“Modeling Complex Systems” by Diana StirlingA Review and Discussion of the Paper

James Hornage - 090309

Complex Adaptive Systems

Characteristics of Complex Adaptive Systems: They persist in spite of changes in the diverse

individual components The interaction between the components is what is

responsible for the persisitence of the system The system engages in adaptation or learning.

The Concept of Co-Evolution

Kauffman (1995) argues that “A living system must first be able to strike an internal compromise between malleability and stability.

Co-evolution is necessary because when an agent changes, the environment around that agent changes as well.

Co-evolution concepts underlie the premise that there is an optimum size and number of “patches” to maintain maximum response ability.

Putting the Systems in Perspective

Size and scope can range from neurons to social systems

Agent (system) is likely unaware of the extent of the entire system

Systems need only to provide excellent solutions as opposed to optimal solutions Let not the pursuit of the perfect solution stand in

the way of a “perfectly good solution”.

The Power and Difficulty of Modeling

The Power Modeling complex systems provides into problems

particularly when people have trouble visualizing them.

Modeling provides a way to understand the impact of variables in a clear manner

The Difficulty Disagreements in definition can arise, such as the

difference between Gell-Mann’s terminology and Holland’s terminology for an “adaptive agent”

Modeling Tools

Starlogo and Netlogo provide users with the opportunity to see self-organization in a visual model

Both products use the Logo language, which was developed out of MIT in order to teach the basics of computing to children

The main components of these models are turtles, patches, and the observer.

Starlogo FireFlies

Starlogo Ants

Summary

Complex adaptive systems: Involve agents, whose behavior is motivated largely

by reaction to the local environment Oscillate between order and chaos, which actually

provides for stability and flexibility Rely on excellent solutions rather than the optimum

solution Base their judgment about a solution as excellent by

creating a schemata based on activities that are regularly identified with success.

Discussion

What other models do you think would be interesting based on the Ants and Fireflies models from Starlogo?

What are your thoughts on the concept of co-evolution? It seems the environment depends on the agent almost as much as the agent depends on the environment?

Do you have a different way that you would define or describe the term complex adaptive systems?