Abstract

It is often informally stated that system dynamics (SD) models are equivalent to differential equation systems. This paper formalizes the concept of an SD model as a collection of rate equations, auxiliary equations, and the 'flow coupling' of flows to stocks. If such a model has no causal loops that consist only of auxiliaries, then it is possible to find an equivalent differential equation system. The generalized solution concept of Carathéodory is shown to be suitable for defining the corresponding state transition map, which leads to a formal dynamical system.