Converting Signed Digraphs to Forrester Schematics and Converting Forrester Schematics to Differential Equations

The feasibility of operationalizing the process of translating a signed digraph (or causal diagram) to an associated differential equation model is demonstrated. Starting with the signed digraph the suggested method first classifies all members (quantities and couplings) in the model. The classification step essentially converts the signed digraph to a Forrester schematic. The remaining step consists of converting the Forrester schematic to differential equations. Both steps are described in detail. The classification step consists of a set of rules for identification, whereas the last step utilizes with expediency the notion of dimensional invariance to formulate the equations. It is suggested that the two steps could be partially algorithmatized. Such algorithms would expedite the process of going from signed digraph to equations while simultaneously enabling the policymaker and planner to participate in the formulation process.