<p>We propose an adaptive neighborhood smoothing estimator for recovering the row-wise connection probabilities in directed sparse graphon models. While standard neighborhood smoothers typically rely on a fixed local bandwidth (e.g., <i>k</i>-nearest neighbors), our approach constructs neighborhoods using a <i>global</i> distance threshold on the outgoing connection profiles derived from the common out-neighbors <InlineEquation ID="IEq1"> <EquationSource Format="TEX">\(\textbf{AA}^\top \)</EquationSource> <EquationSource Format="MATHML"><math> <msup> <mi mathvariant="bold">AA</mi> <mi>⊤</mi> </msup> </math></EquationSource> </InlineEquation> similarity kernel. This global thresholding mechanism yields a spatially adaptive neighborhood size: nodes in homogeneous regions of the latent space automatically aggregate information from a larger number of neighbors, significantly reducing variance, while nodes in complex or transitional regions maintain a minimal neighborhood size to control bias. We establish the first fully non-asymptotic row-wise risk bound for directed sparse graphons, capturing the favorable bias-variance trade-off induced by spatial adaptation. The resulting estimator naturally handles network asymmetry and is shown to outperform fixed-bandwidth benchmarks in simulations. A real-data application and analysis of the <i>C. elegans</i> connectome is presented.</p>

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Spatially adaptive neighborhood smoothing for directed sparse graphons

  • Behzad Aalipur

摘要

We propose an adaptive neighborhood smoothing estimator for recovering the row-wise connection probabilities in directed sparse graphon models. While standard neighborhood smoothers typically rely on a fixed local bandwidth (e.g., k-nearest neighbors), our approach constructs neighborhoods using a global distance threshold on the outgoing connection profiles derived from the common out-neighbors \(\textbf{AA}^\top \) AA similarity kernel. This global thresholding mechanism yields a spatially adaptive neighborhood size: nodes in homogeneous regions of the latent space automatically aggregate information from a larger number of neighbors, significantly reducing variance, while nodes in complex or transitional regions maintain a minimal neighborhood size to control bias. We establish the first fully non-asymptotic row-wise risk bound for directed sparse graphons, capturing the favorable bias-variance trade-off induced by spatial adaptation. The resulting estimator naturally handles network asymmetry and is shown to outperform fixed-bandwidth benchmarks in simulations. A real-data application and analysis of the C. elegans connectome is presented.