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A primal-dual method for conic constrained distributed optimization problems

Neural Information Processing Systems

We consider cooperative multi-agent consensus optimization problems over anundirected network of agents, where only those agents connected by an edgecan directly communicate. The objective is to minimize the sum of agent-specific composite convex functions over agent-specific private conic constraintsets; hence, the optimal consensus decision should lie in the intersection of theseprivate sets. We provide convergence rates in sub-optimality, infeasibility andconsensus violation; examine the effect of underlying network topology on theconvergence rates of the proposed decentralized algorithms; and show how to ex-tend these methods to handle time-varying communication networks.


Wasserstein Training of Restricted Boltzmann Machines

Neural Information Processing Systems

Boltzmann machines are able to learn highly complex, multimodal, structured and multiscale real-world data distributions. Parameters of the model are usually learned by minimizing the Kullback-Leibler (KL) divergence from training samples to the learned model. We propose in this work a novel approach for Boltzmann machine training which assumes that a meaningful metric between observations is known. This metric between observations can then be used to define the Wasserstein distance between the distribution induced by the Boltzmann machine on the one hand, and that given by the training sample on the other hand. We derive a gradient of that distance with respect to the model parameters. Minimization of this new objective leads to generative models with different statistical properties. We demonstrate their practical potential on data completion and denoising, for which the metric between observations plays a crucial role.


Understanding Probabilistic Sparse Gaussian Process Approximations

Neural Information Processing Systems

Good sparse approximations are essential for practical inference in Gaussian Processes as the computational cost of exact methods is prohibitive for large datasets. The Fully Independent Training Conditional (FITC) and the Variational Free Energy (VFE) approximations are two recent popular methods. Despite superficial similarities, these approximations have surprisingly different theoretical properties and behave differently in practice. We thoroughly investigate the two methods for regression both analytically and through illustrative examples, and draw conclusions to guide practical application.



Spatio-Temporal Hilbert Maps for Continuous Occupancy Representation in Dynamic Environments

Neural Information Processing Systems

We consider the problem of building continuous occupancy representations in dynamic environments for robotics applications. The problem has hardly been discussed previously due to the complexity of patterns in urban environments, which have both spatial and temporal dependencies. We address the problem as learning a kernel classifier on an efficient feature space. The key novelty of our approach is the incorporation of variations in the time domain into the spatial domain. We propose a method to propagate motion uncertainty into the kernel using a hierarchical model. The main benefit of this approach is that it can directly predict the occupancy state of the map in the future from past observations, being a valuable tool for robot trajectory planning under uncertainty. Our approach preserves the main computational benefits of static Hilbert maps -- using stochastic gradient descent for fast optimization of model parameters and incremental updates as new data are captured. Experiments conducted in road intersections of an urban environment demonstrated that spatio-temporal Hilbert maps can accurately model changes in the map while outperforming other techniques on various aspects.