Emergence 2009: Langton's Ant II

This model more-or-less follows the basic Langtan's Ant procedure. Differences are:

-Turtles move two steps instead of one.

-Turtles do not respond to patch color, but another patch variable called 'state,' which can be either on or off.

-Since turtles do not affect patchc color, potion can be tracked as a drawing, which shows the complete patch of the turtle and does not affect the patch of other turtles.

-When the number of patches a turtle has visited reaches the observer-defined 'reset-point,' the model runs a 'safe-setup' procedure. This is much like 'setep' but does not clear-all, so drawings and some variables are conserved. Also, the heading at which the turtle starts is increased by 30 degrees at each reset.

-The 'Finish & Center' button allows a turtle, once stopped, to complete its path until it reaches the reset-point, at which time it picks up its pen and jumps to the origin (useful between direction changes).

SETUP works as usual.

FORWARD runs like a basic Langton's Ant except with setps of length 2.

REVERSE is like FORWARD but turtles move back and rules are reversed.

ANGLE lets the observer set the initial heading.

FINISH & CENTER works as described above and can be used between changes of direction (mainly for aesthetic purposes).

RESET causes the model to do a safe-setup after a number of patch visits defined by the user in the RESET-POINT input box.

RESET-POINT can be any number, but I suggest something between 1500 and 2000.

The inspiration for this model came from noticing that with a turtle that moves forward two steps instead of 1, you still get something that looks basically like Langton's Ant. More interestingly, you get the same behavior witht he heading set to any multiple of 30 (which is not true for the 1-step version).

Because the model uses a pen to trace turtle motion, you are seeing the complete patch of the turtle.

Also note the 'while' loops in the 'center' procedure, and the conditions in 'go' and 'go-back' which keep the loops from being infinite.

When the RESET is on, watch how the 'angle' slider moves by itself.