Comparing forward and backward reachability as tools for safety analysis

  • Authors:
  • Ian M. Mitchell

  • Affiliations:
  • Department of Computer Science, University of British Columbia, Vancouver, BC, Canada

  • Venue:
  • HSCC'07 Proceedings of the 10th international conference on Hybrid systems: computation and control
  • Year:
  • 2007

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Abstract

Using only the existence and uniqueness of trajectories for a generic dynamic system with inputs, we define and examine eight types of forward and backward reachability constructs. If the input is treated in a worst-case fashion, any forward or backward reach set or tube can be used for safety analysis, but if the input is treated in a best-case fashion only the backward reach tube always provides the correct results. Fortunately, forward and backward algorithms can be exchanged if well-posed reverse time trajectories can be defined. Unfortunately, backward reachability constructs are more likely to suffer from numerical stability issues, especially in systems with significant contraction--the very systems where forward simulation and reachability are most effective.