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System Dynamics
System dynamics is an approach to modeling systems
(particularly social systems) that emphasizes their feedback loops, using stocks, auxiliary variables,
and flows of influence. Invented by Professor Jay Forrester
of MIT in the late 1950s, system dynamics uses a standard
visual notation and an interrelated collection of mathematical
equations to mimic a system's important structure,
with the goal of gaining new insights into how and why the
system works the way it does. A computer program then runs
the equations, which simulates the behavior of the system.
The chief output is in the form of graphs over time, which
show the dynamic behavior of the system under the assumptions
used for each particular simulation run.
This is such a simple and close approximation of reality that
system dynamics modeling has achieved great success in a number
of difficult problem areas, including business management, the
American urban decay problem of the 1960s, epidemiology, ecology,
and environmental sustainability. It's most famous application
was the Limits
to Growth project in 1972. (Also see this short review
of the Limits to Growth project, written by Dennis Meadows in 2004.)
Further Reading
 For a ten minute introduction to how system dynamics modeling is done, watch the How Simulation Models Work video.
For a discussion of why system dynamics is so important, see Structure.
For an example of how system dynamics is the key tool
in an appropriate problem solving process, please see the Dueling
Loops paper. This will introduce you to simple feedback loops,
and then progressively more complex abstractions that are easily
handled by the powerful tool of system dynamics.
For an exciting
tale by Jay Forrester himself on how he applied system dynamics
to the urban decay problem, see chapter one in the manuscript to Analytical
Activism. Or you can read the original longer story the material
in chapter one is from, at The
Beginning of System Dynamics PDF , which
is a 16 page PDF file.
For a fascinating look at where system dynamics might be going, see Jay Forrester's talk on Designing the Future, given in 1998.
For more see the wikipedia
entry for System Dynamics.
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