2.1constructalgebra

Almost surely the normalized maxima max⁡k∣Zlk∣/wl tend to zero, by step 2.1 and admissibility wl/l+1→∞; each of the finitely many remaining coordinates is finite. The event E={Z∈M0(w)} is coordinate-measurable, since the little-o condition is expressed by countable unions and intersections of the inequalities max⁡k∣Zlk∣/wl≤1/q. It has probability one. Define G=Z on E and G=0 otherwise. Its finite projections are measurable finite-dimensional random elements and converge everywhere in the separable Banach space [F2]. Hence G is Borel measurable: for every closed set F, the measurable functions d(PJG,F) converge to d(G,F); inverse images of closed sets are thus measurable, and closed sets generate the Borel sigma-algebra.

4.1F2F3F5step 3.1algebra

Let L be any continuous real linear functional on M0(w). Then L(PJG)→L(G) almost surely, and each approximant is centered normal with some variance vJ. These variances are bounded. Indeed, almost-sure convergence makes the laws tight: choose M so that Pr⁡{sup⁡J∣L(PJG)∣>M}<1/2, using that the supremum is finite almost surely. If vJ→∞ on a subsequence, the normal density bound would give Pr⁡(∣L(PJG)∣≤M)≤2M/2πvJ→0, a contradiction. Any convergent subsequence of (vJ) with limit v gives, by [F3] and [F5], EeitL(G)=e−vt2/2. Taking t=1 shows that all subsequential variance limits coincide. Thus vJ→v≥0, and [F3] identifies L(G) as N(0,v). Therefore G is a centered Borel Gaussian random element.

5.1F1F2step 3.1step 4.1algebra∎

Its coordinate covariance and finite Gaussian laws are unchanged by the null-set modification in step 3.1. Finally the Borel sigma-algebra of M0(w) equals the sigma-algebra generated by its countably many coordinates: the norm is their countable weighted supremum, so all open balls about a countable dense set are coordinate-measurable, and these balls generate the topology. Thus two Borel laws with the same finite-coordinate laws agree, by uniqueness of the cylinder law in [F1] restricted to this measurable space. This proves existence and uniqueness of the stated bridge law.

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Continuous and strictly increasing norm distributions for density bridges

Statement

Assume AC. Let P0 have density 0<ρ≤f0≤D<∞ on [0,1], and put F0(t)=∫0tf0. Use a complete real orthonormal wavelet basis, allowing the Haar basis with its finite scaling coordinate, and admissible weights w as in Little-o multiscale coefficient space M0(w). Assume the wavelet geometry and summability conditions of The multiscale primitive map is continuous into C[0,1], and write J:M0(w)→C([0,1]) for its primitive map. Let G be the Borel centered Gaussian bridge random element of A bounded-density Gaussian bridge has a Borel multiscale law, with coefficient covariance Cov⁡(Glk,Gl′k′)=P0[(ψlk−P0ψlk)(ψl′k′−P0ψl′k′)]. Then the distribution functions of ∥G∥M(w) and ∥JG∥∞ are continuous on R and strictly increasing on (0,∞). Both assign probability zero to 0, and take values strictly between 0 and 1 at every positive argument. Consequently, for every u∈(0,1), each has a unique positive finite lower u-quantile q, with CDF value u, and is strictly increasing on an open neighborhood of q.

Facts & Assumptions

Given: AC, the bounded positive density, complete wavelet basis, admissible weights, primitive map and Gaussian bridge in the Statement.

[F1]

The multiscale coefficient space is separable and has vanishing projection tails and The multiscale primitive map is continuous into C[0,1]: M0(w) is separable, finite-level projections converge in its norm, and J is continuous linear into C([0,1]).

[F2]

Logarithmic negative Sobolev spaces for white noise: the basis is complete and orthonormal in L2([0,1]), so its finite orthogonal projections converge in L2.

[F3]

A bounded-density Gaussian bridge has a Borel multiscale law supplies the Borel centered Gaussian law and its finite coefficient covariances. A finite stack of independent Gaussian vectors is jointly Gaussian and Mean and covariance determine Gaussian finite-dimensional laws identify finite Gaussian laws, including singular laws, by means and covariances under AC.

[F4]

For sigma-finite factors, the product measure exists, has the rectangle formula, is sigma-finite, and is unique supplies two independent copies of each Borel probability. Finite measures agreeing on a generating pi-system and on the whole space are equal identifies Borel laws from their finite-coordinate laws whenever those coordinates generate the Borel sigma-algebra.

[F5]

Finite and countable subadditivity of measures and Continuity from above when one set has finite measure give the countable null-union rule and continuity of probabilities along decreasing measurable events.

[F6]

Cauchy-Schwarz for random variables controls the difference of second moments when both factors converge in L2.

[F7]

Under AC, standard Brownian motion B exists by Existence of continuous Brownian motion, and put βt=Bt−tB1. The A-page definitions Brownian motion and Gaussian process, finite expectation linearity in Linearity, monotonicity, and the modulus bound for expectation, and Covariance is symmetric and bilinear in finite linear combinations give the direct bridge verification in step 4.2. Use the everywhere-continuous zero-start representative of Brownian reflection principle.

[F8]

Uncorrelated jointly Gaussian blocks are independent: finite jointly Gaussian blocks with zero cross-covariance are independent, including singular blocks.

[F9]

Brownian reflection principle: for a>0 and z≤a, P(max⁡t≤1Bt≥a,B1≤z)=P(B1≥2a−z).

[A1]

The Axiom of Choice: full AC is assumed for [F3], [F4], [F7]–[F9].

Proof

1.1A1F1F3F4givenconstruct

In either E=M0(w) or E=C([0,1]), the Borel sigma-algebra is generated by countably many continuous linear coordinates: the wavelet coordinates in the first case, and evaluations at rational times in the second. Indeed, the norm distance to a fixed point is their countable supremum, with the weights included in the first case; in the second case continuity makes the rational supremum equal the full supremum. Separability then gives a countable base of coordinate-measurable balls. Separability of M0(w) is [F1]; rational polygonal functions give a countable dense family in C([0,1]) by uniform continuity and finite rational approximation. Thus finite-coordinate laws determine Borel laws by [F4]. If X is any centered Borel Gaussian random element in either space and X′ an independent copy, [F3] gives −X=dX and X+X′=d2X: every finite coordinate vector on either side is centered Gaussian with the same covariance.

2.1F4F5step 1.1constructalgebra

For the law μ of such an X, let S be its support, the set of points whose every open neighborhood has positive probability. Its complement is the union of all zero-mass balls in a countable base, hence has measure zero by [F5]; S is closed and nonempty. Symmetry from step 1.1 gives S=−S. The support of X+X′ is S+S‾: independent positive-mass balls around s,t∈S give positive mass to every neighborhood of s+t, proving one inclusion; the other follows because X,X′∈S almost surely, so their sum lies almost surely in the closed set S+S‾. Scaling by 2 is a homeomorphism, so step 1.1 gives 2S=S+S‾. Taking any s∈S and −s∈S shows 0∈2S, hence 0∈S. Now x+0∈S+S‾=2S gives S⊆2S, while x+x∈2S gives 2x∈S and hence 2S⊆S. Therefore 2S=S and S+S‾=S. The set S is additive and symmetric, and division by 2 follows by applying division by 2 twice. It is closed under dyadic rational scalars, and closure gives all real scalars. Thus S is a closed linear subspace.

2.2A1F4F5F7F8F9step 1.1constructalgebra

Put Z=B1 and M=max⁡0≤t≤1βt. Every finite vector of bridge values is jointly Gaussian with Z and has zero cross-covariance, because Cov⁡(Bt−tB1,B1)=t−t=0. By [F8] these finite vectors are independent of Z. The coordinate generation in step 1.1 and finite-measure uniqueness [F4], applied to rectangles and then the generated sigma-algebra, show that the entire bridge path, and hence M, is independent of Z. Write ϕ for the standard-normal density. For c>ε>0, [F9] implies that the measure P(max⁡t≤1Bt<c,Z∈dz) on [−ε,ε] has density ϕ(z)−ϕ(2c−z): subtract the reflected-event measure from the terminal normal measure; the reflected-event CDF in [F9] differentiates to ϕ(2c−z) for z<c. Thus Aε(c):=P(max⁡t≤1Bt<c,∣Z∣≤ε)P(∣Z∣≤ε)=∫−εε[ϕ(z)−ϕ(2c−z)] dz∫−εεϕ(z) dz. For fixed a>0, take 0<ε<a/3. Since ∥B−β∥∞≤ε on {∣Z∣≤ε}, the inclusions with thresholds a−ε and a+ε, together with independence, give Aε(a−ε)≤P(M<a)≤Aε(a+ε). Continuity and positivity of ϕ show that both bounds tend to 1−ϕ(2a)/ϕ(0)=1−e−2a2. Hence P(M<a)=1−e−2a2 for every a>0. By [F5], P(M≤a)=lim⁡k→∞P(M<a+1/k)=1−e−2a2 for a>0, and M≥0 together with the same formula as a↓0 gives P(M=0)=0. Therefore M is atomless.

