Computing differential invariants of hybrid systems as fixedpoints

  • Authors:

  • André Platzer;Edmund M. Clarke

  • Affiliations:

  • Computer Science Department, Carnegie Mellon University, Pittsburgh, USA 15213;Computer Science Department, Carnegie Mellon University, Pittsburgh, USA 15213

  • Venue:
  • Formal Methods in System Design
  • Year:
  • 2009

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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. With this compositional approach we exploit locality in system designs. To improve the verification power, we further introduce a saturation procedure that 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 and car control.