Emergent Behaviours and their Simulations

An introduction to Agent-based Modeling

N Chandrasekhar Ramanujan @ IGCS June 8 2016

If you have seen a Mexican Wave you have seen an agent-based model at work.. • Link to mexican wave video• People in the stadium = the agents• Two simple rules : Stand when guy on left stands…. Sit when the guy

sits.

Why do we make models?

• For insights • For explanations• To make predictions

What does ABM do?• ABM helps us understand Complex Adaptive Systems• complex adaptive systems we refer to a group of (locally) interacting

agents, who act and react to actions of other agents.• The coherent emergent behavior that might occur in a system arises

from the local interactions of the agents• Unlike many other modeling techniques that quantify and then re-

create the patterns, agent-based models explore the causes of the patterns; the patterns are emergent properties from the individual decisions of the agents.

What is an agent?• An agent is...

– An individual with a set of characteristics or attributes

• A set of rules governing agent behaviors or “decision-making” capability, protocols for communication

● Respond to the environment ● Interact with other agents in the system

• Agents are diverse and heterogeneous • This makes it interesting!

Key elements of an ABM – the model• Identify the agents and define their actions• Agent consists of • Attributes• Behaviours – how do you parameterise these?

• Running the model – time is a discrete variable• Change conditions, tweak variables, see what happens!

Emergent behaviour – flocking model in Netlogo• Introduce Net Logo – open source software• You will see a simulation of birds • They have been given three simple rules to control how they interact

with each other : essentially collision avoidance rules. • At the start of the simulation the birds are given random speeds and

directions. • However after a few moments the birds begin to fly in a formation

that is similar to the flocking formation seen in the real world.

Agent-based models are now the tool of choice to model and simulate behaviours and outcomes in a number of contexts….

• Driving factors….• Huge Improvements in computing power • Huger improvements in data sets …. E.g. you can get real time data

on traffic for instance …. You can predict what-if scenarios and congestions

• Qn. : Where can we use here in Insti? Mess in the mess?

Another example of ABM on Net Logo

• Take a simple wolf and sheep Model … and simulate small changes in rules• …. Simulate small changes in the environment… e.g. the fertility rates

of sheep affected by climate change….

Why ABMs are preferred to general equilibrium, DSGE models etc

• Can use actual behaviours data and not assumptions of Rational Man behaviours • Coping with climate change …. How people may adopt different

behaviours response is not strictly determined by rational –economic coconsiderations

Some Strengths of ABM• System assumptions• Heuristic ability• Heterogeneity• Bounded Rationality• Communication & Social Networking

Some Shortcomings of ABMs • Data Problems: potential lack of adequate data due to nature of

model itself• Identifying rules of behaviours• Hard to prescribe solutions?

ABM and GIS• GIS is a spatial modeling tool that stores and displays geographic data

and analyzes spatial relationships• Natural Synergy between ABM and GIS• Linking agent-based models to GIS means we can create models

directly related to space• Spatial data acts as a “container” for agents• Allows us to compare aggregate outputs to the “real” world, helping

us validate our models

What can you do with ABM & GIS?• With ABM + GIS, you can:•Model and understand Land Use Change (Earlier Sriperumbudur

project by Keerthi, Amala)• Analyzing traffic congestion• Simulate spread of infectious diseases within populations

Scenario planning and ABM• Planning is a very big, scary thing!• marked by complexity, multiple stakeholders and outcome uncertainty • ABM can help – how?• It is a method of a method that

• integrates a variety of data• allows for evaluation of comparable options• visualizes complex interactions and future outcomes

• develop thinking and expectations of how actors behave• see how linkages between actors affect behaviour

Applying ABM in other contexts• In LOTR movies, where battles had 1000s of actors, used ABM with

special effects to model movements of people effectively• Budweiser ad – super bowl

One for the Road…

• some fun assignments … how would you model these? What variables and behaviours would you take into account?• Crowd movement in saarang - • Traffic jam at Madhya Kailash• First day attendance at a new film release..• Stock of energy drinks at Gurunath …. Ebb and flow at different times of day/

week/ month / year….. Other Non temporal events like tests or quizzes

Thanks for Listening! Welcome Questions, comments, suggestions