3.1F3step 2.1givenalgebra

If X has any nondegenerate scalar coordinate, then P(X=0)=0 and S≠{0}. For every r>0, 0∈S gives P(∥X∥<r)>0. A nonzero s∈S can be scaled to have norm greater than r, so some neighborhood of that scaled point lies in {∥X∥>r} and has positive probability. Likewise, for 0<a<b, scale s to have norm (a+b)/2; a sufficiently small ball about it is contained in {a<∥X∥<b} and has positive probability. Consequently its norm CDF is strictly between zero and one at every positive argument and strictly increasing there. This applies to G: any nonconstant wavelet has positive P0-variance, because f0≥ρ makes the P0 and Lebesgue null sets identical and a nonconstant wavelet cannot equal a constant almost everywhere.

4.1F3F5step 3.1givenalgebra

For each nonzero x∈M0(w), its norm is attained by some coordinate: if r=∥x∥M(w)>0, the normalized level maxima are below r/2 after finitely many levels, and the maximum over the remaining finite set equals r. Enumerate all coordinates by j, and write bj>0 for their norm weights: bj=wl on detail level l, and bj=1 for any additional Haar scaling coordinate. Hence, for r>0, {∥G∥M(w)=r} is contained in the countable union of events {∣Gj∣=rbj}. Each has probability zero: a positive-variance normal has a density, and a zero-variance centered normal is zero whereas rbj>0. By [F5] the union is null. At r=0, the nondegenerate coordinate from step 3.1 again gives probability zero; negative values are impossible. Absence of atoms and continuity of probability in [F5] show that this norm CDF is continuous on R.

4.2A1F1F2F3F6F7step 1.1step 3.1givenalgebra

First verify the bridge used in [F7] directly. Every finite linear combination of βtj=Btj−tjB1 is a finite linear combination of Brownian values with time 1 appended, so it is normal by [F7], including repeated times and singular combinations. Finite expectation linearity makes its mean zero. Covariance bilinearity gives Cov⁡(βs,βt)=min⁡(s,t)−ts−st+st=min⁡(s,t)−st for s,t∈[0,1]. On the single continuous zero-start Brownian path event supplied in [F7], subtraction of the continuous function tB1 makes β continuous, with β0=β1=0. Thus it is the needed centered continuous Gaussian bridge, without an example as a logical supplier. Write Y=JG. For every continuous real linear functional L on C([0,1]), L∘J is continuous linear on M0(w), so L(Y) is centered normal by [F3]; thus Y is centered Gaussian. For s∈[0,1], let pN1[0,s] be the orthogonal wavelet projection through level N. Its Lebesgue L2 limit is 1[0,s] by [F2], and f0≤D gives the same convergence in L2(P0). Put UN(s)=J(PNG)(s). The coefficient covariance in [F3] gives Cov⁡(UN(s),UM(t))=P0[(pN1[0,s]−P0pN1[0,s])(pM1[0,t]−P0pM1[0,t])]. In particular UN(s) is Cauchy in L2, and it converges almost surely to Y(s) by [F1]. Its L2 limit therefore equals Y(s) almost surely, since convergence in L2 implies convergence in probability and two probability limits agree. The means are zero; applying [F6] to the product differences passes the covariances to the limit. Thus Y is a centered continuous Gaussian process with covariance F0(s∧t)−F0(s)F0(t). The function F0 is a continuous strictly increasing bijection of [0,1] onto itself. By [F3], Y and t↦βF0(t) from [F7] have the same finite Gaussian laws; step 1.1 then gives equality of their Borel laws on C([0,1]). In particular ∥Y∥∞=d∥β∥∞, and Y has a nondegenerate evaluation coordinate, for example at any s with 0<F0(s)<1. Step 3.1 therefore applies to its norm as well.

5.1F3F5step 4.2step 2.2algebra

By symmetry of the centered Gaussian bridge, −min⁡tβt has the same atomless distribution as M. For r≥0, continuity on a compact interval gives {∥β∥∞=r}⊆{M=r}∪{−min⁡tβt=r}. Both events on the right are null by step 2.2 and symmetry; [F5] gives no atom at r. Negative norm values are impossible. By step 4.2, the CDF of ∥JG∥∞ is therefore continuous on R.

6.1F1F5step 3.1step 4.1step 4.2step 5.1givenalgebra∎

Both norm CDFs are continuous by steps 4.1 and 5.1, vanish at zero, and are strictly increasing on (0,∞) with values strictly between zero and one by steps 3.1 and 4.2. They tend to one at infinity because both random norms are finite almost surely. For each u∈(0,1), continuity therefore gives a positive finite point q with CDF value u, strict increase gives its uniqueness, and monotonicity makes it the lower u-quantile. Any sufficiently small open interval around q is contained in (0,∞), where strict increase holds. These are all the asserted quantile conditions.

LemmaStatement: Literature-sourcedProof: AI-adaptedOpen item page →

Finite Dirichlet gamma representation and weighted Bernstein bound

Statement

Assume AC. Let β1,…,βm>0, B=∑jβj, and let Zj be independent Gamma⁡(βj,1) variables. Put S=∑jZj. Then ω=(Zj/S)j is Dirichlet⁡(β1,…,βm), and S is Gamma⁡(B,1), with mean B and variance B. Each Zj has mean βj, variance βj, and moment-generating function EeuZj=(1−u)−βj for every real u<1. For real qj satisfying ∣qj∣≤b, put T(q)=∑jqj(Zj−βj) and V=∑jβjqj2. If V>0, then for x>0, Pr⁡{∣T(q)∣>x}≤2exp⁡{−x22(V+bx)}. If V=0, T(q)=0 almost surely. Sums of disjoint groups of the Zj are independent Gamma variables with their respective summed shapes.

Facts & Assumptions

Given: Full AC, the positive finite shape vector, and the weights in the Statement.

[F1]

Shape-rate Gamma distribution and The shape-rate Gamma density is normalized supply the normalized density za−1e−z/Γ(a), z>0, for a>0.

[F2]

Dirichlet distribution, including the one-category case specifies the normalized density Γ(B)∏jωjβj−1/∏jΓ(βj) on the simplex, and the point mass at one for m=1.

[F4]

Markov's inequality for random variables: for a nonnegative random variable Y and a>0, Pr⁡(Y≥a)≤EY/a. Applied to Y=eλT(q) with λ>0 and a=eλx, it gives Pr⁡(T(q)≥x)≤e−λxEeλT(q).

[F5]

Uniqueness of a multivariate exponential transform identifies laws having the same finite moment-generating transform near zero under AC.

Proof

Given: The hypotheses in the Statement.

1.1F1F2F3givenalgebracases

The product Gamma law exists by [F3]. In its density make the substitution zj=sωj, ωm=1−∑j<mωj. Its Jacobian is sm−1: factor s from the proportion columns of the derivative matrix and add its first m−1 rows to the last; the remaining last row has first entry one and all other entries zero. The resulting density factors as sB−1e−s/Γ(B) times the simplex density in [F2]. Integrating either normalized factor proves both distributional assertions. For m=1, ω1=1 directly.

2.1F1F3F5step 1.1algebra

Substituting y=(1−u)z in the Euler Gamma density gives EeuZj=(1−u)−βj for u<1. Its first two derivatives at zero yield mean βj and variance βj; differentiation is justified by an exponential majorant with any fixed parameter in (0,1). Independence makes the joint transform of disjoint group sums the product ∏h(1−uh)−∑j∈Ihβj, which is the transform of the corresponding product Gamma law. By [F5], these are the same laws. In particular S has the asserted mean and variance, also following from step 1.1.

3.1F4step 2.1algebracases∎

For ∣λ∣b<1, independence and step 2.1 give log⁡EeλT(q)=∑jβj[−log⁡(1−λqj)−λqj]≤λ2V/[2(1−∣λ∣b)]. Indeed the convergent logarithm series gives −log⁡(1−u)−u≤∑r≥2∣u∣r/r≤u2/[2(1−∣u∣)] for ∣u∣<1. If V>0, set λ=x/(V+bx); exponential Markov then bounds the upper tail by exp⁡[−x2/(2(V+bx))]. Apply the same calculation to −q and sum the bounds. If V=0, positivity of all βj forces every qj=0, so T(q)=0.

