Chun Gan


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Probabilistic Graph Reasoning for Natural Proof Generation
Changzhi Sun | Xinbo Zhang | Jiangjie Chen | Chun Gan | Yuanbin Wu | Jiaze Chen | Hao Zhou | Lei Li
Findings of the Association for Computational Linguistics: ACL-IJCNLP 2021

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Vocabulary Learning via Optimal Transport for Neural Machine Translation
Jingjing Xu | Hao Zhou | Chun Gan | Zaixiang Zheng | Lei Li
Proceedings of the 59th Annual Meeting of the Association for Computational Linguistics and the 11th International Joint Conference on Natural Language Processing (Volume 1: Long Papers)

The choice of token vocabulary affects the performance of machine translation. This paper aims to figure out what is a good vocabulary and whether we can find the optimal vocabulary without trial training. To answer these questions, we first provide an alternative understanding of vocabulary from the perspective of information theory. It motivates us to formulate the quest of vocabularization – finding the best token dictionary with a proper size – as an optimal transport (OT) problem. We propose VOLT, a simple and efficient solution without trial training. Empirical results show that VOLT beats widely-used vocabularies in diverse scenarios, including WMT-14 English-German translation, TED bilingual translation, and TED multilingual translation. For example, VOLT achieves 70% vocabulary size reduction and 0.5 BLEU gain on English-German translation. Also, compared to BPE-search, VOLT reduces the search time from 384 GPU hours to 30 GPU hours on English-German translation. Codes are available at