Relevance ranking models based on additive ensembles of regression trees have shown quite good effectiveness in web search engines. In the era of big data, tree ensemble models grow large in both tree depth and ensemble size to provide even better search relevance and user experience. However, the computational cost for their scoring process is high, such that it becomes a challenging issue to apply the big tree ensemble models in a search engine which needs to answer thousands of queries per second. Although several works have been proposed to improve the scoring process, the challenge is still great especially when the model size grows large. In this paper, we present RapidScorer , a novel framework for speeding up the scoring process of industry-scale tree ensemble models, without hurting the quality of scoring results. RapidScorer introduces a modified run length encoding called epitome to the bitvector representation of the tree nodes. Epitome can greatly reduce the computation cost to traverse the tree ensemble, and work with several other proposed strategies to maximize the compactness of data units in memory. The achieved compactness makes it possible to fully utilize data parallelization to improve model scalability. Experiments on two web search benchmarks show that, RapidScorer achieves significant speed-up over the state-of-the-art methods: V-QuickScorer , ranging from 1.3x to 3.5x; QuickScorer , ranging from 2.1x to 25.0x; VPred , ranging from 2.3x to 18.3x; and XGBoost , ranging from 2.6x to 42.5x.

We introduce bilingual word embeddings: semantic embeddings associated across two languages in the context of neural language models.We propose a method to learn bilingual embeddings from a large unlabeled corpus, while utilizing MT word alignments to constrain translational equivalence.The new embeddings significantly out-perform baselines in word semantic similarity.A single semantic similarity feature induced with bilingual embeddings adds near half a BLEU point to the results of NIST08 Chinese-English machine translation task.

We apply salient feature detection and tracking in videos to simulate fixations and smooth pursuit in human vision. With tracked sequences as input, a hierarchical network of modules learns invariant features using a temporal slowness constraint. The network encodes invariance which are increasingly complex with hierarchy. Although learned from videos, our features are spatial instead of spatial-temporal, and well suited for extracting features from still images. We applied our features to four datasets (COIL-100, Caltech 101, STL-10, PubFig), and observe a consistent improvement of 4% to 5% in classification accuracy. With this approach, we achieve state-of-the-art recognition accuracy 61% on STL-10 dataset.

Previous work on action recognition has focused on adapting hand-designed local features, such as SIFT or HOG, from static images to the video domain. In this paper, we propose using unsupervised feature learning as a way to learn features directly from video data. More specifically, we present an extension of the Independent Subspace Analysis algorithm to learn invariant spatio-temporal features from unlabeled video data. We discovered that, despite its simplicity, this method performs surprisingly well when combined with deep learning techniques such as stacking and convolution to learn hierarchical representations. By replacing hand-designed features with our learned features, we achieve classification results superior to all previous published results on the Hollywood2, UCF, KTH and YouTube action recognition datasets. On the challenging Hollywood2 and YouTube action datasets we obtain 53.3% and 75.8% respectively, which are approximately 5% better than the current best published results. Further benefits of this method, such as the ease of training and the efficiency of training and prediction, will also be discussed. You can download our code and learned spatio-temporal features here: http://ai.stanford.edu/~wzou/.