Exploring Complex Systems through
Games and Computer Models
Santa Fe Institute – Project GUTS
http://www.projectguts.org
What is a complex system?
Complex
difficult-to-understand or difficult to predict
System
A group of interacting, interrelated, or interdependent parts
forming a whole.
So a “Complex System”
is collections of simple units or agents interacting in a system. Large-scale
behaviors of the system are difficult to understand or difficult to predict and
may change, evolve, or adapt. (Also called Complex Adaptive Systems)
Some problems we face
Climate change
Pollution
Spread of disease
Loss of biodiversity
Civil violence
All of these issues are studied as “complex systems” using computer models.
Traffic jams
Forest fire evacuation
These local problems can also be studied as complex systems:
How do scientists study
complex systems?
Scientists recreate complex systems in a "virtual world" on a computer where they are able
to run many experiments without impacting the real world.
How do scientists study
complex systems?
How do scientists study
complex systems?
QuickTime™ and a
Cinepak decompressor
are needed to see this picture.
The Computational Science Process
Begin here
StarLogo is a tool used to create a Computational Model
Creating Computer Models with StarLogo TNG




Create agents and environment
Give agents and environment simple rules to follow
No sophisticated mathematics or programming required
Explore the behavior of complex systems
The
Predator,
Prey, and
Grass
Model
Modeling and Computational Science
• A model is a representation of the interaction of
real-world objects in a complex system.
• The goal is to gain an understanding of how the
model’s results relate to real-world phenomena.
• Random factors built into the model and variables
changed by the user cause different results to be
generated when the model is run repeatedly.
Model Classification*

Idea Models
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
Minimal Models for Systems


e.g. Model of Predator and Prey
e.g. Model of Wolves and Caribou
Systems Models

e.g. Model of every Wolf and Caribou in 5
square mile section of Yellowstone
*This classification scheme was proposed by J. Roughgarden.
Increasing
complexity
and detail
Decreasing
generality
and
applicability
Why wouldn’t you want to run these
experiments in real-life?
What are Characteristics of
Complex Adaptive Systems?
Characteristics of
Complex Adaptive Systems
Leaderless (aka decentralized)
A classic example
Birds Flocking
A classic example
flocking - Craig Reynolds
Separation: steer to avoid
crowding local flockmates
Alignment: steer towards
the average heading of local
flockmates
Cohesion: steer to move
toward the average position
of local flockmates
http://www.red3d.com/cwr/boids/
Characteristics of
Complex Adaptive Systems
Emergent patterns develop from the simple
interactions of agents
A classic example
Termites
Termites model
Characteristics of
Complex Adaptive Systems
Non-linear The sum of the parts is not equal
to the whole.
In Mathematics
Non-linear means:
f(a+b)  f(a) + f(b)
Ex.) the exponential function is non-linear.
f(2 + 3)

f(2) + f(3)
f(5)

f(2) + f(3)
25

4+9
*Non-linear systems are systems that cannot be mathematically
described as the sum of their components.
Characteristics of
Complex Adaptive Systems
Self-organization The system organizes itself.
A classic example
Schelling Segregation Model
Developed by Thomas C. Schelling
(Micromotives and Macrobehavior, 1978).
4 Characteristics of
Complex Adaptive Systems
Leaderless there is no leader (boids)
2. Emergent patterns develop from the simple
1.
interactions of agents. (termites)
3.
Non-linear The sum of the parts does not
equal the whole.
4. Self-organization The system organizes
itself
Complex System or just
Complicated?
Complex System
or just Complicated?
Complex System or just
Complicated?
Complex System
or just Complicated?
Complex System or just
Complicated?
Some examples of
Complex Adaptive Systems
 Global
climate patterns
 A termite mound
 Highway traffic patterns
 The spread of a disease in a population
 The evolution of ideas in a society
 A food web in an ecosystem
The End