Editing System dynamics (section)

==Application==
System dynamics has found application in a wide range of areas, for example [[Population dynamics|population]], agriculture,<ref>F. H. A. Rahim, N. N. Hawari and N. Z. Abidin, "Supply and demand of rice in Malaysia: A system dynamics approach", International Journal of Supply Chain and Management, Vol.6, No.4, pp. 234-240, 2017.</ref> [[Compartmental models in epidemiology | epidemiological]], [[Ecosystem model|ecological]] and [[Economics|economic]] systems, which usually interact strongly with each other.

System dynamics have various "back of the envelope" management applications. They are a potent tool to:
*Teach [[system thinking]] reflexes to persons being coached
*Analyze and compare assumptions and [[mental model]]s about the way things work
*Gain qualitative insight into the workings of a system or the consequences of a decision
*Recognize archetypes of dysfunctional systems in everyday practice

Computer software is used to [[computer simulation|simulate]] a system dynamics [[model (abstract)|model]] of the situation being studied. Running "what if" simulations to test certain policies on such a model can greatly aid in understanding how the system changes over time.  System dynamics is very similar to [[systems thinking]] and constructs the same [[causal loop diagram]]s of systems with feedback.  However, system dynamics typically goes further and utilises simulation to study the behaviour of systems and the impact of alternative policies.<ref name="SysDynSociety">[http://www.systemdynamics.org/ System Dynamics Society<!-- Bot generated title -->]</ref>

System dynamics has been used to investigate resource dependencies, and resulting problems, in product development.<ref name="Repenning:2001kx">{{cite journal |last=Repenning |first=Nelson P. |year=2001 |title= Understanding fire fighting in new product development |journal= The Journal of Product Innovation Management |volume= 18 |issue=5|pages= 285–300|doi= 10.1016/S0737-6782(01)00099-6|url= https://dspace.mit.edu/bitstream/1721.1/3961/2/Tilting_v40-web.pdf |hdl=1721.1/3961 |hdl-access= free }}</ref><ref name="Repenning:1999ng">Nelson P. Repenning (1999). ''Resource dependence in product development improvement efforts'', [[MIT Sloan School of Management]] Department of Operations Management/System Dynamics Group, Dec 1999.</ref>

A system dynamics approach to  [[macroeconomics]], known as ''[[Minsky (economic simulator)|Minsky]]'',  has been developed by the economist [[Steve Keen]].<ref name="SForge">&nbsp;[http://sourceforge.net/blog/january-2014-potm/&nbsp;SourceForge]&nbsp;Minsky&nbsp;-&nbsp;Project of the month January 2014. Interview with Minsky development team. Accessed January 2014</ref> This has been used to successfully model world economic behaviour from the apparent stability of the [[Great Moderation]] to the [[2008 financial crisis]].

===Example: Growth and decline of companies===
[[Image:Causal Loop Diagram of a Model.png|thumb|600px|center|Causal loop diagram of a model examining the growth or decline of a life insurance company.<ref name ="Tay Feedback"/>]]

The figure above is a causal loop diagram of a system dynamics model created to examine forces that may be responsible for the growth or decline of [[life insurance]] companies in the [[United Kingdom]]. A number of this figure's features are worth mentioning. The first is that the model's negative feedback loops are identified by ''C's'', which stand for ''Counteracting'' loops. The second is that double slashes are used to indicate places where there is a significant delay between causes (i.e., variables at the tails of arrows) and effects (i.e., variables at the heads of arrows). This is a common causal loop diagramming convention in system dynamics. Third, is that thicker lines are used to identify the feedback loops and links that author wishes the audience to focus on. This is also a common system dynamics diagramming convention. Last, it is clear that a decision maker would find it impossible to think through the dynamic behavior inherent in the model, from inspection of the figure alone.<ref name ="Tay Feedback">Michael J. Radzicki and Robert A. Taylor (2008). [http://www.systemdynamics.org/DL-IntroSysDyn/start.htm "Feedback"]. In: ''U.S. Department of Energy's Introduction to System Dynamics''. Retrieved 23 October 2008.</ref>

=== Example: Piston motion ===
# Objective: study of a crank-connecting rod system.<br /> We want to model a crank-connecting rod system through a system dynamic model. Two different full descriptions of the physical system with related systems of equations can be found  [[Piston motion equations#Position|here]] {{in lang|en}} and [[:fr:Système bielle-manivelle#Équations horaires|here]] {{in lang|fr}}; they give the same results. In this example, the crank, with variable radius and angular frequency, will drive a piston with a variable connecting rod length.
# System dynamic modeling: the system is now modeled, according to a stock and flow system dynamic logic.<br /> The figure below shows the stock and flow diagram [[Image:TRUE Piston SFD.png|centre|Stock and flow diagram for crank-connecting rod system|frame]]
# Simulation: the behavior of the crank-connecting rod dynamic system can then be simulated.<br /> The next figure is a 3D simulation created using [[procedural animation]]. Variables of the model animate all parts of this animation: crank, radius, angular frequency, rod length, and piston position.
[[Image:TRUE Procedural Animation.gif|centre|3D [[procedural animation]] of the crank-connecting rod system modeled in 2|frame]]