1. VEEGAN: Reducing Mode Collapse in GANs using Implicit Variational Learning

Authors Akash Srivastava, Lazar Valkov, Chris Russell, Michael Gutmann and Charles Sutton

Abstract

Deep generative models provide powerful tools for distributions over complicated manifolds, such as those of natural images. But many of these methods, including generative adversarial networks (GANs), can be difficult to train, in part because they are prone to mode collapse, which means that they characterize only a few modes of the true distribution. To address this, we introduce VEEGAN, which features a reconstructor network, reversing the action of the generator by mapping from data to noise. Our training objective retains the original asymptotic consistency guarantee of GANs, and can be interpreted as a novel autoencoder loss over the noise. In sharp contrast to a traditional autoencoder over data points, VEEGAN does not require specifying a loss function over the data, but rather only over the representations, which are standard normal by assumption. On an extensive set of synthetic and real world image datasets, VEEGAN indeed resists mode collapsing to a far greater extent than other recent GAN variants, and produces more realistic samples.


2. Autoencoding Variational Inference For Topic Models || Code

Authors: Akash Srivastava and Charles Sutton

Abstract

Topic models are one of the most popular methods for learning representations of text, but a major challenge is that any change to the topic model requires mathematically deriving a new inference algorithm. A promising approach to address this problem is autoencoding variational Bayes (AEVB), but it has proven diffi- cult to apply to topic models in practice. We present what is to our knowledge the first effective AEVB based inference method for latent Dirichlet allocation (LDA), which we call Autoencoded Variational Inference For Topic Model (AVITM). This model tackles the problems caused for AEVB by the Dirichlet prior and by component collapsing. We find that AVITM matches traditional methods in accuracy with much better inference time. Indeed, because of the inference network, we find that it is unnecessary to pay the computational cost of running variational optimization on test data. Because AVITM is black box, it is readily applied to new topic models. As a dramatic illustration of this, we present a new topic model called ProdLDA, that replaces the mixture model in LDA with a product of experts. By changing only one line of code from LDA, we find that ProdLDA yields much more interpretable topics, even if LDA is trained via collapsed Gibbs sampling.


3. Clustering with a Reject Option: Interactive Clustering as Bayesian Prior Elicitation

Authors: Akash Srivastava, James Zou, Ryan P. Adams and Charles Sutton

Abstract

A good clustering can help a data analyst to explore and understand a data set, but what constitutes a good clustering may depend on domain-specific and application specific criteria. These criteria can be difficult to formalize, even when it is easy for an analyst to know a good clustering when she sees one. We present a new approach to interactive clustering for data exploration, called TINDER, based on a particularly simple feedback mechanism, in which an analyst can choose to reject individual clusters and request new ones. The new clusters should be different from previously rejected clusters while still fitting the data well. We formalize this interaction in a novel Bayesian prior elicitation framework. In each iteration, the prior is adapted to account for all the previous feedback, and a new clustering is then produced from the posterior distribution. To achieve the computational efficiency necessary for an interactive setting, we propose an incremental optimization method over data minibatches using Lagrangian relaxation. Experiments demonstrate that TINDER can produce accurate and diverse clusterings.


4. Burst Detection Modulated Document Clustering: A Partially Feature-Pivoted Approach To First Story Detection

Author: Akash Srivastava

Abstract

First Story Detection or FSD is one of the 5 tasks defined under the Topic Detection andTracking program with the purpose to identify the onset of a previously unseen event in a stream of news stories. In this work, we report on the development and evaluation of a feature-pivoted approach to this task. Our method uses the output of a burst detection algorithm to modulate the traditional document clustering based approach to FSD. For burst detection, we work exclusively with words in the input and use a 2 step filtration routine that filters out all the words for which the cumulative term frequencies or the Autocorrelation values of their corresponding signal representations are below a pre-computed threshold. The output is then grouped into sets of words that have similar burst patterns in time. A confidence score is generated for each set of words, quantifying the chance of the set being the first story on the event that it relates to. In the final step all the detected first stories are passed through a restricted clustering unit that uses cosine similarity to cluster together stories that are on the same topic, hence reducing false alarms. Our experiments show that the resultant FSD system performs substantially better than the document-pivoted state-of-art baseline system.