Finite-sample consistency conjecture for empirical kernel quantile embeddings with p greater than 1

Let XRd\mathcal{X} \subseteq \mathbb{R}^d, let ν\nu have a density, and let PP and QQ be measures on X\mathcal{X} with densities bounded away from zero, satisfying fP(x)cP>0f_P(x) \geq c_P>0 and fP(x)cQ>0f_P(x) \geq c_Q>0. Suppose

EXP[k(X,X)\nicefracp2]<,EXQ[k(X,X)\nicefracp2]<,\mathbb{E}_{X \sim P} [k(X, X)^{\nicefrac{p}{2}}]<\infty, \qquad \mathbb{E}_{X \sim Q} [ k(X, X)^{\nicefrac{p}{2}}]<\infty,

for samples x1:nPx_{1:n} \sim P and y1:nQy_{1:n} \sim Q. Finite-sample consistency conjecture.

Ex1:nPy1:nQe-KQDp(Pn,Qn;ν,γl)e-KQDp(P,Q;ν,γ)=O(l\nicefrac12+n\nicefrac12).\mathbb{E}_{\substack{x_{1:n}\sim P \\ y_{1:n}\sim Q}}\left| \operatorname{e-KQD}_p(P_n, Q_n;\nu, \gamma_l) - \operatorname{e-KQD}_p(P, Q;\nu, \gamma) \right| =\mathcal{O}(l^{-\nicefrac{1}{2}} + n^{-\nicefrac{1}{2}}).

This conjecture predicts an n1/2n^{-1/2}-type finite-sample convergence rate for empirical kernel quantile divergences when p>1p>1, extending the established p=1p=1 argument. The preceding Wasserstein convergence result shows that such a rate requires suitable integrability conditions, and the conjecture remains unproved in the source.

Sources & referencesView supporting material

Primary source

Masha Naslidnyk, Siu Lun Chau, François-Xavier Briol and Krikamol Muandet, “Kernel Quantile Embeddings and Associated Probability Metrics”, arXiv:2505.20433 (2025).

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