Learning Graphical Models
Reviews: Information Theoretic Properties of Markov Random Fields, and their Algorithmic Applications
This paper is concerned with learning Markov random fields (MRF). It is a theoretical paper, which is ultimately focused with proving a particular statement: given a variable X in an MRF, and given some of its Markov blanket variables B, there exists another variable Y that is conditionally dependent on X given the subset of B. In general this statement is not true; so the goal here is to identify some conditions where this is true. Most of this paper is centered around this, from which the ability to learn an MRF follows. The paper is mostly technical; my main complaint is that I do not think it is very intuitive. It appears that central to the results is the assumption on non-degeneracy, which I believe should be explained in higher level terms.
Reviews: Deep Homogeneous Mixture Models: Representation, Separation, and Approximation
The paper discusses connections between multiple density models within the unifying framework of homogeneous mixture models: tensorial mixtures models [1], hidden Markov models, latent tree models and sum-product networks [2] are discussed. The authors argue that there is a hierarchy among these models by showing that a model lower in the hierarchy can be cast into a model higher in the hierarchy using linear size transformations. Furthermore, the paper gives new theoretical insights in depth efficiency in these models, by establishing a connection between properties of the represented mixture coefficient tensor (e.g. Finally, the paper gives positive and somewhat surprising approximation results using [3]. Strengths: connections between various models, which so far were somewhat folk wisdom, are illustrated a unifying tensor mixture framework.
Reviews: Lifted Weighted Mini-Bucket
The paper proposes a lifted version of the weighted mini-bucket inference algorithm. Weighted mini-bucket is a variant of Variable Elimination that can trade off computational cost (e.g., achieving runtime sub-exponential in the treewidth) for accuracy. It essentially uses Holder inequality and variational approximations to represent "messages" that do not fit in the available memory budget. The main idea is to extend the approach to relational models (e.g., Markov Logic Networks) to take advantage of the additional structure, specifically, the fact that ground factors are produced from first-order templates and therefore share significant structure. The work appears to be solid, but it is difficult to parse.
Reviews: Near-Optimal Time and Sample Complexities for Solving Markov Decision Processes with a Generative Model
In this paper the authors present PAC-RL results for finite-spaces discounted MDP with a generative sampling model (which can generate in O(1) time a state transition for each given state-action pair). They introduce a value-iteration type algorithm for finding an \epsilon -optimal policy, and prove that its running time and sample complexity are nearly the best possible and match, up to logarithmic factors, the lower bounds established previously in [AMK13]. These results are significant: They improve over a recent result in [SWWY18] by a factor of (1 - \gamma) {-1} ( \gamma is the discount factor), and they also fill a known gap in the earlier results of [AMK13] regarding the sample complexity of finding a near-optimal policy. Both the algorithm and its analysis are very interesting. They build upon the prior work [AMK13] and [SWWY18], and combine the algorithmic ideas and proof techniques from both papers in a highly non-trivial and original way.
Reviews: Cluster Variational Approximations for Structure Learning of Continuous-Time Bayesian Networks from Incomplete Data
The paper introduces a generalization of previous variational methods for inference with jumps processes; here, the proposal approximating measure to the posterior relies on a star approximation. In application to continuous-time Bayesian networks, this means isolating clusters of nodes across children and parents, in order to build an efficient approximation to the traditional variational lower bound. The paper further presents examples and experiments that show how the proposed approach can be adapted to structure learning tasks in continuous-time settings. This is an interesting and topical contribution likely to appeal to the statistical and probabilistic community within NIPS. The paper is, in overall, well-written and reasonably well-structured. It offers a good background on previous work, helps the reader to understand its relevance and put its results in context within the existing literature.
Reviews: Clone MCMC: Parallel High-Dimensional Gaussian Gibbs Sampling
This paper proposes a new parallel approximate sampler for high-dimensional Gaussian distributions. The algorithm is a special case of a larger class of iterative samplers based on a transition equation (2) and matrix splitting that is analysed in [9]. The algorithm is similar to the Hogwild sampler in term of the update formula and the way of bias analysing, but it is more flexible in the sense that there is a scalar parameter to trade-off the bias and variance of the proposed sampler. I appreciate the detailed introduction about the mathematical background of the family of sampling algorithms and related works. It is also easy to follow the paper and understand the merit of the proposed algorithm. The illustration of the decomposition of the variance and bias in Figure 1 gives a clear explanation about the role of \eta.
