Model  Model Workshop - relating simulation models

1. Model  ModelWorkshop- relating simulation models Welcome to the… At EHESS, GREQUAM/CNRS Marseille, 2003 Model to Model Workshop, EHESS, Grequam/CNRS, Marseille 2003, http://cfpm.org/m2m slide-1

2. Organisation Juliette Rouchier durandal.cnrs-mrs.fr/GREQAM/cv/rouchier.htm David Hales www.davidhales.com Bruce Edmonds bruce.edmonds.name EHESS, GREQUAM/CNRS durandal.cnrs-mrs.fr/ehess/ehess.html Centre for Policy Modellingcfpm.org Model to Model Workshop, EHESS, Grequam/CNRS, Marseille 2003, http://cfpm.org/m2m slide-2

3. Relating Models- an overview Bruce Edmonds(including material from David Hales and Juliette Rouchier) Model to Model Workshop, EHESS, Grequam/CNRS, Marseille 2003, http://cfpm.org/m2m slide-3

4. Outline • Kinds of model, in particular comparing equation-based modelling and individual/agent-based simulation • Some basic ways in which models may be related or compared • Some uses for relating or comparing models Model to Model Workshop, EHESS, Grequam/CNRS, Marseille 2003, http://cfpm.org/m2m slide-4

5. Part 1: Overview and Comparison of Equation-based Modelling and Agent-based Simulation Model to Model Workshop, EHESS, Grequam/CNRS, Marseille 2003, http://cfpm.org/m2m slide-5

6. Equation-based modelling Equation-based Model Model Target Actual Outcomes AggregatedActual Outcomes AggregatedModel Outcomes Model to Model Workshop, EHESS, Grequam/CNRS, Marseille 2003, http://cfpm.org/m2m slide-6

7. Properties of (equation-based) Mathematical Models • Long tradition, many techniques/results • Central use of numbers and proof • In simple cases can derive closed-form (i.e. general) conclusions • Essentially about states • Atemporal (where time occurs it is reified) • Inference can works in may ways • Assumptions necessary to represent world • ‘Art’ of approximation and application Model to Model Workshop, EHESS, Grequam/CNRS, Marseille 2003, http://cfpm.org/m2m slide-7

8. Agent-based Individual-based simulation Agent-based Model Model Target Actual Outcomes Model Outcomes AggregatedActual Outcomes AggregatedModel Outcomes Model to Model Workshop, EHESS, Grequam/CNRS, Marseille 2003, http://cfpm.org/m2m slide-8

9. Properties of (agent/individual-based) Simulations • Short tradition, fewer techniques/results • Central use of algorithms and computation • Difficult to derive general conclusions • More like an experiment than an inference • Essentially about process • Temporal directionality • Process of unfolding observable • More representational in practice • In time and in composition • More suggestive of interpretation Model to Model Workshop, EHESS, Grequam/CNRS, Marseille 2003, http://cfpm.org/m2m slide-9

10. Some Uses of Mathematics • To predict what is currently unknown • To explain what is already known • To derive/infer conclusions from axioms • To represent observed phenomena • To explore unobserved possibilities • To make an idea unambiguous • To compress a representation • To show one model is a special case of another • To construct a formal framework/language Model to Model Workshop, EHESS, Grequam/CNRS, Marseille 2003, http://cfpm.org/m2m slide-10

11. Some Uses of Simulation • To predict what is currently unknown • To explain what is already known • To calculateoutcomes from initial set-up • To represent observed phenomena • To explore unobserved possibilities • To make an idea unambiguous • To compress a representation (in theory) • To show one model is a special case of another (in theory) • To construct a formal framework/language Model to Model Workshop, EHESS, Grequam/CNRS, Marseille 2003, http://cfpm.org/m2m slide-11

12. Part 2: Some Ways in which Models may be Compared or Related Model to Model Workshop, EHESS, Grequam/CNRS, Marseille 2003, http://cfpm.org/m2m slide-12

13. Outcomes from one run Agents Setting Code A diagram for a simulation model Model to Model Workshop, EHESS, Grequam/CNRS, Marseille 2003, http://cfpm.org/m2m slide-13

14. As a Summary/Abstraction of Another Model’s Results • Modelling model results • More abstract model can be of any kind (including simulations and equation-based models) • Can be a tactic to help understand/analyse complex models Model to Model Workshop, EHESS, Grequam/CNRS, Marseille 2003, http://cfpm.org/m2m slide-14

15. As a Generalisation/Specialisation of Another Model Model to Model Workshop, EHESS, Grequam/CNRS, Marseille 2003, http://cfpm.org/m2m slide-15

16. ? As a Controlled Experiment/Comparison Model to Model Workshop, EHESS, Grequam/CNRS, Marseille 2003, http://cfpm.org/m2m slide-16

17. Summary of Some Basic Kinds of Model Relation/Comparison • Abstraction/approximation of another model • Super/subset of another model • As a Controlled Comparison • The code of one model is a component of the code of another • Others … ? Model to Model Workshop, EHESS, Grequam/CNRS, Marseille 2003, http://cfpm.org/m2m slide-17

18. Part 3: Some Uses for Relating Models Model to Model Workshop, EHESS, Grequam/CNRS, Marseille 2003, http://cfpm.org/m2m slide-18

19. To check models are equivalent • Examination of the code suggests a hypothesis that the simulations are equivalent but… • …this can only be disconfirmed by experiment • Repeated failure to disconfirm hypothesis can lead one to rely on it • Reveal hidden assumptions – understand the limits of our creations! Model to Model Workshop, EHESS, Grequam/CNRS, Marseille 2003, http://cfpm.org/m2m slide-19

20. Equation-based models Descriptive simulation Observations of the phenomena As a tool for staging abstraction Model to Model Workshop, EHESS, Grequam/CNRS, Marseille 2003, http://cfpm.org/m2m slide-20

21. GeneralisedModel comparison Comparison to Inform Generalisation Model to Model Workshop, EHESS, Grequam/CNRS, Marseille 2003, http://cfpm.org/m2m slide-21

22. Summary of Some Uses of Relating Models • Check if models are the same • To reveal assumptions • As a tool for staging abstraction • To inform generalisation • Communicate and compare complex phenomena between researchers • And … ? Model to Model Workshop, EHESS, Grequam/CNRS, Marseille 2003, http://cfpm.org/m2m slide-22