TheoremStatement: Literature-sourcedProof: AI-adaptedOpen item page →

Type-H histogram posterior weak Bernstein–von Mises theorem

Statement

Assume AC. Use the type-H prior of Type-S log-density and type-H histogram prior families, retaining its original conditions: 1/2<α≤1, f0∈Cα([0,1]), 0<ρ0≤f0≤D0<∞, either original cutoff Ln=jn or Ln=ℓn, and c12−Lna≤ak,Ln≤c2 for fixed positive a,c1,c2. Write mn=2Ln. In the Haar convention, the scaling function is 1, the detail functions are ψlk=2l/2(1Il+1,2k−1Il+1,2k+1),l≥0,0≤k<2l, and a histogram at resolution Ln has only the scaling coordinate and levels l<Ln. Let X1,…,Xn be IID from f0, let Nnk=∑i1ILn,k(Xi), and define the empirical histogram hn(x)=mnNnk/non ILn,k. Let Πn(⋅∣Xn) be the density posterior for the stated histogram prior. For every nondecreasing wl≥1 with wl/l+1→∞, its conditional law Qn of n(f−hn) satisfies βBL,M0(w)(Qn,L(GP0))⟶0 in P0n-probability, where the Borel centered Gaussian bridge GP0 is supplied by A bounded-density Gaussian bridge has a Borel multiscale law and has covariance P0[(ψ−P0ψ)(ψ′−P0ψ′)]. Its scaling coordinate is zero. This proves the type-H source-specific posterior BvM with the empirical projection center; no additional contraction, bias, or Dirichlet-parameter condition is imposed.

Facts & Assumptions

Given: AC, the original type-H truth, cutoff, parameter, Haar, observation, and admissible-weight conditions in the Statement.

[F1]

Finite Dirichlet gamma representation and weighted Bernstein bound: a Dirichlet vector of shapes βk is Zk/S for independent Gamma(βk,1) variables; S has mean and variance B=∑kβk. For T(q)=∑kqk(Zk−βk), ∣qk∣≤b, and V=∑kβkqk2>0, Pr⁡(∣T(q)∣>x)≤2e−x2/[2(V+bx)]. Disjoint Gamma shapes add, and EeuZk=(1−u)−βk for u<1.

[F2]

Dirichlet-Multinomial conjugate update and Bayes formula for dominated kernels identify the positive finite normalized Dirichlet likelihood update.

[F3]

A bounded-density Gaussian bridge has a Borel multiscale law supplies the Borel Gaussian bridge law for the bounded density in the Statement.

[F4]

Finite-projection convergence and posterior tail control imply weak BvM concludes BL convergence from every fixed finite-coordinate BL limit and vanishing posterior tails in the iterated limit.

[F5]

Prokhorov tightness theorem on polish spaces gives subsequential weak compactness of tight finite-dimensional Borel laws under AC; Uniqueness of a multivariate exponential transform identifies finite laws with a common moment-generating transform near zero.

[F6]

Vector Slutsky theorem passes a finite-dimensional weak limit through algebraic operations with quantities converging in probability to constants. The bounded-Lipschitz metric characterizes weak convergence on Polish spaces converts finite-dimensional weak convergence to BL convergence.

[F8]

Finite type-S and type-H prior draws are L2 probability densities supplies the finite histogram density construction. Little-o multiscale coefficient space M0(w) supplies the coefficient norm and admissibility convention, with the finite scaling coordinate included.

Proof

Given: All hypotheses in the Statement, with full AC throughout.

1.1F1F2givenalgebra

Abbreviate m=mn, ak=ak,Ln, A=∑kak, βk=Nnk+ak, and B=n+A. The original cutoff conditions and α>1/2 give m/n→0 and mlog⁡n/n→0, and A≤c2m. On the positive simplex, the full-data histogram likelihood is mn∏kωkNnk. Multiplication by the prior density yields a constant times ∏kωkβk−1, with every shape positive; its normalization is finite positive by [F2]. Therefore the full-data posterior is Dirichlet(βk)k, regardless of whether the actual sampling truth is itself a histogram. By [F1] realize it by ωk=Zk/S. Write Rn for the posterior mean histogram measure, identified with its density in coefficient differences, with cell masses βk/B. For a cell-constant function q, set T(q)=∑kqk(Zk−βk). Direct subtraction gives n(ωq−Rnq)=(n/S)T(q−Rnq).

2.1F7step 1.1algebra

Fix constants t>0 and C large enough that c:=tC−D0(et−1)>0. Since Nnk is Binomial(n,pk) with pk=P0ILn,k≤D0/m, independence of the observations gives EetNnk=(1+pk(et−1))n≤enD0(et−1)/m. Hence En={max⁡kNnk≤Cn/m} satisfies P0n(Enc)≤me−cn/m→0, by exponential Markov and the union bound. On En, for all sufficiently large n, βk≤C′n/m, B≤2n, and both the empirical histogram density and the mean histogram density are bounded by a fixed constant C′ independent of n.

2.2F1F7step 1.1givenalgebra

Fix finitely many Haar coordinates. Choose a fixed coarse dyadic partition of r cells on which all their functions are constant. For large n its cells are unions of level-Ln cells. By [F1], the corresponding grouped Gamma variables Znj are independent Gamma(bnj,1) with bnj=Nn(Jj)+∑ILn,k⊂Jjak. Their summed shape is still B. Write pj=P0(Jj)>0. Each coarse count satisfies E[Nn(Jj)/n]=pj and variance at most 1/(4n), by observation independence. Markov applied to squared deviations, together with A/n→0, proves bnj/n→pj in P0n-probability simultaneously for the fixed finite partition.

3.1F1F7step 1.1step 2.1algebracases

On En, take any Haar detail ψ=ψlk with l<Ln and put q=ψ−Rnψ. Then ∣q∣≤2 2l/2 and V=∑kβkqk2=BVar⁡Rn(ψ)≤BRnψ2≤C′n, using ∫ψ2=1 and the density bound. By [F1] and [F7], Pr⁡(S<B/2∣Xn)≤4/B, because Var⁡(S)=B. On the complement, step 1.1 yields ∣n(ωψ−Rnψ)∣≤2∣T(q)∣/n. Thus, apart from the single event {S<B/2}, the conditional probability that this absolute coefficient exceeds x is at most 2exp⁡{−c0x2/(1+2l/2x/n)} for a fixed c0>0. The zero-variance case has no such failure event, by [F1].

3.2F1F5F7step 2.2algebra

Consider any deterministic data sequence along which bnj/n→pj for every j. Under its conditional Gamma product laws put Ynj=(Znj−bnj)/n. For every fixed t∈Rr, [F1] and the logarithm series give log⁡Eet⋅Yn=∑jbnj[−log⁡(1−tj/n)−tj/n]→12∑jpjtj2. The remainder is O(n−3/2∑jbnj∣tj∣3)=O(n−1/2). The means of Yn are zero and their total second moments are B/n=O(1), so their laws are tight by the squared-norm Markov bound and compactness of finite-dimensional closed balls. By [F5], any subsequence has a further weak limit. For any fixed t, the same expansion at 2t uniformly bounds Ee2t⋅Yn; hence et⋅Yn is uniformly integrable. Truncation of this continuous exponential therefore passes its expectation through each weakly convergent subsequence. The limit law has transform exp⁡(12∑jpjtj2) and an exponential moment on a neighborhood of zero: eδ∑j∣yj∣≤∑ϵ∈{−1,1}reδϵ⋅y and the corresponding transforms are finite. The independent centered normal vector with variances pj has this same transform, by completing the square in each normal density. Transform uniqueness [F5] identifies every subsequential limit, proving Yn⇒Nr(0,diag⁡(p)).

4.1F4F7F8step 2.1step 3.1algebra

Choose a fixed K>0 sufficiently large. Uniformly over l<Ln, 2l/2Kl+1/n≤Km(Ln+1)/n→0. Summing the exponential bounds of step 3.1 over levels J<l<Ln and their 2l coefficients therefore gives, for all large n, Πn{max⁡J<l<Ln,k∣n(f−Rn)lk∣/l+1>K∣Xn}≤4/B+∑l>J2l+1e−c1K2(l+1) on En, with fixed c1>0. The probability 4/B is counted only once, since the same S normalizes every coordinate. Choose K with c1K2>2log⁡2; the displayed series tail then tends to zero with J. For any ε>0, admissibility gives Kl+1≤εwl for all sufficiently large l. Both f and Rn are histograms, so all their detail coordinates at l≥Ln vanish. Consequently their conditional M(w) tails vanish in the iterated limit of [F4], first n→∞, then J→∞, since P0n(Enc)→0.

5.1F8step 1.1step 2.1step 4.1algebra

For a Haar detail ψ=ψlk, exact subtraction gives n(Rnψ−Pnψ)=n[∑kakψk−APnψ]/B. Haar cell values satisfy m−1∑k∣ψk∣=∫∣ψ∣=2−l/2≤1. Hence ∣∑kakψk∣≤c2m, while on En, ∣Pnψ∣≤C∫∣ψ∣≤C. This bounds every such mean shift by C′′m/n→0. The scaling-coordinate shift is exactly zero, and all coordinates at l≥Ln vanish for both centers. Since wl≥1, ∥n(Rn−hn)∥M(w)→0 uniformly on En. In particular step 4.1 also supplies the required posterior tails about hn.

