to setup ca ask patches [ ifelse random 100 < crud-density [ set pcolor black ] [ set pcolor white ] ] cct num-vants [ set heading 90 * random 4 set color red set size 6 ] ;; much easier to see this way end ;; We can't use "ask turtles", because then the vants would ;; execute in a different random order each time. So instead ;; we use SORT to get the turtles in order by who number. to go-forward foreach sort turtles [ ask ? [ fd 1 turn ] ] end to go-reverse foreach reverse sort turtles [ ask ? [ turn bk 1 ] ] end to turn ifelse pcolor = white [ set pcolor black rt 90 ] [ set pcolor white lt 90 ] end ; *** NetLogo 3.1.4 Model Copyright Notice *** ; ; Copyright 2005 by Uri Wilensky. All rights reserved. ; ; Permission to use, modify or redistribute this model is hereby granted, ; provided that both of the following requirements are followed: ; a) this copyright notice is included. ; b) this model will not be redistributed for profit without permission ; from Uri Wilensky. ; Contact Uri Wilensky for appropriate licenses for redistribution for ; profit. ; ; To refer to this model in academic publications, please use: ; Wilensky, U. (2005). NetLogo Vants model. ; http://ccl.northwestern.edu/netlogo/models/Vants. ; Center for Connected Learning and Computer-Based Modeling, ; Northwestern University, Evanston, IL. ; ; In other publications, please use: ; Copyright 2005 Uri Wilensky. All rights reserved. ; See http://ccl.northwestern.edu/netlogo/models/Vants ; for terms of use. ; ; *** End of NetLogo 3.1.4 Model Copyright Notice *** @#$#@#$#@ GRAPHICS-WINDOW 220 10 711 522 240 240 1.0 1 10 1 1 1 0 1 1 1 -240 240 -240 240 CC-WINDOW 5 536 720 631 Command Center 0 BUTTON 47 151 170 184 NIL setup NIL 1 T OBSERVER T NIL BUTTON 67 244 151 277 forward go-forward T 1 T OBSERVER NIL NIL SLIDER 18 38 207 71 num-vants num-vants 1 16 1 1 1 NIL BUTTON 67 278 151 311 reverse go-reverse T 1 T OBSERVER NIL NIL SLIDER 18 77 207 110 crud-density crud-density 0 100 0 1 1 % @#$#@#$#@ WHAT IS IT? ----------- This is a basic virtual ant ("vant") model. It shows how extremely simple deterministic rule can result in very complex-seeming behavior. It also demonstrates the concept of time reversibility and shows that time reversibility is not incompatible with complex behavior. HOW IT WORKS ------------ The world is a grid of patches. Each patch can be either black or white. Initially, they are all white. The rules the "vants" (virtual ants) follow are very simple. Each vant faces north, south, east, or west. At each time step, a vant moves to the next patch. Then it looks at the new patch: - If the new patch is white, the vant colors the patch black and turns right 90 degrees. - If the new patch is black, the vant colors the patch white and turns left 90 degrees. That's it! The world wraps, so when a vant moves off one side of the view it reappears at the other side. HOW TO USE IT ------------- The SETUP button colors all the patches white and creates a number of vants determined by the the NUM-VANTS slider. Pressing the FORWARD button makes the vants start to move according to the normal rules. You can stop the FORWARD button and then press the REVERSE button instead to make the vants move backwards instead of forwards, while still following the same turning rule. The model runs very fast. You may want to use the speed slider (on the top edge of the view) to slow the model down so you see the vants following the rules in slow motion. THINGS TO NOTICE ---------------- To make it easier to see, the vant is shown as larger than a patch. The resulting patterns sometimes have obvious structure, but sometimes appear random, even though the rules are deterministic. Call the diagonal paths that form "highways". Are there different kinds of highways? THINGS TO TRY ------------- Compare the results with one vant to those with multiple vants. Are there any behaviors you get with multiple vants that don't occur with just one? When there are multiple vants, they are initially given random headings. That means that you may get different looking behavior even with the same number of vants, depending on the directions they start out facing. If you press the REVERSE button, the vants turn then move backwards, instead of moving forwards then turning. The turn rule is the same. What effect does this have? Press SETUP, run the model forwards a little, then stop the GO button and press REVERSE instead. EXTENDING THE MODEL ------------------- Without changing the rules, you could change the visualization by making different vants different colors and color-coding the patches to show which vant touched a patch last. This should make some additional structure apparent to the eye. NETLOGO FEATURES ---------------- You can use the SORT primitive to created a list of turtles sorted by who number. That is necessary in this model because we need the turtles to execute in the same order at every tick, rather than a different random order every tick as would happen if we just said "ask turtles". RELATED MODELS -------------- Turing Machine 2D -- similar to Vants, but much more general. This model can be easily configured to use Vants rules, or to use other rules. CREDITS AND REFERENCES ---------------------- The rules for Vants were originally invented by the artificial life researcher Chris Langton. Modified 2007-09-29 by B.J. MacLennan to have a larger world and to allow specifying an initial density of "crud" (black patches), as in Gary William Flake's ants program for "The Computational Beauty of Nature" (MIT Press, 1998). To refer to the original model in academic publications, please use: Wilensky, U. (2005). NetLogo Vants model. http://ccl.northwestern.edu/netlogo/models/Vants. Center for Connected Learning and Computer-Based Modeling, Northwestern University, Evanston, IL. In other publications, please use: Copyright 2005 Uri Wilensky. All rights reserved. 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