Some Basic Concepts in System Dynamics - Creative Learning ...

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- 8 - D-4894opposite from the behavior of more complex systems. A person understands fillinga water glass, as in Figure 3. But, if we go to a system that is only five times as!JWF037B"#$%&'()complicated, as in Figure 5, intuition fails. A person cannot look at Figure 5and anticipate the behavior of the pictured system.Figure 5 from World Dynamics is five times more complicated than Figure 4in the sense that it has five stocks—the rectangles in the figure. The figure showshow rapidly apparent complexity increases as more system stocks are added.Mathematicians would describe Figure 5 as a fifth-order, nonlinear, dynamicsystem. No one can predict the behavior by studying the diagram or its underlying
D-4894 - 9 -equations. Only by using computer simulation can the implied behavior berevealed.Figure 5 displays interactions between population, capital equipment,agriculture, resources, and pollution. The diagram links multiple disciplines. Aproper study of systems must usually break down the boundaries betweenacademic disciplines. As stated by Gordon S. Brown, former dean of engineeringat MIT, “The message is in the feedback, and the feedback is inherentlyinterdisciplinary.”3. EVERYONE USES MODELSI sometimes ask an audience how many use models for all their decisions.No one responds. How then, I ask, do they make decisions? They quickly see thatall decisions are made on the basis of mental models. No one’s head contains afamily, city, school, country, or business. Decisions are based only on assumptionsabout separate parts of real systems, and trying by intuition to fit those fragmentsof knowledge into an estimate of how things change and what will be theconsequences of a proposed action.ModelsAll actions based on modelsMental modelsBasis of human activity.Major strength:Tremendous store ofinformationMajor weakness:Unreliable in handlingcomplexity and dynamicchange.JWF12Figure 63.1. Computer Models andMental ModelsSystem dynamics builds two-waycommunication between mental modelsand simulation models. Mental modelsare the basis for everyday decisions.Mental models contain tremendousstores of information. But the humanmind is unreliable in understanding whatthe available information means in termsof behavior. Computer simulationmeshes nicely with mental models bytaking the mentally stored informationand then displaying the dynamicconsequences.Such mental models belong to the same class as the computer models usedin system dynamics. In fact a system dynamics model is often built fromassumptions in the mental models. Mental models are rich and often sufficiently
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Some Basic Concepts in System Dynamics - Creative Learning ...

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