I try to make a bunch of turtles (Movers) to go trough a gate and avoid the wall which is white. Somehow the model freezes after a few runs. Go button stays black and blue circle turns for ever. No error MSG given. It must get stuck in some calculation within the "move-movers" function but I can't determine why.
I added a simplified version of my code which still produces the crash. Copy & paste to run. Disable world wrap. Include a slider for "num-movers" Variable.
breed [ movers mover ]
movers-own [ steps ] ; Steps will be used to determine if an agent has moved.
to setup
clear-all
reset-ticks
ask patches [ set pcolor green ]
basic-pattern
end
to basic-pattern ; sets up gate and wall
let wallXCor 16 ; sets a white line to determine the inside & outside of the gate
repeat 33 [
ask patch wallXCor 0 [ set pcolor white ]
set wallXCor wallXCor - 1
]
ask patches with [ pycor > 0 ] [ set pcolor lime ] ; sets the outside of the gate to another color (lime)
; changes color of the center to lime to create a passable opening
ask patch 0 0 [ set pcolor lime ]
ask patch 1 0 [ set pcolor lime ]
ask patch -1 0 [ set pcolor lime ]
end
to distribute-agents ; Distributes the Movers outside the gate based on the patch color lime. The number needs to be set via slider "num-movers"
repeat num-movers [
ask one-of patches with [ pcolor = lime and pycor > 2 and any? turtles-here = false ] [
sprout-movers 1 [ set color red set shape "circle" facexy 0 -12 ] set num-movers num-movers- 1 ]
] end
to go
move-movers
tick
end
to move-movers ; reset the steps variable and facing
ask movers [ set steps steps + 1 ]
ask movers [ facexy 0 -3 ]
; following lines checks if next patch to be steped upon is "legal".
while [ any? movers with [ steps > 0 ] ] [
ask movers with [ steps > 0 ] [
ifelse is-patch? patch-ahead 1
and not any? turtles-on patch-ahead 1
and [ not member? pcolor [ white brown ] ] of patch-ahead 1
[
fd 1
set steps steps - 1
] [ dirchange ]
]
]
end
to dirchange ;If not able to move to next patch change direction to allow a step backwards.
if ( pxcor <= 0 and ycor >= 0 ) [ facexy 1 3 ] ;fd 1 set steps steps - 1]
if ( pxcor >= 0 and ycor >= 0 ) [ facexy -1 3 ] ;fd 1 set steps steps - 1]
end
You're not getting an error message, because there is no actual error. The code just gets stuck in your while loop.
Did you mean to comment out the fd 1 set steps steps - 1 in your dirchange? My guess is that you have a bunch of turtles that face the same patch (either 1,3 or -1, 3) and get stuck because none of them can move because another turtle is in front of them. And because you only subtract from their steps if they actually move, some of them never get to 0 steps.
While is in general a bad primitive to use for this reason, especially when you have this many conditionals in your move code, making it hard to know what is causing your while loop to not end. is it because your turtles are facing a wall, or because they are at the boundary of the world, or because someone else is blocking their path? You just don't know, and because the code is stuck in a loop, your model view doesn't update so you can't see what is going on.
If you insist on keeping the while, I would at least put in a safeguard: write a turtle reporter that checks if your turtles are able to move and break your while if they can't, or give them a finite number of attempts at moving, rather requiring them to have actually moved.