Re: Central Control

[EMERGE_sl_users@umit.maine.edu (Larry Latour)]

dfisher@cert.org,.Internet writes:
>In research that we are doing related to emergent algorithms, we
consider
>global visibility on a par with central control and generally do not
>consider algorithms that depend on either.  Global visibility,
however, is
>much easier to distinguish than is central control.  Put another way,
any
>control that depends on global knowledge of the state of the system as
>whole, should be considered central control.

It's interesting that you brought this up.  Our group was just talking
about
a related issue yesterday.  Consider the circle model (found in the
Sample Models/
Mathematics folder of the Starlogo 2.0 distribution).  The algorithm
works like this - each turtle knows it's left and right turtle, based
on a total ordering of turtles.  It makes sure to stay a fixed distance
from each of it's two neighbors.  BUT it also chooses a random turtle
from the entire set of turtles, and moves away from that random turtle.

Now, what emerges is a circle.  We could argue that the individual
turtles are using local rules, that they only see their 2 immediate
neighbors, and that they each pick the turtle to repel from in a local
way, BUT these local rules have an underlying global structure!

1. The turtles are totally ordered, and the ring emerges because of this
2. The random repelling is uniformly distributed across the global
population of turtles.  The circle emerges because of this GLOBAL
UNIFORM DISTRIBUTION.  To see this, try putting a curtain down the
middle of the screen, not allowing any turtles to repel from turles on
the other side of the screen.  I'm not sure what you'll get, but I
don't think it will be a circle.

Thoughts?

Larry Latour
UMaine CS Dept.