Yong Zhuang

A fast parallel SGD for matrix factorization in shared memory systems

Matrix factorization is known to be an effective method for recommender systems that are given only the ratings from users to items. Currently, stochastic gradient descent (SGD) is one of the most popular algorithms for matrix factorization. However, as a sequential approach, SGD is difficult to be parallelized for handling web-scale problems. In this paper, we develop a fast parallel SGD method, FPSGD, for shared memory systems. By dramatically reducing the cache-miss rate and carefully addressing the load balance of threads, FPSGD is more efficient than state-of-the-art parallel algorithms for matrix factorization.

Field-aware Factorization Machines for CTR Prediction

Click-through rate (CTR) prediction plays an important role in computational advertising. Models based on degree-2 polynomial mappings and factorization machines (FMs) are widely used for this task. Recently, a variant of FMs, field-aware factorization machines (FFMs), outperforms existing models in some world-wide CTR-prediction competitions. Based on our experiences in winning two of them, in this paper we establish FFMs as an effective method for classifying large sparse data including those from CTR prediction. First, we propose efficient implementations for training FFMs. Then we comprehensively analyze FFMs and compare this approach with competing models. Experiments show that FFMs are very useful for certain classification problems. Finally, we have released a package of FFMs for public use.

A Fast Parallel Stochastic Gradient Method for Matrix Factorization in Shared Memory Systems

Matrix factorization is known to be an effective method for recommender systems that are given only the ratings from users to items. Currently, stochastic gradient (SG) method is one of the most popular algorithms for matrix factorization. However, as a sequential approach, SG is difficult to be parallelized for handling web-scale problems. In this article, we develop a fast parallel SG method, FPSG, for shared memory systems. By dramatically reducing the cache-miss rate and carefully addressing the load balance of threads, FPSG is more efficient than state-of-the-art parallel algorithms for matrix factorization.

A Learning-Rate Schedule for Stochastic Gradient Methods to Matrix Factorization

Stochastic gradient methods are effective to solve matrix factorization problems. However, it is well known that the performance of stochastic gradient method highly depends on the learning rate schedule used; a good schedule can significantly boost the training process. In this paper, motivated from past works on convex optimization which assign a learning rate for each variable, we propose a new schedule for matrix factorization. The experiments demonstrate that the proposed schedule leads to faster convergence than existing ones. Our schedule uses the same parameter on all data sets included in our experiments; that is, the time spent on learning rate selection can be significantly reduced. By applying this schedule to a state-of-the-art matrix factorization package, the resulting implementation outperforms available parallel matrix factorization packages.

Distributed Newton Methods for Regularized Logistic Regression

Regularized logistic regression is a very useful classification method, but for large-scale data, its distributed training has not been investigated much. In this work, we propose a distributed Newton method for training logistic regression. Many interesting techniques are discussed for reducing the communication cost and speeding up the computation. Experiments show that the proposed method is competitive with or even faster than state-of-the-art approaches such as Alternating Direction Method of Multipliers (ADMM) and Vowpal Wabbit (VW). We have released an MPI-based implementation for public use.

Combination of feature engineering and ranking models for paper-author identification in KDD Cup 2013

The track 1 problem in KDD Cup 2013 is to discriminate between papers confirmed by the given authors from the other deleted papers. This paper describes the winning solution of team National Taiwan University for track 1 of KDD Cup 2013. First, we conduct the feature engineering to transform the various provided text information into 97 features. Second, we train classification and ranking models using these features. Last, we combine our individual models to boost the performance by using results on the internal validation set and the official Valid set. Some effective post-processing techniques have also been proposed. Our solution achieves 0.98259 MAP score and ranks the first place on the private leaderboard of Test set.

Naive Parallelization of Coordinate Descent Methods and an Application on Multi-core L1-regularized Classification

It is well known that a direct parallelization of sequential optimization methods (e.g., coordinate descent and stochastic gradient methods) is often not effective. The reason is that at each iteration, the number of operations may be too small. We point out that this common understanding may not be true if the algorithm sequentially accesses the data in a feature-wise manner. For almost all real-world sparse sets we have examined, some features are much denser than others. Thus a direct parallelization of loops in a sequential method may result in excellent speedup. This approach possesses an advantage of retaining all convergence results because the algorithm is not changed at all. We apply this idea on coordinate descent (CD) methods, which are effective single-thread technique for L1-regularized classification. Further, an investigation on the shrinking technique commonly used to remove some features in the training process shows that this technique helps the parallelization of CD methods. Experiments indicate that a naive parallelization achieves better speedup than existing methods that laboriously modify the algorithm to achieve parallelism. Though a bit ironic, we conclude that the naive parallelization of the CD method is a highly competitive and robust multi-core implementation for L1-regularized classification.