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…

Abstract: In this talk we will first consider a general question of estimating linear functional of the distribution based on the noisy samples from it. We discover that the (two-point) LeCam lower bound is in fact achievable by optimizing bias-variance tradeoff of an empirical-mean type of estimator. Next, we apply this general framework to the specific problem of population recovery. Namely, consider a random poll of sample size n conducted on a population of individuals, where each pollee is asked to…

Abstract: When is simple random walk on growing in time d-dimensional domains recurrent? For domain growth which is independent of the walk, we review recent progress and related universality conjectures about a sharp recurrence versus transience criterion in terms of the growth rate. We compare this with the question of recurrence/transience for time varying conductance models, where Gaussian heat kernel estimates and evolving sets play an important role. We also briefly contrast such expected universality with examples of the rich…

Abstract: Consider the following problem: we monitor a sequence of edgeinsertions and deletions in a graph on n vertices, so there are N = (n choose 2) possible edges (e.g. monitoring a stream of friend accepts/removals on Facebook). At any point someone may say "query()", at which point must output a random edge that exists in the graph at that time from a distribution that is statistically close to uniform.  More specifically, with probability p our edge should come from a distribution close to uniform,…