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Multitask feature selection (MTFS) methods have become more important for many real world applications, especially in a high-dimensional setting. The most widely used assumption is that all tasks share the same features, and the $l_{2,1}$ regularization method is usually applied. However, this assumption may not hold when the correlations among tasks are not obvious. Learning with unrelated tasks together may result in negative transfer and degrade the performance. In this paper, we present a flexible MTFS by graph-clustered feature sharing approach. To avoid the above limitation, we adopt a graph to represent the relevance among tasks instead of adopting a hard task set partition. Furthermore, we propose a graph-guided regularization approach such that the sparsity of the solution can be achieved on both the task level and the feature level, and a variant of the smooth proximal gradient method is developed to solve the corresponding optimization problem. An evaluation of the proposed method on multitask regression and multitask binary classification problem has been performed. Extensive experiments on synthetic datasets and real-world datasets demonstrate the effectiveness of the proposed approach to capture task structure. [ABSTRACT FROM AUTHOR]

In this paper, we propose a novel corpus-based enrichment approach for short text clustering. Since sparseness brings about the problem of insufficient word co-occurrence and lack of context information, previous researches use external sources such as Wikipedia or WordNet to enrich the representation of short text documents, which requires extra resources and might lead to possible inconsistency. On the other hand, corpus-based approaches use no external information in mining short text data. By introducing a set of conjugate definitions to characterize the structures of topics and words, and by proposing a virtual generative procedure for short texts, we perform expansion on short text data. Specifically, new words which may not appear in a short text document were added with a virtual term frequency, and this virtual frequency is obtained from the posterior probabilities of new words given all the words in that document. The complete procedure can be regarded as mapping data points (documents) from the original feature space to a hidden semantic space (topic space). After performing semantic smoothing, data points are then mapped back to the original space. We conduct experiments on two short text datasets, and the results show that the proposed method can effectively address the sparseness problem. For these datasets, our method, using only a basic clustering algorithm, attains a comparable performance with methods based on enrichment with external information sources. [ABSTRACT FROM AUTHOR]