Computing Differential Invariants of Hybrid Systems as Fixedpoints

  • Authors:
  • André Platzer;Edmund M. Clarke

  • Affiliations:
  • Department of Computing Science, University of Oldenburg, Germany;Computer Science Department, Carnegie Mellon University, Pittsburgh

  • Venue:
  • CAV '08 Proceedings of the 20th international conference on Computer Aided Verification
  • Year:
  • 2008

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Abstract

We introduce a fixedpoint algorithm for verifying safety properties of hybrid systems with differential equations whose right-hand sides are polynomials in the state variables. In order to verify nontrivial systems without solving their differential equations and without numerical errors, we use a continuous generalization of induction, for which our algorithm computes the required differential invariants. As a means for combining local differential invariants into global system invariants in a sound way, our fixedpoint algorithm works with a compositional verification logic for hybrid systems. To improve the verification power, we further introduce a saturation procedurethat refines the system dynamics successively with differential invariants until safety becomes provable. By complementing our symbolic verification algorithm with a robust version of numerical falsification, we obtain a fast and sound verification procedure. We verify roundabout maneuvers in air traffic management and collision avoidance in train control.