New Mexico Computer Science for All

Exploring Complex Systems through Computer ModelsBy Irene LeeDecember 27, 2012

Introduction to complex systemsWhat are theyWhy do we study themHow do we study them

Outline

What is a complex system?

Complex (adj.)difficult-to-understand or difficult to predict

System (noun)A group of interacting, interrelated, or interdependent parts forming a whole.

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.

Characteristics of Complex Adaptive Systems

Leaderless (a.k.a. decentralized)

Characteristics of Complex Adaptive Systems

A classic exampleBirds Flocking

A classic exampleflocking - 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/

A classic exampleBoids - Craig Reynolds

http://www.red3d.com/cwr/boids/

Emergent patterns develop from the simple interactions of agents

Characteristics of Complex Adaptive Systems

A classic exampleTermites

Termites model

A classic exampleMound building in StarLogo TNG

Non-linear The sum of the parts is not equal to the whole.

Characteristics of Complex Adaptive Systems

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.

Self-organization The system organizes itself.

Characteristics of Complex Adaptive Systems

A classic exampleSchelling Segregation Model

Developed by Thomas C. Schelling(Micromotives and Macrobehavior, 1978).

A classic exampleSchelling Segregation Model

1. Leaderless there is no leader (boids)

2. Emergent patterns develop from the simple interactions of agents. (termites)

3. Non-linear The sum of the parts does not equal the whole.

4. Self-organization The system organizes itself

4 Characteristics of Complex Adaptive Systems

Why is it important to learn about complex systems and

approaches to understanding complex systems?

Climate change Loss of biodiversity Pollution Civil violenceSpread of disease Emergency Egress Traffic jams Forest fire

Many of the daunting problems of the 21st Century can be studied as complex

systems problems.

Epidemics

Hufnagel, L. et al. 2004 PNAS 101:15124 Forecast and control of epidemics in a globalized worldCopyright ©2004 by the National Academy of Sciences

NATURE|Vol 460|6 August 2009

Epidemics

Networks

upload.wikimedia.org/.../Internet_map_4096.png

Ocean Circulation - Ecosystems

Transportation Systems

Workflow Simulation

Crowd Dynamics

Crowd Dynamics

Crowd Dynamics

We will learn about agent-based modeling and simulation as an

approach to understanding complex systems

The Computational Science Process

NetLogo is a tool used to create a Computational Model

Begin here