System Dynamics Applications

System Dynamics Pitfalls and Pointers


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Basic Model Building—Modules and Constructor Diagrams.  Step-by-step model-building is described by McLucas (2005). Further explanation of intervening steps is provided to make model building even easier.

Assuring Integrity of Units Used In Models.  The following explains how to assure the integrity of units used in system dynamics models

Avoiding Confusion Between Correlation and CasualityCorrelation, that there is a link, and causality, that causes produce effects, are very different.

Basic Model Building.  The step-by-step building of a Powersim Studio model is explained and demonstrated.

Formatting Variable Definitions.  Often the algebraic expressions formulated for rate-controlling or auxiliary variables can be quite long.

Governing Business Rules in System Dynamics Models.  When constructing models, we need to include the most important structural elements. These need to be connected according to the most influential governing business rules.

Graphing Time-Dependent Variables.  We often need to provide graphical inputs into models. Limited data sets may be depicted conveniently in graphical form, because this allows the data to be interpolated.

Integration and Differentiation—Linking Stocks and Flows.  The structural linkage results either in mathematical integration (summation or accumulation) or mathematical differentiation (an indication of rate of change of a variable).

Making Graphs Easier to Read.  Sometimes graphs of changes over time have values that are the same, or nearly the same, for part of a given simulation, as other graphs. This can result printouts being superimposed on each other.

Soft Variables and Intangibles in System Dynamics Models.  Soft variables are a class of variables, which includes a sub-class known as intangibles. These relate to attributes of human behaviour or effects that variations in such behaviour produce. As far as soft variables are concerned, numerical data are often unavailable or non-existent.

Time in System Dynamics Models.  System dynamics modelling is time-domain modelling in which we set out to formulate and analyse how cause-and-effect relationships work to produce variations over time.

Trend Extrapolation.  Extrapolation means to infer or estimate by extending or projecting known information. In mathematical terms this involves making estimates of a value of a variable outside a known range from values within a known range.

Using Graph Functions for Input of a Dependent Variable.  We often need to provide graphical inputs into models. Limited data sets may be depicted conveniently in graphical form.

Using TIME, STARTTIME and TIMESTEP Functions in System Dynamics Models.  In Powersim Studio, time has five distinct meanings

Verification—Mass-Balance Testing of System Dynamics Models.  Two essential model-building activities are verification and validation. Unfortunately these two terms are often used interchangeably, which leads to confusion.

 

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