6.1F3F6step 5.1step 3.2algebra

Here (S−B)/n=∑jYnj, S/n→1 in conditional probability by its variance B/n2→0 and mean B/n→1. Exact algebra gives n(Znj/S−bnj/B)=(n/S)[Ynj−(bnj/B)∑hYnh]. By [F6] and step 3.2, this vector converges to (Uj−pj∑hUh)j, with Uj independent N(0,pj). Its covariance is diag⁡(p)−ppT. Applying the fixed linear map from coarse-cell masses to the chosen Haar coordinates yields covariance exactly P0[(ψ−P0ψ)(ψ′−P0ψ′)]. Step 5.1 removes the mean shift from Rn to hn on En. Thus along every deterministic data sequence with the ratios in step 2.2 converging and En eventually occurring, the finite-coordinate posterior converges weakly, hence in BL by [F6], to the corresponding projection of [F3].

7.1F6step 2.1step 2.2step 6.1givenchoosecontradiction

The preceding deterministic-sequence conclusion implies the finite-coordinate BL convergence in P0n-probability. To see this without a simultaneous conditional null-set assertion, if that convergence failed, there would be ε,η>0 and infinitely many n with probability at least η that the distance exceeds ε. Along a subsequence, step 2.2 and P0n(Enc)→0 make the probability of a ratio error above 1/q or Enc smaller than η/2 at its qth chosen index. Thus at each such index there exists data with distance above ε, ratio error below 1/q, and En true. AC selects a deterministic sequence of those data, contradicting step 6.1. This proves the asserted convergence in probability for each fixed finite projection.

8.1F3F4F8step 4.1step 5.1step 7.1algebra∎

The posterior histogram construction [F8] and its finite-dimensional simplex kernel make Qn a data-indexed Borel probability on M0(w): each draw and hn has only finitely many Haar coefficients, and its map from simplex coordinates is continuous. The target is the Borel bridge law [F3]. Step 7.1 supplies every fixed finite-projection BL limit, and steps 4.1, 5.1 supply its posterior-tail condition. Apply [F4] to obtain the stated M0(w) BL convergence. Every original type-H assumption has been retained; in particular the lower parameter bound is compatible with, but is not needed beyond, positivity in this conjugate proof.

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Compact wavelet projections approximate smooth functions and commute asymptotically with multiplication

Statement

Let VL be the span of wavelets through level L in a compactly supported orthonormal multiresolution basis on [0,1], either boundary corrected or periodized. Assume constants belong to VL, its dimension dL≍2L, and its orthonormal scaling functions ϕLk have supremum norm at most C2L/2, support diameter at most C2−L, and uniformly bounded overlap. Periodized supports and distances are interpreted on the circle. Assume also ∑k∣ψlk(x)∣≤C2l/2 and ∥ψlk∥1≤C2−l/2. Let PL denote the orthogonal projection onto VL.

Then PL has a kernel KL satisfying sup⁡x∫∣KL(x,y)∣dy≤C′ and KL(x,y)=0 when dist⁡(x,y)>C′2−L. If a is β-Hölder for 0<β≤1, then ∥PL(ah)−ah∥∞≤C′∥a∥Cβ2−βL∥h∥∞,h∈VL. For the composition assertion, assume additionally an integer m>α such that ∥ψlk(q)∥∞≤Cq2l(q+1/2) for 0≤q≤m, bounded overlap also for their derivatives, and vanishing moments through degree m−1 for the detail wavelets, including boundary wavelets; the finite low scaling functions are Cm. These are the usual sufficiently regular compact wavelet hypotheses. If a bounded function g has coefficients bounded by Cg2−l(α+1/2), with α>0, and its wavelet expansion represents g in L2, then ∥g−PLg∥∞≤C′′Cg2−αL, up to equality of the continuous representatives. Under these additional derivative and cancellation hypotheses, eg also has coefficients bounded by Cg′2−l(α+1/2), including integer α, and g,eg are β-Hölder for every 0<β<min⁡(α,1). Moreover ∥h∥∞≤C′′dL∥h∥2 for h∈VL.

Facts & Assumptions

Given: The explicitly stated compact multiresolution, scaling-function, wavelet, and Hölder assumptions.

[F1]

Logarithmic negative Sobolev spaces for white noise supplies the orthonormal coefficient convention; all additional localization hypotheses are stated above.

Proof

1.1F1givenalgebra

The finite orthogonal projection has kernel KL(x,y)=∑kϕLk(x)ϕLk(y). At each x only a uniformly bounded number of terms are nonzero, and each has ∥ϕLk∥1≤C2−L/2. Thus ∫∣KL(x,y)∣dy≤∑k:ϕLk(x)≠0∣ϕLk(x)∣∥ϕLk∥1≤C′. A nonzero term requires x,y to lie in one scaling support, giving the support bound. Also KL(x,x)=∑kϕLk(x)2≤C′2L; Cauchy–Schwarz on the scaling coefficients gives the claimed L2 to L∞ bound.

1.2F1givenalgebra

The levelwise tail satisfies ∥∑k⟨g,ψlk⟩ψlk∥∞≤CCg2−αl. Summing its geometric series over l>L proves uniform convergence and the claimed approximation rate. Its uniform limit agrees with its L2 limit, hence with g almost everywhere, and everywhere for continuous representatives.

2.1givenstep 1.1algebra

For h∈VL, PLh=h. Therefore PL(ah)(x)−a(x)h(x)=∫KL(x,y)(a(y)−a(x))h(y)dy. Hölder continuity, the support bound, and the kernel integral bound give the asserted commutator estimate.

2.2givenstep 1.2algebra

For composition put uj=Pjg and vj=uj−uj−1, with the first finite low block treated as u0. Levelwise derivative bounds and overlap give ∥vj(q)∥∞≤Cg2j(q−α) for 0≤q≤m, and ∥uj(q)∥∞≤Cg′2jq for 1≤q≤m by summing levels; also sup⁡j∥uj∥∞<∞. The identity euj−euj−1=vj∫01euj−1+tvjdt and repeated product and chain rules therefore give, writing Hj=euj−euj−1, ∥Hj∥∞≤C2−jα and ∥Hj(m)∥∞≤C2j(m−α). Indeed a derivative of order q of the exponential factor is a finite sum of products of derivatives of its exponent of total order q, bounded by C2jq; pairing with the derivative of order m−q of vj gives C2j(m−α).

3.1givenstep 2.2algebra

The telescoping series eg=eu0+∑j≥1Hj converges uniformly. For a wavelet at level l, the terms with j≥l have coefficients bounded by C2−l/2∑j≥l2−jα≤C2−l(α+1/2). For j<l, subtract the degree m−1 Taylor polynomial of Hj about a point of the wavelet support; all its integrals vanish by the stated moments. The Taylor remainder gives ∣⟨Hj,ψlk⟩∣≤C2−l(m+1/2)2j(m−α). Sum the geometric series over j<l to get the same C2−l(α+1/2) bound. The fixed smooth eu0 has the stronger order 2−l(m+1/2). This proves composition in the coefficient class directly, for every positive α including integers, without presuming a Hölder–wavelet equivalence.

4.1givenstep 1.2step 2.2algebra∎

For 0<β<min⁡(α,1) the levelwise derivative and supremum bounds for g are respectively at most C2j(1−β) and C2−jβ. Given distance 0<δ<1, choose J with 2−J−1<δ≤2−J. The difference of the levels through J is at most Cδ∑j≤J2j(1−β)≤Cδβ by the derivative bound; the remaining difference is at most C∑j>J2−jβ≤Cδβ. Thus g is β-Hölder. The exponential has bounded derivative on the bounded range of g, so eg has the same Hölder bound.

LemmaStatement: AI-adaptedProof: AI-adaptedOpen item page →

Type-S posterior contracts in quotient log-density coordinates without a tail restriction on a log-Lipschitz prior

Statement

Assume AC for the imported measure and Gaussian interfaces. Use Type-S priors and either cutoff of Type-S log-density and type-H histogram prior families with the compact multiresolution basis of Compact wavelet projections approximate smooth functions and commute asymptotically with multiplication, regular enough for the truth's Hölder approximation. Suppose 0<ρ0≤f0≤D0, g0=log⁡f0∈Cα, and α>1/2. In S1 take σl=2−l(α+1/2) and any probability density whose logarithm is Lipschitz on all of R. In S2 take Gaussian coefficients with σl=2−l(r+1/2) and 0<r<α−1/4.

Write d=dim⁡VLn≍2Ln, ELn=VLn∩{h:∫h=0}, θ=T−∫T, θ∗=PLng0−∫g0, and en=d/n+d−α. Under IID data of density f0, the posterior distributions of ∥θ−θ∗∥2/en are tight in probability. Equivalently, for every deterministic bn→∞, Π(∥θ−θ∗∥2>bnen∣Xn)→0 in P0n-probability. The normalizer defining the posterior is positive and finite P0n-almost surely. The quotient prior has a positive continuous Lebesgue density qL on EL. In S1 it obeys ∣log⁡qL(θ+u)−log⁡qL(θ)∣≤BL∥u∥2,BL2≤C∑l≤L2lσl−2, and a shift in a single high wavelet coordinate obeys the sharper bound C∣ulk∣/σl. The low scaling block has a fixed finite collection of analogous weighted bounds. In S2 the quotient prior is centered Gaussian, with precision QL diagonal on high wavelets with entries σl−2 and a fixed positive definite low scaling block. Its log-density increment is −⟨QLθ,u⟩−⟨QLu,u⟩/2.

