Systems & complexitySystems thinking and modelling

Modeling With Agents: Integrating System Dynamics modeling and Agent Based Modeling [Systems thinking & modelling series]

This is part 70 of a series of articles featuring the book Beyond Connecting the Dots, Modeling for Meaningful Results.

System Dynamics modeling and Agent Based Modeling are two different ways of approaching a system. In general, System Dynamics looks at highly aggregated systems and encourages the study of feedback. Agent Based Modeling explores individuals and the interactions among these individuals.

Some software packages support either System Dynamics or Agent Based Modeling, but not both, leading to the perception that they are somehow incompatible methodologies. Although these techniques can be thought of as quite different, it is important to realize that both are simply applied mathematics. To emphasize this, Insight Maker integrates these techniques together seamlessly in its modeling environment. There is no such thing as an “Insight Maker Agent Based Model” or an “Insight Maker System Dynamics Model”. There are simply models where you may use agent-based techniques, System Dynamics techniques, or a mixture of the two.

Insight Maker (and other modeling packages such as AnyLogic allows you to integrate the two seamlessly together. For instance, in this section we have used state transition diagrams within our agents. We could have just as well used stock and flow diagrams within the agents so that each agent in effect contained its own System Dynamics model of its state. Similarly, if you have a large System Dynamics model you could create an agent-based sub-model that feeds into the main model dynamics.

When modeling, it is important not to focus on labels or taxonomies of different techniques. Given a modeling task, you want to think about what tools and techniques are best suited. Make sure not to approach a modeling task by trying to figure out how to force that task into the constraints of a favorite modeling paradigm.

Exercise 10-14
Compare and contrast the Agent Based Modeling and System Dynamics approach to creating models. Provide three examples of modeling tasks where Agent Based Modeling would be better suited than System Dynamics and three examples where the reverse would be true.

Next edition: Modeling With Agents: Concluding Thoughts.

Article sources: Beyond Connecting the Dots, Insight Maker. Reproduced by permission.

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Scott Fortmann-Roe and Gene Bellinger

Scott Fortmann-Roe, creator of Insight Maker, and Gene Bellinger, creator of SystemsWiki, have written the innovative interactive book "Beyond Connecting the Dots" to demystify systems thinking and modelling.

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