Transferring Causality Analysis from Synchronous Programs to Hybrid Programs

Abstract

Outputs of synchronous programs may suffer from cyclic dependencies since statements are allowed to read the current outputs' values to determine the actions that generate the current values of the outputs. For this reason, compilers have to perform a causality analysis that ensures that at any point of time, there is a unique and constructive way to determine the outputs. The discrete parts of hybrid systems may suffer from the same problem as observed in synchronous programs. As we recently extended our synchronous language Quartz to describe hybrid systems, we explain in this paper how the causality analysis as originally introduced for synchronous systems can also be used to handle cyclic dependencies in hybrid Modelica programs.

Teaching cyber-physical systems

“…solving causality problems, all Quartz programs can be translated to syntactically correct Modelica programs. However, Modelica simulators cannot deal with cyclic dependencies in programs[3].…”