Model to Model Workshop, EHESS, Grequam/CNRS, Marseille 2003, slide-1 Model  Model Workshop - relating simulation models At EHESS, GREQUAM/CNRS Marseille, 2003 Welcome to the…

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

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

Model to Model Workshop, EHESS, Grequam/CNRS, Marseille 2003, slide-4 Outline 1.Kinds of model, in particular comparing equation-based modelling and individual/agent-based simulation 2.Some basic ways in which models may be related or compared 3.Some uses for relating or comparing models

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

Model to Model Workshop, EHESS, Grequam/CNRS, Marseille 2003, slide-6 Equation-based modelling Model Target Equation-based Model Actual Outcomes Aggregated Actual Outcomes Aggregated Model Outcomes

Model to Model Workshop, EHESS, Grequam/CNRS, Marseille 2003, slide-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, slide-8 Individual-based simulation Model Target Agent-based Model Actual Outcomes Model Outcomes Aggregated Actual Outcomes Aggregated Model Outcomes Agent-based

Model to Model Workshop, EHESS, Grequam/CNRS, Marseille 2003, slide-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, slide-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, slide-11 Some Uses of Simulation To predict what is currently unknown To explain what is already known To calculate outcomes 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, slide-12 Part 2: Some Ways in which Models may be Compared or Related

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

Model to Model Workshop, EHESS, Grequam/CNRS, Marseille 2003, slide-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, slide-15 As a Generalisation/Specialisation of Another Model

Model to Model Workshop, EHESS, Grequam/CNRS, Marseille 2003, slide-16 As a Controlled Experiment/Comparison ?

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

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

Model to Model Workshop, EHESS, Grequam/CNRS, Marseille 2003, slide-21 Comparison to Inform Generalisation comparison Generalised Model

Model to Model Workshop, EHESS, Grequam/CNRS, Marseille 2003, slide-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 … ?