Abstract: (i) Change point detection for networks: We consider the preferential attachment model. We formulate and study the regime where the network transitions from one evolutionary scheme to another. In the large network limit we derive asymptotics for various functionals of the network including degree distribution and maximal degree. We study functional central limit theorems for the evolution of the degree distribution which feed into proving consistency of a proposed estimator of the change point. (ii) Power of choice and network…

 Abstract: We propose an efficient meta-algorithm for Bayesian inference problems based on low-degree polynomials, semidefinite programming, and tensor decomposition. The algorithm is inspired by recent lower bound constructions for sum-of-squares and related to the method of moments. Our focus is on sample complexity bounds that are as tight as possible (up to additive lower-order terms) and often achieve statistical thresholds or conjectured computational thresholds. Our algorithm recovers the best known bounds for partial recovery in the stochastic block model, a…

Abstract: Active learning is a framework for supervised learning that explicitly models, and permits one to control and optimize, the costs of labeling data. The hope is that by carefully selecting which examples to label in an adaptive manner, the number of labels required to learn an accurate classifier is substantially reduced. However, in many learning settings (e.g., when some classes are rare), it is difficult to identify which examples are most informative to label, and existing active learning algorithms are prone to labeling uninformative examples. Based…

Abstract: We describe an emerging research direction regarding the complexity of testing global properties of discrete distributions, when given access to only a few samples from the distribution. Such properties might include testing if two distributions have small statistical distance, testing various independence properties, testing whether a distribution has a specific shape (such as monotone decreasing, k-modal, k-histogram, monotone hazard rate,...), and approximating the entropy. We describe bounds for such testing problems whose sample complexities are sublinear in the size…

Abstract: Spin systems on trees have found applications ranging from the reconstruction of phylogenies to the analysis of networks with community structure. A key feature of such processes is the interplay between the growth of the tree and the decay of correlations along it. How the resulting threshold phenomena impact estimation depends on the problem considered. I will illustrate this on two recent results: 1) the critical threshold of ancestral sequence reconstruction by maximum parsimony on general phylogenies and 2)…

Abstract: Why are we interested in the causal structure of a process? In classical prediction tasks, for example, it seems that no causal knowledge is required. In many situations, however, we are interested in a system's behavior after parts of this system have been changed. Here, causal models become important because they are usually considered invariant under those changes. A causal prediction (which uses only direct causes of the target variable as predictors) remains valid even if we intervene on…

Abstract: We consider the problem of bandit optimization, inspired by stochastic optimization and online learning with bandit feedback. In this problem, the objective is to minimize a global, not necessarily cumulative, convex loss function. This framework allows us to study a very general class of problems, with applications in statistics, machine learning, and other fields. To solve this problem, we analyze the Upper-Confidence Frank-Wolfe algorithm, inspired by techniques ranging from bandits to convex optimization. We identify slow and fast of…

Abstract: A common theme in machine learning is succinct modeling of distributions over large domains. Probabilistic graphical models are one of the most expressive frameworks for doing this. The two major tasks involving graphical models are learning and inference. Learning is the task of calculating the "best fit" model parameters from raw data, while inference is the task of answering probabilistic queries for a model with known parameters (e.g. what is the marginal distribution of a subset of variables, after…