IBMs..

[Paul Fishwick]

Chris and all:
 Let me address your points:

> why is data calibration more of a problem for IBM
> models than for other modelling technologies? What sorts
> of problem domains are you particularly concerned about?

As a general statement, it is always more difficult to collect data
from small scale phenomena than for large scale phenomena
regardless of domain. Consider the ecological domain as an
example. Improved sensing, radio and satellite methods are
providing data for individuals, where this was not possible
in the past; however, getting population data is generally
easier than obtaining specific data from individuals in
the population. The concepts of population and sample in
statistics gives us some justification for this. What holds true for 
ecology most likely holds true for other fields---that is, procuring 
the data can be expensive, time consuming and difficult.

> I can allow as how it would be difficult to calibrate
> an IBM model of a forest precisely so that each tree-agent
> is parameterized via data taken from its respective
> real-tree in the forest. Yet, all modelling technologies
> make do with some degree of approximation. A reservoir-flow
> model of tree-species interaction in a forest would simply
> treat all of the trees of each species as "one big tree" 
> of that species with respect to some data (such as  concentration, 
> nutrient uptake, waste-production, and etc.) while ignoring
> other data (such as spatial distribution, variety within the 
> species, and etc.) This will be justified for certain questions 
> about forest dynamics, but not for others, and might make more 
> sense for some problem domains than for others. 

Yes, agreed.

> You seem to be suggesting that this is fundamentally more of a problem
> for IBM models than for other modelling technologies.

...In the sense that it is generally less economic and more difficult to
obtain individual data for basic reasons of time, cost and other factors.
New sensing methods are helping but, yes, I would say that IBMs are
more difficult to create and calibrate due to the sheer amount of data
that are needed. I have copied by colleague in Miami to comment on this
aspect since I am not a field person--i.e., not going out to tag gators :)
This is not a theoretical issue; it is one of practicality relating to
cost, time and availability of data.

>  ...and, please!, it almost *hurts* to use the acronym IBM!
> could we use "ABM" for Agent-Based Models? I think it fits

As you say, IBMs have precedence in the ecological community and so I
see no need for changing this term when speaking of ecological matters.
Regarding something more generic, I actually prefer the word "Object".
"Agent" sounds like something human. Anyway, I realize we are discussing
semantics at this point.

-paul


Paul A. Fishwick               E-Mail: address@hidden
Dept. of Computer & Info       Phone & FAX: (352) 392-1414
 Science and Engineering       WWW: http://www.cise.ufl.edu/~fishwick
University of Florida          (PGP Key available at above WWW address)
P. O. Box 116120
332 Bldg. CSE, Gainesville, FL 32611-6120





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