LSTM: A Search Space Odyssey

Klaus Greff, Rupesh K. Srivastava, Jan Koutnik, Bas R. Steunebrink, Jurgen Schmidhuber

Research output: Contribution to journalArticlepeer-review

4114 Scopus citations


Several variants of the long short-term memory (LSTM) architecture for recurrent neural networks have been proposed since its inception in 1995. In recent years, these networks have become the state-of-the-art models for a variety of machine learning problems. This has led to a renewed interest in understanding the role and utility of various computational components of typical LSTM variants. In this paper, we present the first large-scale analysis of eight LSTM variants on three representative tasks: Speech recognition, handwriting recognition, and polyphonic music modeling. The hyperparameters of all LSTM variants for each task were optimized separately using random search, and their importance was assessed using the powerful functional ANalysis Of VAriance framework. In total, we summarize the results of 5400 experimental runs ≈15 years of CPU time), which makes our study the largest of its kind on LSTM networks. Our results show that none of the variants can improve upon the standard LSTM architecture significantly, and demonstrate the forget gate and the output activation function to be its most critical components. We further observe that the studied hyperparameters are virtually independent and derive guidelines for their efficient adjustment.
Original languageEnglish (US)
Pages (from-to)2222-2232
Number of pages11
JournalIEEE Transactions on Neural Networks and Learning Systems
Issue number10
StatePublished - Oct 1 2017
Externally publishedYes


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