System Dynamics Pitfalls and Pointers

Integration and Differentiation

In system dynamics modelling we are primarily interested in accumulations in our models. Accumulations (or stocks) are state variables, expressed in <> and represent mathematical integration with respect to time. Rate variables (or flows) control flows, and cause accumulations to change with respect to time: flows are expressed as flow in <>. In our models, stocks and flows can be linked by either physical flows or information flows. The structural linkage results either in mathematical integration (summation or accumulation) or mathematical differentiation (an indication of rate of change of a variable).
     The following is designed to explain how to define system dynamics structure and link stocks and flows together in ways which correctly enable simulation of mathematical integration or mathematical differentiation .

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