On The Transition to Agent-Based Modeling: A
Case Study
László Gulyás
gulyas@fas.harvard.edu
In this paper I study the effect different implementation
approaches have on the actual setup of an individual-based computer model.
My goal is to demonstrate how these techniques 'guide our hands' and hide
our implicit decisions (assumptions about the modeled system). The connection
between the conceptual model and its actual implementation is important,
especially, as the later rarely gets published. On the other hand, I am interested
in 'what makes a model agent-based'. Is it enough to model a system composed
of individuals? Or should the agents' behaviour and/or the effect of their
behaviour be at the centre of our attention? To answer these questions I
have re-implemented a simple, individual-based model [of Paul Krugman’s]
in RePast. While the model was originally published in a variable-based form,
I have created four different versions of it ranging from the variable-based
one to a version containing autonomous agents. My results provide evidence
that even if the system consists of individual entities (say, agents) and
the author's main concern is their behaviour and/or the aggregate effect
of these behaviours, the model itself could actually ignore the agents.