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Machine translation is shifting to an end-to-end approach based on deep neural networks. The state of the art achieves impressive results for popular language pairs such as English -French or English -Chinese. However for English -Vietnamese the shortage of parallel corpora and expensive hyper-parameter search present practical challenges to neural-based approaches. This paper highlights our efforts on improving English-Vietnamese translations in two directions: (1) Building the largest open Vietnamese -English corpus to date, and (2) Extensive experiments with the latest neural models to achieve the highest BLEU scores. Our experiments provide practical examples of effectively employing different neural machine translation models with low-resource language pairs. IntroductionMachine translation is shifting to an end-to-end approach based on deep neural networks. Recent studies in neural machine translation (NMT) such as [41,2,42,14] have produced impressive advancements over phrase-based systems while eliminating the need for handengineered features. Most NMT systems are based on the encoder-decoder architecture which consists of two neural networks. The encoder compresses the source sequences into a real-valued vector, which is consumed by the decoder to generate the target sequences. The process is done in an end-to-end fashion, demonstrated the capability of learning representation directly from the training data.The typical sequence-to-sequence machine translation model consists of two recurrent neural networks (RNNs) and an attention mechanism [2,26]. Despite great improvements over traditional models [42,35,27] this architecture has certain shortcomings, namely that the recurrent networks are not easily parallelized and limited gradient flow while training deep models.Recent designs such as ConvS2S [14] and Transformer [41] can be better parallelized while producing better results on WMT datasets. However, NMT models take a long time to train and include many hyper-parameters. There is a number of works that tackle the problem of hyper-parameter selection [5,33] but they mostly focus on high-resource language pairs data, thus their findings may not translate well to low-resource translation tasks such as English-Vietnamese. Unlike in Computer Vision [17,20], the task of adapting parameters spaces from one NMT model to other NMT models is nearly impossible [5]. This reason limits researchers and engineers to reach good-chose hyper-parameters and well-trained models.

Many optimization problems such as Maximum Independent Set, Maximum Clique, Minimum Clique Cover and Maximum Induced Matching are NP-hard on general graphs. However, they could be solved in polynomial time when restricted to some particular graph classes such as comparability and co-comparability graph classes. In this paper, we summarize the latest algorithms solving some classical NP-hard problems on some graph classes over the years. Moreover, we apply the -redundant technique to obtain linear time O(j j) algorithms which find a Maximum Induced Matching on interval and circular-arc graphs. Inspired of these results, we have proposed some competitive programming problems for some programming contests in Vietnam in recent years.

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