NetLogo User Community Models

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Download If clicking does not initiate a download, try right clicking or control clicking and choosing "Save" or "Download".(The run link is disabled for this model because it was made in a version prior to NetLogo 6.0, which NetLogo Web requires.)

WHAT IS IT?

A simple model. A chain of linked turtles. They follow each other. That is, each link as a "leader". Each link steps toward its leader, until it is some minimum distance, if the leader is too close, the link steps away at a preset angle.

Use the sliders and switches to vary the rules that are used.

Some interesting effects emerge, especially with many links.

Note: the best speed results when the effective link size is 1.0.
so, when scale-with-min-dist is on, min-dist * scale-factor should be 1
other values will be significantly slower.

To effectively use larger chains, don't scale down, rather, increase the
size of the screen, and reduce the pixels-per-patch. By keeping the effective size at 1.0, even very long chains can be effectively used.

The controls:

pop - how many links in the chain. can not be changed during GO.

min-dist - the closest that links want to get
when 'scale-with-min-dist' is on,
size-factor is multiplied by this value.

step-size - how far a link moves each step
smaller values make for smoother movement,
but experiement with larger values too:
interesting effects emerge.

avoid-heading - the angle added to the current heading
when the lead is too close

size-factor - the base size of the links.

scale-with-min-dist - when on, the size is scaled by min-dist.
for links that seem to be connected, turn this on,
then set size-factor to 2.

double-correct - after turning away and stepping forward or backward,
turn back by the same amount

shape-choice - choose the shape to use for the chain.
different shapes reveal different information about the chain
- lines show the way angles change
- circle hides the chaning angles, but lets one focus on
the chain as a whole.
- dotted-vector accentuates the curvyness of a shape.

frame-skip - model skips displaying this many frames. speeds things up,
can hide complexity for rapidly evolving shapes,
can use to freeze-frame repeating shapes, and determine the cycles

THINGS TO LOOK FOR

when a link wraps across an edge, the result is usually that the follower turns and crosses the screen to get back to it. this can keep a chain system unstable.

some chain systems will stabilize given enough room and time
some will shrink/expand into a circle
some never calm down
some seem stable for awhile (especially larger chains) then suddenly shift.
note that often the overall *shape* is fairly stable, even though the individual members are racing around and around the perimiter.

NETLOGO FEATURES

* Well chosen shapes can expose information.
* Using nodisplay and display to control screen-redrawing
* Storing turtles in a turtle variable creates linked turtles
* turtle scaling strongly affects execution speed.

COPYRIGHT & LICENSE
This work is Copyright © 2004 James P. Steiner.

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