System dynamics diagrams

• A graphical modeling method:
  • used mainly in non-technical areas like economics or ecology
  • well known application: world models (Forrester, Meadows)
  • concentrates on basic variables - hides concrete mathematical relations
  • "water flow" paradigm with basic components:
    • 
    • reservoirs = state variables
    • flows = changes in time (derivatives)
    • converters = auxiliary variables (and their formulas)
• Implementations:
  • Stella (isee systems)
  • Vensym (Ventana systems), Simile (Simulistics), ...
  • Modelica library from Cellier et al.
• Causality:
  • designation of all connections as inputs or outputs
  • fixed for implementation in Simulink
  • dynamic in Physical Modeling (Modelica)
  • seems to be trivial here - but isn't!