Facts & Assumptions

Given: AC and the density, basis, cutoff, coefficient, and regularity hypotheses of the Statement.

[F1]

Compact wavelet projections approximate smooth functions and commute asymptotically with multiplication gives ∥PLg0−g0∥∞≤Cd−α and ∥u∥∞≤Cd∥u∥2 on VL.

[F2]

Tonelli's theorem for nonnegative measurable functions on a sigma-finite product permits integration of nonnegative likelihoods in either order.

[F3]

Markov's inequality for random variables bounds a nonnegative variable's upper tail by its expectation divided by the threshold.

Proof

1.1givenF2algebra

Quotient out constants before using likelihood curvature. Constants belong to the fixed low scaling space. An orthogonal change within that finite space separates T=θ+c1; integrate c out of the prior and write qL for the resulting Lebesgue density on EL. The likelihood depends only on θ. In S1 its product density before integration obeys p(θ+u,c)/p(θ,c)∈[e−BL∥u∥2,eBL∥u∥2], where BL2≤C∑l≤L2lσl−2≤Cd2α+2. Integrating preserves both inequalities for qL; it is positive, finite almost everywhere, and the log-Lipschitz inequality supplies its positive continuous finite version everywhere. In S2 the marginal is a nondegenerate Gaussian on EL, with precision QL equal to σl−2 on high wavelets and a fixed positive definite low block; hence ∥QL∥≤Cd2r+1.

1.2F1F3givenalgebra

Let f∗=eθ∗/∫eθ∗. [F1] gives ∥f∗−f0∥∞≤Cd−α. For ℓ(θ)=n(Pnθ−log⁡∫eθ), the centered score at θ∗ has expected squared Euclidean norm at most Cnd: sum the coordinate variances, each bounded by D0 by orthonormality. The score's deterministic mean is the coefficient vector of n(f0−f∗), with norm at most Cnd−α. Consequently [F3] gives ∥∇ℓ(θ∗)∥2=OP(nen). On every ball ∥u∥2≤Ren with fixed R, [F1] and den→0 make fθ∗+u bounded uniformly above and away from zero. For v∈EL, Var⁡f(v)=inf⁡a∫(v−a)2f lies between c∥v∥22 and C∥v∥22, using ∫v=0. Thus −∇2ℓ is between cnI and CnI on these balls. Convexity of −ℓ holds globally.

2.1givenstep 1.1algebra

In S1, BL≤Cnen by either cutoff. In S2 the Hölder coefficient bound gives GL2:=∥QLθ∗∥22≤C[1+∑l≤L2l(4r+2−2α)], so GL≤Cnen, and ∥QL∥/n→0 because r<α. The Gaussian log-density increment is exactly −⟨QLθ∗,u⟩−⟨QLu,u⟩/2. In particular its radial upper slope is at most GL, and on the en ball it is bounded below by −GLen−∥QL∥en2/2.

3.1step 1.1step 1.2step 2.1algebra

Fix a score event ∥∇ℓ(θ∗)∥2≤Anen. Put r0=Ren, with R a large fixed constant. Taylor's formula on the r0 ball bounds ℓ(θ∗+r0ω)−ℓ(θ∗) above by Anenr0−cnr02/2 and its radial derivative above by Anen−cnr0. Global convexity of −ℓ extends this derivative bound to every r≥r0. Add the prior bound BLr in S1, or GLr with its nonpositive quadratic term in S2. For R large enough the log unnormalized posterior ratio H(rω) relative to θ∗ is at most −c′nr0r for all r≥r0. On r≤en, the lower Taylor bound and the prior lower bounds instead give H≥−CAnen2.

4.1F3step 1.2step 3.1algebra

Polar integration in dimension m=d−1 bounds the tail/normalizer ratio by eCAnen2m∫R∞tm−1e−c′nRen2tdt. Here nen2≥d>m. Choose R so large that log⁡t≤c′Rt/4 for t≥R and CA≤c′R2/4. The integral is then at most [m/(c′′nRen2)]e−c′′nR2en2 after decreasing c′′>0, and tends to zero. The denominator used here is the integral on the en ball, at least its volume times e−CAnen2 times the positive unnormalized value at θ∗. First increase A to make its score event arbitrarily probable, then increase R. This proves tightness. For any bn→∞, eventual containment of every fixed Ren ball in the bnen ball yields the stated equivalent formulation.

5.1F2givenalgebra∎

Every modeled density is everywhere positive. Its prior predictive product density is positive and integrates to one by [F2], so it is finite Lebesgue-almost everywhere on the sample cube. The law P0n has a bounded Lebesgue density, hence the same exceptional set is P0n-null. This proves finite positive evidence on the asserted fibers independently of the score event.

TheoremStatement: AI-adaptedProof: AI-adaptedOpen item page →

Type-S density posteriors satisfy the weak multiscale Bernstein–von Mises theorem

Statement

Assume AC. Let X1,…,Xn be IID on [0,1] with density 0<ρ0≤f0≤D0<∞, and suppose g0=log⁡f0∈Cα. Use a sufficiently regular compactly supported boundary corrected orthonormal multiresolution wavelet basis satisfying Compact wavelet projections approximate smooth functions and commute asymptotically with multiplication, with regularity greater than α, and let VL contain exactly its wavelet levels through L, including the fixed low scaling space and constants. Its regularity and vanishing moments satisfy the composition hypotheses in that lemma for some integer m>α. Let Ln be either of the two cutoff sequences in Type-S log-density and type-H histogram prior families, fixed consistently for all n.

In Type-S1 take α>1, σl=2−l(α+1/2), and any coefficient probability density with globally Lipschitz logarithm. In Type-S2 take α>1/2, Gaussian coefficients, and σl=2−l(r+1/2) with 0<r<α−1/4. Normalize f=exp⁡(T)/∫exp⁡(T) as in that definition. For every admissible weight sequence w, the posterior satisfies βBL,M0(w)(L(n(f−Pn(Ln))∣Xn),L(GP0))⟶0 in P0n-probability, where Pn(Ln) has empirical wavelet coefficients through Ln and zero coefficients above Ln, and GP0 is the Borel Gaussian bridge with covariance P0[(ψi−P0ψi)(ψj−P0ψj)].

Facts & Assumptions

Given: The model, truth, multiresolution basis, prior scales, cutoff, admissible weights, and full AC in the Statement. Put d=dim⁡VLn≍2Ln, en=d/n+d−α, and λl=max⁡(l,1) to include the fixed low levels.

[F1]

Type-S posterior contracts in quotient log-density coordinates without a tail restriction on a log-Lipschitz prior gives quotient-coordinate contraction at radius en around θ∗=PLng0−∫g0; its Statement supplies the positive quotient marginal prior density and its shift bounds.

[F2]

Compact wavelet projections approximate smooth functions and commute asymptotically with multiplication gives the uniform projection kernel bound, approximation, L2 to supremum bound, and the multiplication commutator estimate. Its composition conclusion proves that f0=eg0 has the required α coefficient decay, including integer α, and that f0 is β-Hölder for every 0<β<min⁡(α,1).

[F3]

A bounded-density Gaussian bridge has a Borel multiscale law constructs the Gaussian bridge law on M0(w) under AC.

[F4]

Finite-projection convergence and posterior tail control imply weak BvM reduces the asserted bounded-Lipschitz convergence to fixed finite projections and vanishing posterior tails.

[F5]

Bernstein tail bound for independent bounded sums gives Bernstein's inequality for independent centered bounded variables.

[F6]

Prokhorov tightness theorem on polish spaces, Uniqueness of a law from its characteristic function, and Cramer wold device give subsequential weak compactness from tightness, uniqueness from characteristic functions, and joint convergence from scalar projections under AC.

[F7]

The bounded-Lipschitz metric characterizes weak convergence on Polish spaces metrizes finite-dimensional weak convergence; Dominated convergence permits integrable domination; Markov's inequality for random variables gives Markov's bound.

Proof

1.1F1F2givenchoose

Choose a deterministic bn→∞ sufficiently slowly that bnden→0 and bnend2r+1/n→0 in the Gaussian case. Such a choice exists: the first unmultiplied expression tends to zero because α>1/2, and the second is bounded by a logarithmic factor times d2r−2α+1/2→0. Set Dn={∥θ−θ∗∥2≤bnen} in the quotient by constants used in [F1]. Then Π(Dn∣Xn)→1 in probability. On Dn, ∥θ−θ∗∥∞≤Cbnden=o(1); hence ∥f−f0∥∞=o(1) uniformly, and the densities are bounded above and away from zero. Write ΠD for the posterior conditioned on Dn.

