123 research outputs found
Predictive Uncertainty through Quantization
High-risk domains require reliable confidence estimates from predictive
models. Deep latent variable models provide these, but suffer from the rigid
variational distributions used for tractable inference, which err on the side
of overconfidence. We propose Stochastic Quantized Activation Distributions
(SQUAD), which imposes a flexible yet tractable distribution over discretized
latent variables. The proposed method is scalable, self-normalizing and sample
efficient. We demonstrate that the model fully utilizes the flexible
distribution, learns interesting non-linearities, and provides predictive
uncertainty of competitive quality
Graph Convolutional Matrix Completion
We consider matrix completion for recommender systems from the point of view
of link prediction on graphs. Interaction data such as movie ratings can be
represented by a bipartite user-item graph with labeled edges denoting observed
ratings. Building on recent progress in deep learning on graph-structured data,
we propose a graph auto-encoder framework based on differentiable message
passing on the bipartite interaction graph. Our model shows competitive
performance on standard collaborative filtering benchmarks. In settings where
complimentary feature information or structured data such as a social network
is available, our framework outperforms recent state-of-the-art methods.Comment: 9 pages, 3 figures, updated with additional experimental evaluatio
Emerging Convolutions for Generative Normalizing Flows
Generative flows are attractive because they admit exact likelihood
optimization and efficient image synthesis. Recently, Kingma & Dhariwal (2018)
demonstrated with Glow that generative flows are capable of generating high
quality images. We generalize the 1 x 1 convolutions proposed in Glow to
invertible d x d convolutions, which are more flexible since they operate on
both channel and spatial axes. We propose two methods to produce invertible
convolutions that have receptive fields identical to standard convolutions:
Emerging convolutions are obtained by chaining specific autoregressive
convolutions, and periodic convolutions are decoupled in the frequency domain.
Our experiments show that the flexibility of d x d convolutions significantly
improves the performance of generative flow models on galaxy images, CIFAR10
and ImageNet.Comment: Accepted at International Conference on Machine Learning (ICML) 201
Competing interactions in semiconductor quantum dots
We introduce an integrability-based method enabling the study of
semiconductor quantum dot models incorporating both the full hyperfine
interaction as well as a mean-field treatment of dipole-dipole interactions in
the nuclear spin bath. By performing free induction decay and spin echo
simulations we characterize the combined effect of both types of interactions
on the decoherence of the electron spin, for external fields ranging from low
to high values. We show that for spin echo simulations the hyperfine
interaction is the dominant source of decoherence at short times for low
fields, and competes with the dipole-dipole interactions at longer times. On
the contrary, at high fields the main source of decay is due to the
dipole-dipole interactions. In the latter regime an asymmetry in the echo is
observed. Furthermore, the non-decaying fraction previously observed for zero
field free induction decay simulations in quantum dots with only hyperfine
interactions, is destroyed for longer times by the mean-field treatment of the
dipolar interactions.Comment: 10 pages, 5 figures [v2: subsection and references added
Sylvester Normalizing Flows for Variational Inference
Variational inference relies on flexible approximate posterior distributions.
Normalizing flows provide a general recipe to construct flexible variational
posteriors. We introduce Sylvester normalizing flows, which can be seen as a
generalization of planar flows. Sylvester normalizing flows remove the
well-known single-unit bottleneck from planar flows, making a single
transformation much more flexible. We compare the performance of Sylvester
normalizing flows against planar flows and inverse autoregressive flows and
demonstrate that they compare favorably on several datasets.Comment: Published at UAI 2018, 12 pages, 3 figures, code at:
https://github.com/riannevdberg/sylvester-flow
Probing pairing correlations in Sn isotopes using Richardson-Gaudin integrability
Pairing correlations in the even-even A=102-130 Sn isotopes are discussed,
based on the Richardson-Gaudin variables in an exact Woods-Saxon plus reduced
BCS pairing framework. The integrability of the model sheds light on the
pairing correlations, in particular on the previously reported sub-shell
structure.Comment: Proceedings of the XX International School on Nuclear Physics,
Neutron Physics and Applications, Varna, Bulgaria, 16-22 September, 201
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