Hybrid Dynamics in Modelica: Should all Events be Considered Synchronous

The Modelica specification is ambiguous as to whether all the events are synchronous are not. Different interpretations are possible leading to considerable differences in the ways models should be constructed and compilers developed. In this paper we examine this issue and show that there exists an interpretation that is more appropriate than others leading to more efficient compilers. It turns out that this interpretation is not the one currently adopted by Dymola but it is closely related to the Scicos formalism.