version 0.3
The applet shows part of an infinite square grid. Each cell in the grid has a rotor which can point in one of four directions. Initially the directions of the rotors circulate clockwise around the origin.
A bug traverses this grid by following the direction of the rotor. The rotor on a cell will rotate 90° as soon as it lands in the cell. In each step of the system, the rotor at the cell occupied by the bug rotates and the bug takes a step in the indicated direction.
There is a source at (0,0) (shown as a square with a white border) and a sink at (1,1) (shown as a solid black square). In each stage, the bug starts at the source, and takes a walk following the instructions given by successive rotors, until it either arrives at the sink (at which point it hops back to the source) or it arrives at the source; either way, the stage is over, and a new stage start.
The applet keeps track of how many times the bug arrives at the source (by walking from one of the four cells adjoining the source, not by hopping from the sink) and how many times the bug arrives on the sink.
The location of the bug is indicated by a square superimposed with the cell occupied by the bug.
What the colors mean:
The paused/unpaused button controls the automatic evolution of the system. Press the pause button to start and stop the system.
The faster/slower buttons control the speed of the system by changing the interval that the applet waits between calculations.
Press the restart button to restart the system.
If you press the skip stages button, you will get a dialog asking how many stages you would like to skip each turn. If you enter 0, no stages will be skipped and each step will be shown. If you enter 1, then the applet will show each stage, but no intervening steps. If you enter n, an integer greater than 1, the applet will only show every nth stage.
Use the zoom in/zoom out buttons to zoom in on detail in the system. Use the scrollbars to look around. For best results, pause the applet before zooming in and zoom out before unpausing.
While the applet is paused, hit the next stage button to show the next stage.
While the applet is paused, hit the next step button to show the next step.
Press the score button to see some statistics about the number of captures at the sink and the source.
The Two-Dimensional Rotor-Walk Applet is Copyright (C) 2003 Hal Canary, University of Wisconsin-Madison.
This work was supported by the University of Wisconsin.
The Two-Dimensional Rotor-Walk Applet comes with ABSOLUTELY NO WARRANTY. This program is free software; you can redistribute it and/or modify it under the terms of version 2 of the GNU General Public License as published by the Free Software Foundation.