Theano: A Python framework for fast computation of mathematical expressions

Theanois a Python library that allows to define, optimize, and evaluate mathematical expressions involving multi-dimensional arrays efficiently. Since its introduction, it has been one of the most used CPU and GPU mathematical compilers - especially in the machine learningcommunity - and has shown steady performance improvements. Theanois being actively and continuously developed since 2008, multiple frameworks have been built on top of it and it has been used to produce many state-of-the-art machine learningmodels. The present article is structured as follows. Section I provides an overview of the Theanosoftware and its community. Section II presents the principal features of Theanoand how to use them, and compares them with other similar projects. Section III focuses on recently-introduced functionalities and improvements. Section IV compares the performance of Theanoagainst Torch7 and TensorFlow on several machine learningmodels. Section V discusses current limitations of Theanoand potential ways of improving it.