hello so now that we've started to
explore agent-based modeling a little
bit more we've gone
what the class is going to be about
let's take a step back and let's go back
to discuss what an agent-based model is
in the first place but before we discuss
when agent-based model is I think it's
important to discuss what a model is and
I find this important because in many
ways understanding an agent-based model
involves understanding what the point of
modeling is to begin with and this is
something that many of you may have
learned at some point in your careers
but it's important to kind of take a
refresher and take a step back and
discuss this so I define an agent-based
model as an abstracted description of a
process object or event and the
important point here is that it's
abstracted it's not a perfect
representation it doesn't exactly match
up with the real world and the important
thing is the exaggerate certain aspects
at the expense of others so for instance
in this particular slide I have a
picture of the nernst and imagine that
this is actually the real earth that
you're trying to model and on one side
we have a a particular projection onto a
two-dimensional map of the earth and
what that allows you to see very easily
is kind of the delineation between where
the earth is land and where it's
water--the of course that be changing in
time as you might expect but it doesn't
allow certain other aspects for instance
it doesn't really talk about what's
inside the earth on the right-hand side
I have an image that you might see from
a traditional intro to or science
textbook or something along those lines
where we show a cutaway the earth and we
can kind of see what the crust is what
the other aspects are now neither of
these models is a perfect model right
both of these models are wrong to some
extent and in fact George box a famous
statistician had a quote to that to the
interpretation right that essentially
all models are wrong but some are useful
the perfect model is not the model that
best represents the world around us but
instead is a model that in some ways
exaggerates the aspects of the world
that we're most interested in it can
help us solve the problems that we're
looking at in fact my adviser John
Holland used to say that models are in
some ways like political cartoons
right they exaggerate and blow up
certain aspects while back rounding and
hiding of their aspects for you to make
so that you can concentrate on the
aspects that they're trying to make a
point about right so given that
description of a model right then what
is an agent-based model well AJ based
model in our context is a model that's
composed of agents as you might expect
an agent is an autonomous individual
element with properties and actions in a
computer simulation so we're in most of
the context we're going to talk about
leases in a computer simulation and an
agent-based modeling is the idea that
the world itself can best be modeled by
using agents in environment and
description of agent agent agent
environment interactions and the sexual
conceits of agent-based modeling right
is that this is one of the best ways to
describe a lot of the complex systems
that we see around us now over here I
have some descriptions of some different
types of things that we might think of
agents now generally when people think
of agents they often think of humans
right in individual humans in that
context but agent doesn't have to be an
individual human it could be a company
for instance in which case the agent
based model might be a model of the
interactions between the different
companies it could in fact be a human so
in this and this graph right here I
actually have a screen capture of the
net logo HIV transmission model in which
case the model is in fact of agents who
have ever sending humans who might
spread HIV from one together now know
especially with there's no reason why
the model had to a bid built at the
level of humans it was probably
appropriate for the particular purposes
for which the model was being
constructed but it could have been built
at the level of say for instance viruses
right in which case it would be a very
different model and at a different level
of resolution and would probably help
you answer different questions a model
could also be a government so here I
have a representation of the the Capitol
dome
in Washington DC right and we could
instead be modeling the interaction
between governmental agents now over
here I have a representation of Kim
jong-il right and I put Kim jong-il up
there not as an indication of what you
might represent with an age of base
model but as a representation of what
it's often not useful to represent it as
an age of base model so many agent based
models try to characterize overall
patterns of behavior right and when you
have one individual who in many ways is
kind of erratic is different from the
overall behavior it's very hard to kind
of predict or understand what that
individual is going to do now in those
cases there are other modeling
approaches such as ethnographic modeling
or in-depth psychological studies that
might give you better understanding but
in many cases I suggest not using agent
based models in for these on the other
hand if you wanted to build a set of
agent based models in which you try to
understand the role of dictators and
despots and something like along those
lines on a more kind of generalized
basis rather than for one particular
individual then Asia based modeling
might very well be useful for that
context