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2-Day Introduction to Agent-Based Modelling

2-Day Introduction to Agent-Based Modelling. Day 2 : Session 7 Social Science, Different Purposes and Changing Networks. Discussion: the Social Science view of ABM. Different purposes for an ABM. A lot of confusion occurs because there are many different uses for an ABM, e.g.

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2-Day Introduction to Agent-Based Modelling

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  1. 2-Day Introduction to Agent-Based Modelling Day 2: Session 7 Social Science, Different Purposes and Changing Networks

  2. Discussion: the Social Science view of ABM 2-Day Introduction to Agent-Based Modelling, Manchester, Feb/Mar 2013, slide 2

  3. Differentpurposes for an ABM • A lot of confusion occurs because there are many different uses for an ABM, e.g. • To predict something unknown from what is known (such as predicting final election results) • To explain some effect in terms of some other, more basic/more micro, processes • To illustrate an idea of how something might happen – an analogy in computer form • As a counter example to how people assume things must work • As an exploration of possibilities that one might not have thought of/imagined otherwise • Unfortunately authors often do not clearly state which they are intending with a model, indeed they often seem to conflate them!  2-Day Introduction to Agent-Based Modelling, Manchester, Feb/Mar 2013, slide 3

  4. Network Change Model • Agents connect to each other and change their links • Some agents freely give to those they are linked with (at a small cost to themselves), the rest do not at start only 10% are givers, and all linked randomly • After that all agents follow same rules (apart from giving/not giving) • But after a while the system self-organises to avoid non-givers and givers predominate 2-Day Introduction to Agent-Based Modelling, Manchester, Feb/Mar 2013, slide 4

  5. Behavioural Rules • Givers cause their neighbours to receive units of value at random • With a probability (prob-compare) an agent picks another at random. If its value (from gifts) is less than the one picked it imitates its strategy (giving/not), kills links and links to it • With a probability (prob-rand-reset) kill all links and link to a random agent • If it has too many links, drop one at random • If it has too few link to someone agent is linked to (so called “friend of a friend”) • With a probability (prob-change) swap colours 2-Day Introduction to Agent-Based Modelling, Manchester, Feb/Mar 2013, slide 5

  6. Network Change Model Display Agents with “happy” face have gained a value above average, those “sad” with a value below Givers shown as green, non-givers as red Note how system has self-organised so that givers tend to cluster together Load and play with simulation “7-network change.nlogo” 2-Day Introduction to Agent-Based Modelling, Manchester, Feb/Mar 2013, slide 6

  7. Questions! • Given that there are no rules that obviously favour givers (indeed it costs them to give), why do givers eventually predominate? • What experiments could you make to the code to try and discover what makes this happen? Try “commenting out” rules and see what happens. • What does this simulation demonstrate (if anything)? • How might you prove the effect in a paper? 2-Day Introduction to Agent-Based Modelling, Manchester, Feb/Mar 2013, slide 7

  8. Collecting Statistics • From menu: File >> Export >> • Export View: saves the view of the world as a picture for use statistics • Export Plot: saves the data from a plot as a “.csv” file for use in plotting/analysis programs • Export Output: saves text in output area to a text file (if there is a log of text there from “show” statements in the code) • For multiple runs, maybe with different parameters, with data automatically appended to a “.csv” file, use Tools >> BehaviourSpace(read about this in manual first) 2-Day Introduction to Agent-Based Modelling, Manchester, Feb/Mar 2013, slide 8

  9. The End 2-Day Introduction to Agent-Based Modelling http://cfpm.org/simulationcourse Methods@Manchester http://methods.manchester.ac.uk/ Centre for Policy Modelling http://cfpm.org Manchester Metropolitan University Business School http://www.business.mmu.ac.uk Institute for Social Change http://www.humanities.manchester.ac.uk/socialchange/ Cathie Marsh Centre for Census and Survey Research http://ccsr.ac.uk University of Manchester http://man.ac.uk

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