Abstract
We study verification problems for autonomous swarms of mobile robots that self-organize and cooperate to solve global objectives. In particular, we focus in this paper on the model proposed by Suzuki and Yamashita of anonymous robots evolving in a discrete space with a finite number of locations (here, a ring). A large number of algorithms have been proposed working for rings whose size is not a priori fixed and can be hence considered as a parameter. Handmade correctness proofs of these algorithms have been shown to be error-prone, and recent attention had been given to the application of formal methods to automatically prove those. Our work is the first to study the verification problem of such algorithms in the parameterized case. We show that safety and reachability problems are undecidable for robots evolving asynchronously. On the positive side, we show that safety properties are decidable in the synchronous case, as well as in the asynchronous case for a particular class of algorithms. Several other properties of the protocol can be decided as well. Decision procedures rely on an encoding in Presburger arithmetics formulae that can be verified by an SMT-solver. Feasibility of our approach is demonstrated by the encoding of several case studies.
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This work has been partly supported by the ANR research program ANR FREDDA (ANR-17-CE40-0013).
Appendix: Models for the algorithm with three robots
Appendix: Models for the algorithm with three robots
See Figs. 6, 7, 8, 9, 10 and 11.
Correct model for the algorithm with 3 robots
Buggy model for the algorithm with 3 robots
Model for the algorithm with 6 robots on ring of size 11
Model for the algorithm with 7 robots on ring of size 12 (part I)
Model for the algorithm with 7 robots on ring of size 12 (part II)
Extract of the SMT-LIB code to check the absence of collision in the algorithm with 3 robots
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Sangnier, A., Sznajder, N., Potop-Butucaru, M. et al. Parameterized verification of algorithms for oblivious robots on a ring. Form Methods Syst Des 56, 55–89 (2020). https://doi.org/10.1007/s10703-019-00335-y
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DOI: https://doi.org/10.1007/s10703-019-00335-y