Swarm Intelligence

Winter 2004Lab 03/04 Lecture Supplement

Apr 5, 2004

Swarm Intelligence

• New field of study (<10 years old)• Study of models based on natural models

(usually of social insects)• Part of Self-Organization that studies

emergent phenomena in systems of interacting agents

Components

• Agents:– Interact with the world and with each other

(either directly or indirectly) – Simple behaviours– e.g. ants, termites, bees, wasps

• Communication:– How agents interact with each other– e.g. pheromones of ants

Main Idea

• Simple behaviours of individual agents + Communication between a group of agents = Emergent complex behaviour of the group of agents

• i.e. global behaviours arising from interactions between agents using simple local behaviours without any global controller

• This is an example of self-organization

Communication

• Direct:• e.g. Touching, vision, smelling other agents• Pretty obvious interactions

• Indirect:• Stigmergy:

– One agent modifies the environment– Another agent reacts to the modification of the environment– e.g. ants leaving pheromones in the environment (when

returning to the nest with food) which are picked up by other ants and followed to the food source

– e.g. termites leaving soil pellets on the ground and triggering different placements based on the size of the pellet structure, resulting in nest construction

Algorithms• Using agents and usually stigmergic behaviours• Agent interactions are modeled by a set of

action -> reaction rules• e.g. if concentration of pheromones is low, I wander around;

if concentration is high enough, I go towards the highest concentration

• The rules are applied locally – the agents do not have global information, only know about their local environment

• Through this local rule application, global emergent behaviours are observed

Applications• Optimization problems

• Computer approximate solutions to problems such as combinatorial problems (e.g. TSP) and routing (e.g. network routing)

• Construction algorithms• Using self-organization and stigmergy to build structures

using a set of simple rules (based on wasp/termite nest building)

• Self assembling robots

• Cooperative transport• Accomplishing tasks (in this case transport) that require

multiple agents cooperating with each other and without global information

• Robotic cooperative transport

Boids

• Model by Craig Reynolds• http://www.red3d.com/cwr/boids/

• Model of life-like artificial flocking of agents (called boids) using 3 simple rules

• Demonstrating interesting global flocking behaviour from simple local rules

• Each boid can see other boids inside its sphere of neighbourhood

• Can be easily adapted to demonstrate other swarming behaviours such as fish schooling

Boid Rules

• Separation:• Avoid crowding

local agents

• Alignment:• Steer towards average

heading of local agents

• Cohesion:• Steer to move towards

average position of local agents

Good Books

• Swarm Intelligence: From Natural to Artificial Systems by Bonabeau, Dorigo, Theraulaz (~$40)

• http://www.amazon.ca/exec/obidos/ASIN/0195131592

• Self-Organization in Biological Systems by Camzine, Deneubourg, Franks, Sneyd, Theraulaz, Bonabeau. (~$50)

• http://www.amazon.ca/exec/obidos/ASIN/0691116245