2.1givenstep 1.1algebra

For γ=ψlk, l≤Ln, define fs=fe−sγ/n/Pfe−sγ/n. For ∣s∣≤λl, Taylor expansion of the log moment generating function gives sn(Pf−Pn)γ=ℓn(fs)−ℓn(f)+(s2/2)Var⁡fγ+R, where ∣R∣≤C∣s∣3∥γ∥∞/n. To justify the uniform remainder, differentiate a↦log⁡Pfeaγ three times; its third derivative is the third centered moment under the tilted density, bounded by C∥γ∥∞Pfγ2 when ∣a∣∥γ∥∞=o(1). On Dn, Pfγ2≤C by orthonormality and the density bound, while Ln2Ln/2/n→0. Thus ∣R∣≤Cs2 and Var⁡fγ≤C. Here ℓn is the sum log likelihood.

3.1F1step 1.1step 2.1algebra

The map f↦fs is the quotient-coordinate translation θ↦θ−s(γ−∫γ)/n. On high wavelets it shifts one coordinate; low scaling directions involve only a fixed finite-dimensional block. In S1 the absolute log prior density ratio is at most C∣s∣/(nσl)≤C∣s∣, since 2Ln(α+1/2)≤n. In S2 it is at most C[∣s∣(∣g0,lk∣+bnen)/(nσl2)+s2/(nσl2)], with a bounded fixed low-block version. Uniformly in high l≤Ln, its coefficients are bounded: ∣g0,lk∣≤C2−l(α+1/2), bnend2r+1/n=o(1), and d2r+1/n=o(1). Changing variables in the numerator likelihood integral and discarding its transformed Dn indicator therefore bounds that integral by eC∣s∣+Cs2 times the full posterior normalizer. Step 2.1 yields EΠDesn(Pf−Pn)ψlk≤CeCs2+C∣s∣/Π(Dn∣Xn). No translation invariance of Dn is used.

4.1F2F7step 3.1algebra

Put Zlk=n⟨f−Pn,ψlk⟩ for l≤Ln and pn=Π(Dn∣Xn). Exponential Markov with s=±λl gives ΠD{∣Zlk∣>uλl}≤Cpn−1e−λl(u−C). Union over the at most C2l locations shows EΠDmax⁡k∣Zlk∣≤Cpn−1λl. Union also over levels and integrate in u above a sufficiently large constant to obtain EΠDsup⁡l≤Ln,k∣Zlk∣/λl≤C/pn: the relevant integral is bounded by Cpn−1∑l≥12l∫M∞e−l(u−C)du, plus a finite low-level term. Also the wavelet level bound and a geometric sum give EΠD∥PLn(f−Pn)∥∞≤Cpn−1dλLn/n.

4.2F1step 1.1step 2.1step 3.1algebra

Fix a finite linear combination γ of wavelets and a fixed real s. Repeat step 2.1 with this bounded γ. Its remainder is now o(1), and Var⁡fγ→Var⁡0γ uniformly on Dn. The prior translation involves finitely many fixed coordinates, and its density ratio tends to one uniformly on Dn: use the global S1 log-Lipschitz bound or the fixed Gaussian precision block and bounded quotient coordinates in S2. Let As be the translated image of Dn. For large n, As contains Dn−:={∥θ−θ∗∥2≤bnen/2} because the translation has norm O(n−1/2)=o(bnen). Both Π(Dn−∣Xn) and Π(Dn∣Xn) tend to one by [F1]. Bounding the translated integral above by the full normalizer and below by its integral on Dn− therefore gives EΠDesn(Pf−Pn)γ→es2Var⁡0(γ)/2 in probability.

5.1F2F5F7step 4.1algebra

Each empirical wavelet coordinate has variance at most D0/n and summands bounded by C2l/2. Bernstein [F5] gives Pr⁡{∣(Pn−P0)ψlk∣>C[t/n+2l/2t/n]}≤2e−t. Choose t=C′(l+1)+u, union over k, and integrate over u≥0 to get Emax⁡k∣(Pn−P0)ψlk∣≤C[λl/n+2l/2λl/n]. Summing against 2l/2 yields ∥PLn(Pn−P0)∥∞=OP(dλLn/n+dλLn/n)=OP(dλLn/n), since dλLn/n→0. Moreover ∥PLnf0−f0∥∞≤Cd−α≤CdλLn/n for both cutoffs. Consequently the posterior projected density error is tight at rate an=dλLn/n.

5.2F3F6F7step 4.2algebra

Here is the needed finite-dimensional Laplace continuity argument. Along any subsequence, extract a further subsequence on which the preceding transform convergences hold almost surely for every rational s and every rational vector of finite-coordinate coefficients, using countability and convergence in probability. The transforms at the positive and negative coordinate unit vectors give tightness of these deterministic finite-dimensional laws by exponential Markov and a finite union bound. [F6] gives a weakly convergent further subsequence. For a fixed rational direction and rational s, its exponential is uniformly integrable: its second moment is bounded by the transform at 2s, and Cauchy–Schwarz and Markov bound the expectation above any large cutoff. Truncation thus passes its transform to the weak limit. In each coordinate direction and then any rational linear direction, the limit has finite exponential moments of every rational order, and hence of every real order by bounding et∣x∣ by eqx+e−qx for rational q>∣t∣. Its moment generating function is analytic: on every bounded complex disk its power series can be integrated term by term under eq∣x∣. Equality with the Gaussian transform on the rationals therefore gives equality of all moments by the real power series at zero. Integrating the characteristic-function power series under the same exponential bound gives the Gaussian characteristic function. [F6] identifies every rational linear projection with the corresponding centered normal. Continuity of characteristic functions in their vector argument extends the identification to real vectors; [F6] then identifies the finite-dimensional law with the Gaussian projection of [F3]. Every weakly convergent further subsequence has that limit, so tightness implies weak convergence of the full deterministic subsequence, and [F7] gives bounded-Lipschitz convergence. The initial subsequence argument proves convergence in probability of the original random projected laws.

5.3F7givenstep 4.1algebra

For the coefficients through Ln, step 4.1 and Markov give posterior tightness of sup⁡l≤Ln,k∣Zlk∣/λl. Therefore for J<Ln, the M(w) norm of the part with J<l≤Ln is at most this variable times sup⁡l>Jλl/wl, which tends to zero as J→∞ by admissibility. This proves the required uniform projected posterior tail bound.

6.1F2step 1.1step 5.1algebra

This projected rate controls the full supremum error. Put h=θ−θ∗, f∗=eθ∗/∫eθ∗, and v=h−Pf∗h∈VLn. Since ∫h=0, ∥h∥∞≤2∥v∥∞. Normalized exponential expansion gives f−f∗=f∗v+R with ∥R∥∞≤C∥h∥∞2 on Dn. Also ∥f∗−f0∥∞≤Cd−α. For any fixed 0<β<min⁡(α,1), f0 is β-Hölder, so [F2] gives ∥PLn(f0v)−f0v∥∞≤Cd−β∥v∥∞. The lower bound f0≥ρ0 and uniform boundedness of PLn imply c∥h∥∞≤∥PLn(f−f0)∥∞+Cd−β∥h∥∞+C∥h∥∞2+Cd−α. Step 1.1 makes the two terms proportional to ∥h∥∞ absorbable. It follows that ∥f−f0∥∞≤C[∥PLn(f−f0)∥∞+d−α] uniformly on Dn. Thus the full posterior supremum error is tight at rate an.

7.1F2givenstep 6.1algebra

Choose Mn→∞ so slowly that MnλLn/wLn→0. Step 6.1 makes the posterior probability of ∥f−f0∥∞>Mnan tend to zero. On its complement, the L1 wavelet bound and monotonicity of w give n∥P>Ln(f−f0)∥M(w)≤Cn2−Ln/2wLn−1Mnan≤CMnλLn/wLn→0. The truth coefficients satisfy n∥P>Lnf0∥M(w)≤Cnd−α−1/2/wLn≤CλLn/wLn→0 for either cutoff. Hence the entire density tail above Ln is negligible in posterior probability.

8.1F3F4step 1.1step 5.2step 5.3step 7.1algebra∎

Each density is a finite exponential of bounded continuous functions, hence belongs to L2; its coefficients, and those of Pn(Ln), belong to M0(w). Removing Dn changes posterior integrals of functions bounded by one by at most 2[1−Π(Dn∣Xn)]=oP(1). Step 5.2 supplies fixed finite-projection convergence to [F3], and steps 5.3, 7.1 supply the posterior-tail condition. Apply [F4] to conclude the asserted bounded-Lipschitz convergence in M0(w).

