Countless learning tasks require awareness of time. Image captioning, speech synthesis, and video game playing all require that a model generate sequences of outputs. In other domains, such as time series prediction, video analysis, and music information retrieval, a model must learn from sequences of inputs. Significantly more interactive tasks, such as natural language translation, engaging in dialogue, and robotic control, often demand both. Recurrent neural networks (RNNs) are a powerful family of connectionist models that capture time dynamics via cycles in the graph. Unlike feedforward neural networks, recurrent networks can process examples one at a time, retaining a state, or memory, that reflects an arbitrarily long context window. While these networks have long been difficult to train and often contain millions of parameters, recent advances in network architectures, optimization techniques, and parallel computation have enabled large-scale learning with recurrent nets. Over the past few years, systems based on state of the art long short-term memory (LSTM) and bidirectional recurrent neural network (BRNN) architectures have demonstrated record-setting performance on tasks as varied as image captioning, language translation, and handwriting recognition. In this review of the literature we synthesize the body of research that over the past three decades has yielded and reduced to practice these powerful models. When appropriate, we reconcile conflicting notation and nomenclature. Our goal is to provide a mostly self-contained explication of state of the art systems, together with a historical perspective and ample references to the primary research.

本文对于近三十年来产生和实践了重要的循环神经网络（RNN），LSTM和BRNN等模型的研究进行综述，旨在提供一个自成体系的最前沿阐述和历史视角，并引用了相关研究文献。

循环神经网络在序列学习中的关键评估