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Towards Denotational Semantics of AD for Higher-Order, Recursive, Probabilistic Languages
Alexander Lew · Mathieu Huot · Vikash Mansinghka

Mon Dec 13 12:00 PM -- 12:15 PM (PST) @
Event URL: https://openreview.net/forum?id=nNv6SGFIUyp »

Automatic differentiation (AD) aims to compute derivatives of user-defined functions, but in Turing-complete languages, this simple specification does not fully capture AD’s behavior: AD sometimes disagrees with the true derivative of a differentiable program, and when AD is applied to non-differentiable or effectful programs, it is unclear what guarantees (if any) hold of the resulting code. We study an expressive differentiable programming language, with piecewise-analytic primitives, higher-order functions, and general recursion. Our main result is that even in this general setting, a version of Lee et al. [2020]’s correctness theorem (originally proven for a first-order language without partiality or recursion) holds: all programs denote so-called ωPAP functions, and AD computes correct intensional derivatives of them. Mazza and Pagani [2021]’s recent theorem, that AD disagrees with the true derivative of a differentiable recursive program at a measure-zero set of inputs, can be derived as a straight-forward corollary of this fact. We also apply the framework to study probabilistic programs, and recover a recent result from Mak et al. [2021] via a novel denotational argument.

Author Information

Alexander Lew (MIT)
Mathieu Huot (Department of Computer Science, University of Oxford)
Vikash Mansinghka (Massachusetts Institute of Technology)

Vikash Mansinghka is a research scientist at MIT, where he leads the Probabilistic Computing Project. Vikash holds S.B. degrees in Mathematics and in Computer Science from MIT, as well as an M.Eng. in Computer Science and a PhD in Computation. He also held graduate fellowships from the National Science Foundation and MIT’s Lincoln Laboratory. His PhD dissertation on natively probabilistic computation won the MIT George M. Sprowls dissertation award in computer science, and his research on the Picture probabilistic programming language won an award at CVPR. He served on DARPA’s Information Science and Technology advisory board from 2010-2012, and currently serves on the editorial boards for the Journal of Machine Learning Research and the journal Statistics and Computation. He was an advisor to Google DeepMind and has co-founded two AI-related startups, one acquired and one currently operational.

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