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
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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