Machine translation is a popular test bed for research in neural sequence-to-sequence models but despite much recent research, there is still a lack of understanding of these models. Practitioners report performance degradation with large beams, the under-estimation of rare words and a lack of diversity in the final translations. Our study relates some of these issues to the inherent uncertainty of the task, due to the existence of multiple valid translations for a single source sentence, and to the extrinsic uncertainty caused by noisy training data. We propose tools and metrics to assess how uncertainty in the data is captured by the model distribution and how it affects search strategies that generate translations. Our results show that search works remarkably well but that the models tend to spread too much probability mass over the hypothesis space. Next, we propose tools to assess model calibration and show how to easily fix some shortcomings of current models. We release both code and multiple human reference translations for two popular benchmarks.

本研究提出了工具和度量方法来评估机器翻译模型中数据不确定性的捕捉，以及这种不确定性如何影响生成翻译的搜索策略。我们的结果表明，搜索功能表现出色，但模型往往在假设空间中分散了太多的概率质量。此外，我们还提出了评估模型校准的工具，并展示了如何轻松解决当前模型的一些缺陷。

神经机器翻译中的不确定性分析