Symbolic Simulation of Hybrid Systems

Continuous action systems (CAS) is a formalism intended for modeling hybrid systems (systems that combine discrete control with continuous behavior), and proving properties about the model within refinement calculus. In this paper we use a symbolic manipulation program to build a tool for simulating CAS models by calculating symbolically the time evolution of the discrete and continuous CAS model functions, as explicit and exact expressions of a continuous time variable. We may then study the time behavior and general properties of the model by plotting these functions with respect to time. For certain models our tool eliminates the need for introducing tolerances into the model structure. The tool is useful for checking that the model behaves correctly, and we can sometimes study the behavior of CAS models with in principle infinite precision.