Neural machine translation is a relatively new approach to statistical
machine translation based purely on neural networks. The neural machine
translation models often consist of an encoder and a decoder. The encoder
extracts a fixed-length representation from a variable-length input sentence,
and the decoder generates a correct translation from this representation. In
this paper, we focus on analyzing the properties of the neural machine
translation using two models; RNN Encoder--Decoder and a newly proposed gated
recursive convolutional neural network. We show that the neural machine
translation performs relatively well on short sentences without unknown words,
but its performance degrades rapidly as the length of the sentence and the
number of unknown words increase. Furthermore, we find that the proposed gated
recursive convolutional network learns a grammatical structure of a sentence
automatically.

分析神经机器翻译的性能，研究了两种模型：RNN 编码器 - 解码器和新提出的门控递归卷积神经网络，结果显示神经机器翻译在翻译较短，不含生词句子时表现相对良好，但随着句子长度和生词数的增加，其性能会迅速降低。同时发现，所提出的门控递归卷积网络能够自动学习句子的语法结构。