The ‘Causality’ Quagmire for Formalised Bond Graphs

Bond graphs represent the structure and functionality of mechatronic systems from a power flow perspective. Unfortunately, presentations of bond graphs are replete with ambiguity, significantly impeding understanding. We extend the formalisation in preceding work to address the phenomenon of ‘causality’, intended to help formulate solution strategies for bond graphs, but usually presented in such vague terms that the claims made are easily shown to be false. We show that ‘causality’ only works as advertised in the simplest cases, where it mimics the mathematical definition of bond graph semantics. Counterexamples severely limit the applicability of the notion.