To the Outer Limits and Beyond
– characterising the envelope of sets of social simulation trajectories

CPM Report No.: 06-161
By:  Bruce Edmonds, Oswaldo Terán and Gary Polhill


In social simulation one is often not interested in single runs but properties common to set of simulation trajectories resulting from a single simulation set-up.  One such property is the envelope of all possible such trajectories – which can be thought of as the outer ‘skin’ to the bundle of trajectories in some space of values.  This paper considers an approach towards characterising this envelope, which would result in the type of "general results" usually lacking in simulation work.  It presents a general framework for a structured approach to the different kinds of information used in simulation specification in terms of the: Fixed Structure; Active Constraints; Logical Relations; Generative Rules, Extra Constraints; and Checking Constraints.  It describes how the development of a simulation would use these categories.  

An example model developed in both procedural and Constraint-Logic Programming (CLP) is used to illustrate this approach.  The model implements a real game that is played called ‘liar dice’.  The CLP model described uses SWI-Prolog plus Constraint Handling Rules (CHR).  CHR allows the integration of flexible constraint propagation in conjunction with the normal Prolog depth-first search for solutions.  Use of this framework avoids having to specify arbitrary cognitive rules merely in order to get a simulation to run.  Hence its use can simultaneously simplify a model and make it more representative of what can be elicited about social situations.  

Other benefits of the approach could include: more reliable simulations; the explicit communication and management of assumptions; and the facilitation of model-to-model comparison.

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