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CDF and multiscale credible-band calibration from weak BvM limits

Statement

Let P0 have a density f0 on [0,1] bounded above and bounded away from zero, and put F0(t)=∫0tf0(x)dx. Use the wavelet basis and M0(w) of Little-o multiscale coefficient space M0(w), and assume the wavelet conditions and summability condition ∑lwl2−l/2<∞ of The multiscale primitive map is continuous into C[0,1]. Let Tn be a measurable L2-valued center, let Πn be a posterior kernel supported on L2 densities, and define Qn to be the conditional law on M0(w) of n(f−Tn) under f∼Πn(⋅∣Xn).

Assume under P0n that (i) Qn converges in bounded-Lipschitz distance in probability to the centered Gaussian bridge coefficient law GP0 in M0(w), whose finite coefficient covariances are P0[(h−P0h)(g−P0g)], and (ii) n(Tn−f0)⇒GP0 in M0(w). For u=1−α, let qM and qC be the lower u-quantiles of ∥GP0∥M(w) and ∥JGP0∥∞. Assume both CDFs are continuous on R and strictly increasing on open neighborhoods of their respective quantiles, and that qM,qC>0. These local quantile conditions allow the CDFs to be constant on the negative half-line. In the projected empirical-center case Tn=Pn(Ln), Projected empirical bridge CLT in the little-o multiscale space supplies premise (ii) under its stated smoothness and cutoff conditions. For the source-specific type-S and type-H priors, the posterior BvM premise (i) is established in Type-S density posteriors satisfy the weak multiscale Bernstein–von Mises theorem and Type-H histogram posterior weak Bernstein–von Mises theorem, respectively.

For a posterior draw f, write Ff=Jf and FTn=JTn, where J is the primitive map of The multiscale primitive map is continuous into C[0,1]. Then the posterior law of n(Ff−FTn) converges in bounded-Lipschitz distance on C([0,1]) to the P0-Brownian bridge BP0(t), with covariance F0(s∧t)−F0(s)F0(t).

For 0<α<1, let RnM and RnC be the posterior lower 1−α quantiles of ∥n(f−Tn)∥M(w) and ∥n(Ff−FTn)∥∞, respectively. The corresponding posterior balls CnM={f:∥f−Tn∥M(w)≤RnM/n},CnC={F:∥F−FTn∥∞≤RnC/n} are measurable credible sets of posterior mass at least 1−α. Their frequentist coverage tends to 1−α, and the scaled radii converge to the respective 1−α quantiles of ∥GP0∥M(w) and ∥BP0∥∞.

Facts & Assumptions

Given: The density law, posterior kernel, wavelet basis, space M0(w), primitive map, two weak-convergence assumptions, continuous strictly increasing limit norm CDFs, and 0<α<1 in the Statement.

[F1]

Little-o multiscale coefficient space M0(w): M0(w) has the weighted supremum norm on wavelet coefficients whose normalized level maxima vanish.

[F2]

The multiscale coefficient space is separable and has vanishing projection tails: every square-summable wavelet coefficient sequence belongs to M0(w).

[F3]

The multiscale primitive map is continuous into C[0,1]: J:M0(w)→C([0,1]) is continuous and agrees with f↦(t↦∫0tf) for L2 functions.

[F4]

Continuous mapping theorem: a continuous map carries weak convergence of probability laws to weak convergence of their pushforwards.

[F5]

Posterior quantiles are measurable and bracket their probability level: for a posterior probability kernel on R, its lower u-quantile is measurable and its CDF brackets u.

[F6]

Posterior quantiles stabilize under scalar weak convergence: if the limiting scalar CDF is continuous on R and strictly increasing on a neighborhood of the target quantile, bounded-Lipschitz convergence in probability implies convergence of that posterior quantile.

[F7]

Posterior credible set: a graph-measurable rule whose posterior mass is at least 1−α is a posterior credible set at level 1−α.

[A1]

The posterior laws Qn converge in bounded-Lipschitz distance in probability to the centered Gaussian bridge coefficient law GP0 in M0(w).

[A2]

The sampling centers satisfy n(Tn−f0)⇒GP0 in M0(w).

[A3]

The CDFs of ∥GP0∥M(w) and ∥JGP0∥∞ are continuous on R and strictly increasing on open neighborhoods of their positive 1−α quantiles. Continuity at each lower quantile q implies its CDF value is 1−α.

[F8]

Portmanteau theorem: weak convergence of probability measures gives convergence of probabilities of sets whose boundary has zero limit measure.

[F9]

Projected empirical bridge CLT in the little-o multiscale space: for the projected empirical center and the theorem's coefficient regularity and cutoff assumptions, n(Pn(Ln)−f0)⇒GP0 in M0(w).

[F11]

Logarithmic negative Sobolev spaces for white noise: the wavelets form a complete orthonormal basis of L2([0,1]), so finite orthogonal projections converge in L2.

[F12]

Cauchy-Schwarz for random variables: square-integrable random variables satisfy ∣E[UV]∣≤(EU2EV2)1/2.

Proof

1.1A1F3F11F12givenalgebra

The posterior draw f and center Tn are L2-valued, so [F2] embeds n(f−Tn) in M0(w); [F1] supplies its norm. For an L-Lipschitz map T between metric spaces and any admissible bounded 1-Lipschitz test h on its target, h∘T/max⁡(1,L) is an admissible test on its domain. Therefore βBL(T#ν,T#ρ)≤max⁡(1,L)βBL(ν,ρ). By [F3], J is linear and Lipschitz with a finite constant LJ. The bound applied pointwise to the data-indexed laws in [A1] gives βBL(J#Qn,J#GP0)→0 in probability. Moreover, if ℓ:C([0,1])→R is continuous and linear, then ℓ∘J is continuous and linear on M0(w). The centered Gaussian premise on GP0 says exactly that this scalar pushforward is centered normal, allowing zero variance. Thus J#GP0 is a centered Gaussian Borel law. In particular, for any finite t1,…,tm and real a1,…,am, the functional x↦∑iaiJx(ti) is continuous and linear, so the evaluation vector (JGP0(ti))i=1m is jointly centered Gaussian. This uses only the scalar Gaussian pushforward meaning of the premise, without characteristic-function uniqueness or a Gaussian existence theorem. To identify its covariance, let pJ1[0,s] be the finite wavelet projection of the indicator. The finite Gaussian coefficient covariance gives Cov⁡(J(PJGP0)(s),J(PJGP0)(t))=P0[(pJ1[0,s]−P0pJ1[0,s])(pJ1[0,t]−P0pJ1[0,t])]. By [F11], pJ1[0,s]→1[0,s] in Lebesgue L2; since f0≤B, this is also convergence in L2(P0). The variance of a difference of two finite projected Gaussian evaluations is the P0-variance of the corresponding difference of projected indicators, so it tends to zero; hence those evaluations are Cauchy in L2. They also converge almost surely to JGP0(s) because PJGP0→GP0 in M0(w) and J is continuous. The almost-sure and in-probability limits coincide: for any ε>0, the probability that they differ by more than ε is bounded by the two probabilities that each sequence differs from its limit by more than ε/2, both tending to zero. If UJ,VJ are the projected evaluations and U,V their L2 limits, [F12] gives ∣E[UJVJ]−E[UV]∣≤∥UJ−U∥2∥VJ∥2+∥U∥2∥VJ−V∥2⟶0; the norms ∥VJ∥2 are bounded because VJ→V in L2, and the means converge to zero as well. Thus the finite covariance passes to the limit. The resulting covariance is P0[(1[0,s]−F0(s))(1[0,t]−F0(t))]=F0(s∧t)−F0(s)F0(t), the defining covariance of the P0-Brownian bridge.

1.2F5F7givenalgebra

The posterior pushforward under either norm is a probability kernel on [0,∞). By [F5], the two lower quantiles are measurable and their posterior CDFs at those radii are at least 1−α. Since the centers and norms are measurable, the membership graphs of CnM and CnC are measurable. Thus both sets are credible by [F7].

2.1A1A2A3F1F6F9step 1.1

The norm maps x↦∥x∥M(w) and F↦∥F∥∞ are 1-Lipschitz by the reverse triangle inequality. Applying the pushforward bound of step 1.1 first to the M(w) norm and then to the supremum norm after J gives bounded-Lipschitz convergence in probability of both posterior norm laws to their corresponding limit norm laws. Their CDFs satisfy [A3], so [F6] gives RnM→qM and RnC→qC in probability. For the projected empirical center Tn=Pn(Ln), [F9] verifies [A2] under the smoothness and cutoff assumptions in [F9].

3.1A2A3F3F4F8step 2.1algebra∎

By [A2] and [F4], n(Tn−f0)⇒GP0 and its primitive converges weakly to BP0. The frequentist error uses the negative center difference, but ∥f0−Tn∥M(w)=∥Tn−f0∥M(w) and ∥J(f0−Tn)∥∞=∥J(Tn−f0)∥∞ because J is linear. Thus each scaled frequentist error norm converges to the corresponding limit norm in [A3]. On the event that the random radius is within ε of its deterministic limit from step 2.1, coverage is bounded above and below by probabilities for the frequentist norm with fixed thresholds expanded or contracted by ε. [F8] gives convergence of those fixed-threshold probabilities because [A3] makes their boundary probabilities zero. Sending ε↓0 and using the CDF value 1−α at its quantile from [A3] yields 1−α for both coverage probabilities. This comparison does not require independence between the data-dependent posterior radii and the frequentist center.

