TechTalks from event: ICML 2011
Hashing with GraphsHashing is becoming increasingly popular for efficient nearest neighbor search in massive databases. However, learning short codes that yield good search performance is still a challenge. Moreover, in many cases real-world data lives on a low-dimensional manifold, which should be taken into account to capture meaningful nearest neighbors. In this paper, we propose a novel graph-based hashing method which automatically discovers the neighborhood structure inherent in the data to learn appropriate compact codes. To make such an approach computationally feasible, we utilize Anchor Graphs to obtain tractable low-rank adjacency matrices. Our formulation allows constant time hashing of a new data point by extrapolating graph Laplacian eigenvectors to eigenfunctions. Finally, we describe a hierarchical threshold learning procedure in which each eigenfunction yields multiple bits, leading to higher search accuracy. Experimental comparison with the other state-of-the-art methods on two large datasets demonstrates the efficacy of the proposed method.
Large Scale Text Classification using Semi-supervised Multinomial Naive BayesNumerous semi-supervised learning methods have been proposed to augment Multinomial Naive Bayes (MNB) using unlabeled documents, but their use in practice is often limited due to implementation difficulty, inconsistent prediction performance, or high computational cost. In this paper, we propose a new, very simple semi-supervised extension of MNB, called Semi-supervised Frequency Estimate (SFE). Our experiments show that it consistently improves MNB with additional data (labeled or unlabeled) in terms of AUC and accuracy, which is not the case when combining MNB with Expectation Maximization (EM). We attribute this to the fact that SFE consistently produces better conditional log likelihood values than both EM+MNB and MNB in labeled training data.
Parallel Coordinate Descent for L1-Regularized Loss MinimizationWe propose Shotgun, a parallel coordinate descent algorithm for minimizing L1-regularized losses. Though coordinate descent seems inherently sequential, we prove convergence bounds for Shotgun which predict linear speedups, up to a problem-dependent limit. We present a comprehensive empirical study of Shotgun for Lasso and sparse logistic regression. Our theoretical predictions on the potential for parallelism closely match behavior on real data. Shotgun outperforms other published solvers on a range of large problems, proving to be one of the most scalable algorithms for L1.
OptiML: An Implicitly Parallel Domain-Specific Language for Machine LearningAs the size of datasets continues to grow, machine learning applications are becoming increasingly limited by the amount of available computational power. Taking advantage of modern hardware requires using multiple parallel programming models targeted at different devices (e.g. CPUs and GPUs). However, programming these devices to run efficiently and correctly is difficult, error-prone, and results in software that is harder to read and maintain. We present OptiML, a domain-specific language (DSL) for machine learning. OptiML is an implicitly parallel, expressive and high performance alternative to MATLAB and C++. OptiML performs domain-specific analyses and optimizations and automatically generates CUDA code for GPUs. We show that OptiML outperforms explicitly parallelized MATLAB code in nearly all cases.