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Sparse-representation-based classification (SRC), which classifies data based on the sparse reconstruction error, has been a new technique in pattern recognition. However, the computation cost for sparse coding is heavy in real applications. In this paper, various dimension reduction methods are studied in the context of SRC to improve classification accuracy as well as reduce computational cost. A feature extraction method, i.e., principal component analysis, and feature selection methods, i.e., Laplacian score and Pearson correlation coefficient, are applied to the data preparation step to preserve the structure of data in the lower-dimensional space. Classification performance of SRC with structure-preserving dimension reduction (SRC-SPDR) is compared to classical classifiers such as k-nearest neighbors and support vector machines. Experimental tests with the UCI and face data sets demonstrate that SRC-SPDR is effective with relatively low computation cost

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Due to the widespread use of mobile devices, it is essential to authenticate users on mobile devices to prevent sensitive information leakage. In this paper, we propose TouchID, which combinedly uses the touch sensor and the inertial sensor for gesture analysis, to provide a touch gesture based user authentication scheme. Specifically, TouchID utilizes the touch sensor to analyze the on-screen gesture while using the inertial sensor to analyze the device's motion caused by the touch gesture, and then combines the unique features from the on-screen gesture and the device's motion for user authentication. To mitigate the intra-class difference and reduce the inter-class similarity, we propose a spatial alignment method for sensor data and segment the touch gesture into multiple sub-gestures in space domain, to keep the stability of the same user and enhance the discriminability of different users. To provide a uniform representation of touch gestures with different topological structures, we present a four-part based feature selection method, which classifies a touch gesture into a start node, an end node, the turning node(s), and the smooth paths, and then select effective features from these parts based on Fisher Score. In addition, considering the uncertainty of user's postures, which may change the sensor data of same touch gesture, we propose a multi-threshold kNN based model to adaptively tolerate the posture difference for user authentication. Finally, we implement TouchID on commercial smartphones and conduct extensive experiments to evaluate TouchID. The experiment results show that TouchID can achieve a good performance for user authentication, i.e., having a low equal error rate of 4.90%.

Emotion-cause pair extraction (ECPE) is a new task which aims at extracting the potential clause pairs of emotions and corresponding causes in a document. To tackle this task, a two-step method was proposed by previous study which first extracted emotion clauses and cause clauses individually, then paired the emotion and cause clauses, and filtered out the pairs without causality. Different from this method that separated the detection and the matching of emotion and cause into two steps, we propose a Symmetric Local Search Network (SLSN) model to perform the detection and matching simultaneously by local search. SLSN consists of two symmetric subnetworks, namely the emotion subnetwork and the cause subnetwork. Each subnetwork is composed of a clause representation learner and a local pair searcher. The local pair searcher is a specially-designed cross-subnetwork component which can extract the local emotion-cause pairs. Experimental results on the ECPE corpus demonstrate the superiority of our SLSN over existing state-of-the-art methods.