Robust Semi-Supervised Learning with Out of Distribution Data

Recent Semi-supervised learning (SSL) works show significant improvement in SSL algorithms' performance using better-unlabeled data representations. However, recent work [Oliver et al., 2018] shows that the SSL algorithm's performance could degrade when the unlabeled set has out-of-distribution examples (OODs). In this work, we first study the critical causes of OOD's negative impact on SSL algorithms. We found that (1) the OOD's effect on the SSL algorithm's performance increases as its distance to the decision boundary decreases, and (2) Batch Normalization (BN), a popular module, could degrade the performance instead of improving the performance when the unlabeled set contains OODs. To address the above causes, we proposed a novel unified-robust SSL approach that can be easily extended to many existing SSL algorithms, and improve their robustness against OODs. In particular, we propose a simple modification of batch normalization, called weighted batch normalization, that improves BN's robustness against OODs. We also developed two efficient hyper-parameter optimization algorithms that have different tradeoffs in computational efficiency and accuracy. Extensive experiments on synthetic and real-world datasets prove that our proposed approaches significantly improves the robustness of four representative SSL algorithms against OODs compared with four state-of-the-art robust SSL approaches.Comment: Preprin

Implicit Filter Sparsification In Convolutional Neural Networks

We show implicit filter level sparsity manifests in convolutional neural networks (CNNs) which employ Batch Normalization and ReLU activation, and are trained with adaptive gradient descent techniques and L2 regularization or weight decay. Through an extensive empirical study (Mehta et al., 2019) we hypothesize the mechanism behind the sparsification process, and find surprising links to certain filter sparsification heuristics proposed in literature. Emergence of, and the subsequent pruning of selective features is observed to be one of the contributing mechanisms, leading to feature sparsity at par or better than certain explicit sparsification / pruning approaches. In this workshop article we summarize our findings, and point out corollaries of selective-featurepenalization which could also be employed as heuristics for filter pruningComment: ODML-CDNNR 2019 (ICML'19 workshop) extended abstract of the CVPR 2019 paper "On Implicit Filter Level Sparsity in Convolutional Neural Networks, Mehta et al." (arXiv:1811.12495

A Batch Noise Contrastive Estimation Approach for Training Large Vocabulary Language Models

Training large vocabulary Neural Network Language Models (NNLMs) is a difficult task due to the explicit requirement of the output layer normalization, which typically involves the evaluation of the full softmax function over the complete vocabulary. This paper proposes a Batch Noise Contrastive Estimation (B-NCE) approach to alleviate this problem. This is achieved by reducing the vocabulary, at each time step, to the target words in the batch and then replacing the softmax by the noise contrastive estimation approach, where these words play the role of targets and noise samples at the same time. In doing so, the proposed approach can be fully formulated and implemented using optimal dense matrix operations. Applying B-NCE to train different NNLMs on the Large Text Compression Benchmark (LTCB) and the One Billion Word Benchmark (OBWB) shows a significant reduction of the training time with no noticeable degradation of the models performance. This paper also presents a new baseline comparative study of different standard NNLMs on the large OBWB on a single Titan-X GPU.Comment: Accepted for publication at INTERSPEECH'1