TheoremStatement: Literature-sourcedProof: AI-adaptedOpen item page →

Diameter of undersmoothed multiscale credible bands

Statement

Assume all hypotheses of CDF and multiscale credible-band calibration from weak BvM limits at a fixed credibility level 1−α, 0<α<1, and use its M0(w) credible ball CnM and scaled radius RnM. Let γ>0, assume the compactly supported wavelets have uniformly bounded overlap and ∥ψlk∥∞≤C2l/2, and define ∥f∥Cψγ:=sup⁡l,k2l(γ+1/2)∣⟨f,ψlk⟩∣. Suppose ∥f0∥Cψγ<∞. Choose integers jn with 2jn≍(n/log⁡n)1/(2γ+1) and let un=wjn/jn→∞. Intersect the credible ball with the coefficient smoothness ball: C‾n=CnM∩{f:∥f∥Cψγ≤un}. Then Pf0(n){f0∈C‾n}→1−α, and its L∞ diameter satisfies diam⁡L∞(C‾n)=OPf0(n) ⁣((n/log⁡n)−γ/(2γ+1)un).

Facts & Assumptions

Given: All hypotheses, the credible ball and radius of CDF and multiscale credible-band calibration from weak BvM limits, the coefficient smoothness norm and wavelet assumptions in the Statement, γ>0, and un→∞.

[F1]

Little-o multiscale coefficient space M0(w): the multiscale ball bounds each level-l coefficient by wl times its radius.

[F2]

CDF and multiscale credible-band calibration from weak BvM limits: CnM has frequentist coverage tending to 1−α, and its scaled radius RnM converges in probability to a finite quantile, hence is OP(1).

[L1]

The Statement defines Cψγ by the displayed coefficient norm sup⁡l,k2l(γ+1/2)∣⟨f,ψlk⟩∣.

Proof

1.1F2L1given

Since ∥f0∥Cψγ<∞ and un→∞, [L1] implies the truth belongs to the coefficient smoothness ball for all sufficiently large n. For those n, {f0∈C‾n}={f0∈CnM}, so the asserted coverage follows from [F2].

1.2F1L1givenalgebra

Let f,g∈C‾n. For l≤jn, [F1] gives max⁡k∣flk−glk∣≤2RnMwl/n. For l>jn, [L1] and membership in the coefficient smoothness ball give max⁡k∣flk−glk∣≤2un2−l(γ+1/2). At each point, only a uniformly bounded number of level-l wavelets are nonzero, each bounded by C2l/2. Therefore the low-frequency contribution to ∥f−g∥∞ is at most CRnMn−1/2∑l≤jn2l/2wl, and the high-frequency contribution is at most Cun∑l>jn2−lγ. These series also give uniformly convergent representatives because γ>0.

2.1step 1.2algebra

Since wl is nondecreasing, ∑l≤jn2l/2wl≤C2jn/2wjn by summing a geometric series. Also ∑l>jn2−lγ≤Cγ2−jnγ. The first bound in step 1.2 is thus at most CRnMwjn2jn/2/n=CRnMunjn2jn/2/n.

3.1F2step 1.2step 2.1algebra∎

The relation 2jn≍(n/log⁡n)1/(2γ+1) implies both 2−jnγ≍(n/log⁡n)−γ/(2γ+1) and jn2jn/2/n≤Cγ(n/log⁡n)−γ/(2γ+1). Combining the low- and high-frequency bounds in steps 1.2 and 2.1 and using RnM=OP(1) from [F2] yields the stated diameter bound.

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Type-S and Type-H density credible bands have asymptotically exact coverage

Statement

Assume AC. Use either Type-S1, Type-S2 or Type-H with all the truth, basis, prior-scale, Dirichlet-parameter and cutoff conditions of Type-S log-density and type-H histogram prior families. Let wl≥1 be nondecreasing, wl/l+1→∞, and ∑lwl2−l/2<∞. In Type S take Tn=Pn(Ln), the empirical wavelet projection through level Ln. In Type H take the empirical histogram Tn=hn at mesh 2−Ln, equivalently the Haar projection with scaling coordinate and details l<Ln.

For each 0<η<1, the posterior multiscale and CDF balls of CDF and multiscale credible-band calibration from weak BvM limits, at posterior level 1−η and centered at these Tn, have posterior mass at least 1−η and frequentist coverage tending to 1−η. Their scaled radii converge in probability to the positive finite 1−η quantiles of the corresponding Gaussian bridge norms. In particular, writing Fh(t)=∫0th(x)dx, the posterior law of n(Ff−FTn) converges in bounded-Lipschitz distance on C([0,1]) to the P0-Brownian bridge law, in P0n-probability.

If additionally the coefficient smoothness and undersmoothing hypotheses of Diameter of undersmoothed multiscale credible bands hold, its intersection with the stated coefficient smoothness ball has the same limiting coverage and the diameter bound asserted there. No unverified entropy, prior-mass, posterior contraction or quantile-regularity premise is required in this corollary.

Facts & Assumptions

Given: AC, one of the three source-specific prior regimes, the specified empirical center, admissible summable weights, and 0<η<1.

[A1]

The Axiom of Choice is inherited from the following suppliers.

[F1]

Type-S density posteriors satisfy the weak multiscale Bernstein–von Mises theorem and Type-H histogram posterior weak Bernstein–von Mises theorem prove posterior bounded-Lipschitz convergence about the respective empirical projections, to the Borel Gaussian bridge with covariance P0[(ψ−P0ψ)(ψ′−P0ψ′)].

[F2]

Compact wavelet projections approximate smooth functions and commute asymptotically with multiplication preserves coefficient regularity of eg at every positive order, including integers. Projected empirical bridge CLT in the little-o multiscale space proves the sampling CLT for bounded truths with coefficient smoothness γ>1/2 and either cutoff regime.

[F3]

Continuous and strictly increasing norm distributions for density bridges proves that both bridge norm CDFs are continuous and strictly increasing on positive arguments and have unique positive finite interior quantiles, under the given positive bounded truth and primitive-map summability conditions.

[F4]

CDF and multiscale credible-band calibration from weak BvM limits gives measurable credible balls, CDF pushforward convergence, radius limits and exact asymptotic coverage from posterior BvM, the sampling-center CLT and the stated norm-quantile conditions.

[F5]

Diameter of undersmoothed multiscale credible bands gives the additional smoothness-ball coverage and diameter conclusion under its explicit coefficient smoothness and undersmoothing assumptions.

Proof

1.1A1F1F2givenalgebra

In Type S, [F1] proves posterior BvM about Tn=Pn(Ln) with the locally proved S1 range α>1 and Gaussian S2 range α>1/2, 0<r<α−1/4. The truth g0=log⁡f0 has α coefficient regularity, so [F2] gives that regularity for f0=eg0 as well. The retained basis has the support, overlap and supremum bounds required by the empirical-process theorem in [F2]. Taking γ=α>1/2 and the given cutoff therefore proves its sampling-center CLT with the same Gaussian bridge.

1.2F1F2givenalgebra

In Type H, [F1] proves posterior BvM about the empirical histogram hn. Haar wavelets have the same support, overlap and supremum bounds. The ordinary α-Hölder truth, 1/2<α≤1, has Haar coefficients bounded by C2−l(α+1/2): subtract its value at one point of the support in the coefficient integral, use the zero mean, support diameter 2−l and L1 norm 2−l/2. The histogram projection retains details through Jn=Ln−1. Both given cutoff regimes remain true with this Jn, since multiplying 2Ln by 1/2 changes only their comparison constants. Thus [F2] with γ=α gives the sampling CLT about this exact histogram center. The finite scaling coordinate is included and its centered fluctuation is zero.

2.1F1F3F4step 1.1step 1.2given

In all three cases, positivity and boundedness of f0, admissibility, and the displayed summability verify [F3]. Hence every norm-quantile assumption of [F4] holds at u=1−η. Steps 1.1, 1.2 verify its posterior and sampling premises, with the same coefficient covariance law. Applying [F4] proves all asserted CDF limits, measurable credibility, radius limits and frequentist coverage, for the exact empirical centers and every 0<η<1.

3.1F5step 2.1given∎

When the additional hypotheses in the last paragraph of the Statement hold, the multiscale credible ball just obtained is precisely the input to [F5]. Applying that theorem yields its smoothness-intersection coverage and stated diameter rate. These are additional hypotheses only for this diameter conclusion; the coverage and CDF conclusions in step 2.1 required no such extra conditions.

5 · Examples, counterexamples and false statements

None yet.

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