Imbalanced classification is a challenging task in the fields of machine learning, data mining and pattern recognition. Cost-sensitive online algorithms are very important methods for large-scale imbalanced classification problems. At present, most of the cost-sensitive classification algorithms focus on the accuracy of the minority class and ignore the accuracy of the majority class. In order to better balance the accuracy between the minority class and the majority class, in this article, a misclassification cost is presented to ensure that the cost-sensitive online algorithm can better deal with the imbalanced classification problems without signifificantly reducing the accuracy of the majority class. Based on the proposed misclassification cost, a novel cost-sensitive online adaptive kernel learning algorithm is proposed to boost the adaptability of kernel function when data arrives one by one. According to the essential characteristics of the imbalanced binary classification, a cost-sensitive online adaptive kernel learning algorithm is given to handle the large-scale imbalanced multi-class classification problems. Theoretical analysis of the proposed algorithms are provided. Extensive experiments demonstrate that compared with the state-of-the-art imbalanced classification algorithms, the proposed algorithms can significantly improve the classification performances on most of the large-scale imbalanced data sets.

Domain adaptation is concerned with the problem of generalizing a classification model to a target domain with little or no labeled data, by leveraging the abundant labeled data from a related source domain. The source and target domains possess different joint probability distributions, making it challenging for model generalization. In this article, we introduce domain neural adaptation (DNA): an approach that exploits nonlinear deep neural network to 1) match the source and target joint distributions in the network activation space and 2) learn the classifier in an end-to-end manner. Specifically, we employ the relative chi-square divergence to compare the two joint distributions, and show that the divergence can be estimated via seeking the maximal value of a quadratic functional over the reproducing kernel hilbert space. The analytic solution to this maximization problem enables us to explicitly express the divergence estimate as a function of the neural network mapping. We optimize the network parameters to minimize the estimated joint distribution divergence and the classification loss, yielding a classification model that generalizes well to the target domain. Empirical results on several visual datasets demonstrate that our solution is statistically better than its competitors.