22,069 research outputs found
Optimal and Private Learning from Human Response Data
Item response theory (IRT) is the study of how people make probabilistic
decisions, with diverse applications in education testing, recommendation
systems, among others. The Rasch model of binary response data, one of the most
fundamental models in IRT, remains an active area of research with important
practical significance. Recently, Nguyen and Zhang (2022) proposed a new
spectral estimation algorithm that is efficient and accurate. In this work, we
extend their results in two important ways. Firstly, we obtain a refined
entrywise error bound for the spectral algorithm, complementing the `average
error' bound in their work. Notably, under mild sampling conditions,
the spectral algorithm achieves the minimax optimal error bound (modulo a log
factor). Building on the refined analysis, we also show that the spectral
algorithm enjoys optimal sample complexity for top- recovery (e.g.,
identifying the best items from approval/disapproval response data),
explaining the empirical findings in the previous work. Our second contribution
addresses an important but understudied topic in IRT: privacy. Despite the
human-centric applications of IRT, there has not been any proposed
privacy-preserving mechanism in the literature. We develop a private extension
of the spectral algorithm, leveraging its unique Markov chain formulation and
the discrete Gaussian mechanism (Canonne et al., 2020). Experiments show that
our approach is significantly more accurate than the baselines in the
low-to-moderate privacy regime.Comment: International Conference on Artificial Intelligence and Statistics
(AISTATS) 202
Structural origins of the properties of rare earth nickelate superlattices
NiO6 octahedral tilts in the LaNiO3/SrTiO3 superlattices are quantified using
position averaged convergent beam electron diffraction in scanning transmission
electron microscopy. It is shown that maintaining oxygen octahedra connectivity
across the interface controls the octahedral tilts in the LaNiO3 layers, their
lattice parameters and their transport properties. Unlike films and layers that
are connected on one side to the substrate, subsequent LaNiO3 layers in the
superlattice exhibit a relaxation of octahedral tilts towards bulk values. This
relaxation is facilitated by correlated tilts in SrTiO3 layers and is
correlated with the conductivity enhancement of the LaNiO3 layers in the
superlattices relative to individual films.Comment: Accepted for publication in Physical Review B (Rapid Communication
Optimality of Spectral Clustering in the Gaussian Mixture Model
Spectral clustering is one of the most popular algorithms to group high
dimensional data. It is easy to implement and computationally efficient.
Despite its popularity and successful applications, its theoretical properties
have not been fully understood. In this paper, we show that spectral clustering
is minimax optimal in the Gaussian Mixture Model with isotropic covariance
matrix, when the number of clusters is fixed and the signal-to-noise ratio is
large enough. Spectral gap conditions are widely assumed in the literature to
analyze spectral clustering. On the contrary, these conditions are not needed
to establish optimality of spectral clustering in this paper
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