Ambuj Tewari

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Nicolò Cesa-Bianchi80
Peter L. Bartlett77
Shai Shalev-Shwartz70
Gábor Lugosi65
Alexander Rakhlin54
35Nicolo Cesa-Bianchi
33Francesco Orabona
32Karthik Sridharan
32Inderjit S. Dhillon
31Alexander Rakhlin

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2002
2017

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On the Consistency of Multiclass Classification Methods
Binary classification is a well studied special case of the classification problem. Statistical properties of binary classifiers, such as consistency, have been investigated in a variety of settings. Binary classification methods can be generalized in many ways to handle multiple classes. It turns out that one can lose consistency in generalizing a binary… (More)
PAC Subset Selection in Stochastic Multi-armed Bandits
We consider the problem of selecting, from among the arms of a stochastic n-armed bandit, a subset of size m of those arms with the highest expected rewards, based on efficiently sampling the arms. This " subset selection " problem finds application in a variety of areas. In the authors' previous work (Kalyanakrishnan & Stone, 2010), this problem is framed… (More)
Learning with Noisy Labels
In this paper, we theoretically study the problem of binary classification in the presence of random classification noise — the learner, instead of seeing the true labels , sees labels that have independently been flipped with some small probability. Moreover, random label noise is class-conditional — the flip probability depends on the class. We provide… (More)
Composite Objective Mirror Descent
We present a new method for regularized convex optimization and analyze it under both online and stochastic optimization settings. In addition to unifying previously known first-order algorithms, such as the projected gradient method, mirror descent, and forward-backward splitting, our method yields new analysis and algorithms. We also derive specific… (More)
On the Complexity of Linear Prediction: Risk Bounds, Margin Bounds, and Regularization
This work characterizes the generalization ability of algorithms whose predictions are linear in the input vector. To this end, we provide sharp bounds for Rademacher and Gaussian complexities of (constrained) linear classes, which directly lead to a number of generalization bounds. This derivation provides simplified proofs of a number of corollaries… (More)
Stochastic Methods for l1-regularized Loss Minimization
We describe and analyze two stochastic methods for <i>l</i><sub>1</sub> regularized loss minimization problems, such as the Lasso. The first method updates the weight of a single feature at each iteration while the second method updates the entire weight vector but only uses a single training example at each iteration. In both methods, the choice of… (More)
On NDCG Consistency of Listwise Ranking Methods
We study the consistency of listwise ranking methods with respect to the popular Normalized Discounted Cumulative Gain (NDCG) criterion. State of the art listwise approaches replace NDCG with a surrogate loss that is easier to optimize. We characterize NDCG consistency of surrogate losses to discover a surprising fact: several commonly used sur-rogates are… (More)
Efficient bandit algorithms for online multiclass prediction
This paper introduces the Banditron, a variant of the Perceptron [Rosenblatt, 1958], for the multiclass bandit setting. The multiclass bandit setting models a wide range of practical supervised learning applications where the learner only receives partial feedback (referred to as "bandit" feedback, in the spirit of multi-armed bandit models) with respect to… (More)