Reviews: Nonparametric learning from Bayesian models with randomized objective functions
The idea: You want to do Bayesian inference on a parameter theta, with prior pi(theta) and parametric likelihood f_theta, but you're not sure if the likelihood is correctly specified. So put a nonparametric prior on the sampling distribution: a mixture of Dirichlet processes centered at f_theta with mixing distribution pi(theta). The concentration parameter of the DP provides a sliding scale between vanilla Bayesian inference (total confidence in the parametric model) and Bayesian bootstrap (no confidence at all, use the empirical distribution). This is a simple idea, but the paper presents it lucidly and compellingly, beginning with a diverse list of potential applications: the method may be viewed as regularization of a nonparametric Bayesian model towards a parametric one; as robustification of a parametric Bayesian model to misspecification; as a means of correcting a variational approximation; or as nonparametric decision theory, when the log-likelihood is swapped out for an arbitrary utility function. As for implementation, the procedure requires (1) sampling from the parametric Bayesian posterior distribution and (2) performing a p-dimensional maximization, where p is the dimension of theta.
Reviews: Generalizing Tree Probability Estimation via Bayesian Networks
In this paper the authors propose an efficient method for tree probability estimation (given a collection of trees) that relies on the description of trees as subsplit Bayesian networks. Through this representation, the authors relax the classic conditional clade distribution - which assumes that given their parent, sister clades are independent - and assume instead that given their parent subsplit, sister subsplits are independent, thus allowing more dependence structure on sister clades. The authors first present a simple maximum likelihood estimation algorithm for rooted trees, and then propose two alternatives to generalize their work to unrooted trees. They finally illustrate their method on both simulated and real-data experiments. I think this paper is very well written, in particular I have greatly appreciated the Background and SBN description sections that make use of a simple though not trivial example to introduce new notions and provide useful insights on the assumptions.
A New Architecture for Neural Enhanced Multiobject Tracking
Wei, Shaoxiu, Liang, Mingchao, Meyer, Florian
Multiobject tracking (MOT) is an important task in robotics, autonomous driving, and maritime surveillance. Traditional work on MOT is model-based and aims to establish algorithms in the framework of sequential Bayesian estimation. More recent methods are fully data-driven and rely on the training of neural networks. The two approaches have demonstrated advantages in certain scenarios. In particular, in problems where plenty of labeled data for the training of neural networks is available, data-driven MOT tends to have advantages compared to traditional methods. A natural thought is whether a general and efficient framework can integrate the two approaches. This paper advances a recently introduced hybrid model-based and data-driven method called neural-enhanced belief propagation (NEBP). Compared to existing work on NEBP for MOT, it introduces a novel neural architecture that can improve data association and new object initialization, two critical aspects of MOT. The proposed tracking method is leading the nuScenes LiDAR-only tracking challenge at the time of submission of this paper.
Robust Domain Generalisation with Causal Invariant Bayesian Neural Networks
Gendron, Gaël, Witbrock, Michael, Dobbie, Gillian
Deep neural networks can obtain impressive performance on various tasks under the assumption that their training domain is identical to their target domain. Performance can drop dramatically when this assumption does not hold. One explanation for this discrepancy is the presence of spurious domain-specific correlations in the training data that the network exploits. Causal mechanisms, in the other hand, can be made invariant under distribution changes as they allow disentangling the factors of distribution underlying the data generation. Yet, learning causal mechanisms to improve out-of-distribution generalisation remains an under-explored area. We propose a Bayesian neural architecture that disentangles the learning of the the data distribution from the inference process mechanisms. We show theoretically and experimentally that our model approximates reasoning under causal interventions. We demonstrate the performance of our method, outperforming point estimate-counterparts, on out-of-distribution image recognition tasks where the data distribution acts as strong adversarial confounders.