Reachability in Simple Neural Networks

Issue title: 14th and 15th International Conferences on Reachability Problems

Guest editors: Paul C. Bell, Igor Potapov, Sylvain Schmitz and Patrick Totzke

Article type: Research Article

Authors: Sälzer, Marco^{; *} | Lange, Martin

Affiliations: School of Electr. Eng. and Computer Science, University of Kassel, Germany. marco.saelzer@uni-kassel.de, martin.lange@uni-kassel.de

Correspondence: [*] Address for correspondence: School of Electr. Eng. and Computer Science, University of Kassel, Germany

Abstract: We investigate the complexity of the reachability problem for (deep) neural networks: does it compute valid output given some valid input? It was recently claimed that the problem is NP-complete for general neural networks and specifications over the input/output dimension given by conjunctions of linear inequalities. We recapitulate the proof and repair some flaws in the original upper and lower bound proofs. Motivated by the general result, we show that NP-hardness already holds for restricted classes of simple specifications and neural networks. Allowing for a single hidden layer and an output dimension of one as well as neural networks with just one negative, zero and one positive weight or bias is sufficient to ensure NP-hardness. Additionally, we give a thorough discussion and outlook of possible extensions for this direction of research on neural network verification.

Keywords: machine learning, computational complexity, formal specification and verification

DOI: 10.3233/FI-222160

Journal: Fundamenta Informaticae, vol. 189, no. 3-4, pp. 241-259, 2022