Sentiment analysis has attracted extensive attention in recent years. Existing work mainly focuses on sentiment classification task in which a text or sentence usually contains sentiment word to express subjective feeling. However, little research is proposed for identifying implicit polarity of a text. Here, implicit polarity of a text means that the text does not contain sentiment words but still express a positive or negative sentiment. To address this issue, we propose an attention-based neural network model to identify implicit polarity of events. In particular, the model first learns the sentence representation by recurrent neural network with gated recurrent unit. Then multiple hops attention mechanism is used for capturing multiple aspects closely related to sentiment polarity and the event type. Experimental results on SemEval 2015 dataset show the effectiveness of the proposed model, outperforming the previous systems and strong neural baselines.

Financial sentiment analysis is a fine-grained sentiment analysis task that needs to predict the sentiment value toward a given target entity. Recently, dependency-based graph neural networks have been introduced for target-based sentiment analysis. However, financial sentiment analysis with implicit sentiment expression is more challenging than target-based explicit sentiment analysis, requiring a deep understanding of the complex association between the sentiment clue in context and the target entity. In previous work related to financial sentiment analysis, most methods focused on learning the simple word-to-word relations between the contextual words and the target entity based on the dependency tree of the sentence, ignoring the exploitation of span-boundary information and phrase-level syntactic knowledge with regard to the target entity. In this paper, we perform financial implicit sentiment analysis by taking phrases as basic semantic units and proposing a graph attention network ( $PhraseGAT$ ) based on the constituent tree to leverage the phrase syntactic knowledge. To enhance the information flow between the nodes in the graph, we construct a heterogeneous graph based on the constituent tree and encode higher-order neighbor information. In addition, we introduce a multi-edge-type graph attention network ( $MET$ - $GAT$ ) to take full consideration of syntax and semantic interactions for the final prediction on the sentiment value of the target entity. Our proposed approach achieves 85.56% and 84.37% cosine similarity on public benchmark HEADLINE and MICROBLOG datasets, outperforms several strong baselines and achieves new state-of-the-art performance, verifying its effectiveness.

Implicit sentiment analysis is a challenging task because the sentiment of a text is expressed in a connotative manner. To tackle this problem, we propose to use textual events as a knowledge source to enrich network representations. To consider task interactions, we present a novel lightweight joint learning paradigm that can pass task-related messages between tasks during training iterations. This is distinct from previous methods that involve multi-task learning by simple parameter sharing. Besides, a human-annotated corpus with implicit sentiment labels and event labels is scarce, which hinders practical applications of deep neural models. Therefore, we further investigate a back-translation approach to expand training instances. Experiment results on a public benchmark demonstrate the effectiveness of both the proposed multi-task architecture and data augmentation strategy.

High-dimensional small-sample data are widely encountered in medical diagnosis, bioinformatics, and industrial inspection, where traditional feature selection methods often suffer from premature convergence and local optima. To address these issues, this paper proposes a Hybrid Breeding-based Co-evolutionary Ant Colony Optimization method (HBACO) for feature selection. Inspired by the principle of hybrid breeding, in which individuals with distinct traits produce superior offspring through cross recombination, inheritance of desirable genes and continuous evolution, the proposed algorithm establishes a three-population collaborative framework. It consists of an ACO-based search population, an HRO-based evolutionary population and a cooperative feedback population that evolve iteratively together. Furthermore, we devise a heuristic strategy integrating correlation and genetic characteristics to help mine high-value feature subsets. Meanwhile, a collaborative pheromone updating mechanism is adopted to realize efficient knowledge sharing among populations. Experiments conducted on 13 high-dimensional datasets, including Colon and Lung, demonstrate that HBACO achieves superior classification accuracy, feature reduction performance, and convergence behavior compared with 10 representative algorithms. Specifically, HBACO improves the average classification accuracy by 3.9% and achieves an average feature dimensionality reduction rate of 91.4%. Statistical tests further confirm the significance of the proposed method. The results indicate that HBACO provides an effective and robust solution for high-dimensional feature selection problems.