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问题:
I'm trying to create a model where turtles walk randomly (but with a tendency for forward movement) until they land on a yellow coloured patch which represents a baited object.
When a turtle lands on one of the yellow patches, I'd like it to stop on that patch and stay there for 15 ticks whilst it 'investigates' the bait.
After 15 ticks have elapsed I want the turtles to continue moving as usual until they encounter another yellow patch.
I've attempted to modify parts of this parked card model in the netlogo modelling commons but couldn't really make sense of it (I'm new to netlogo) http://modelingcommons.org/browse/one_model/3205#model_tabs_browse_procedures
I've also tried implementing a count-down timer as described in this thread How can one create a countdown timer in NetLogo?
However I receive a runtime error 'Only the observer can ASK the set of all turtles' when I try to run the simulation. Can anyone tell me where I'm going wrong? Probably several places! Thanks.
Here's the code that's causing the runtime error:
turtles-own [count-down] to setup clear-all ask patches with [count neighbors != 8] [set pcolor blue] create-turtles 20 ask turtles [setxy random-xcor random-ycor pen-down] ask n-of 20 patches [ set pcolor yellow ] reset-ticks end to go move-turtles tick if ticks >= 720 [stop] end to move-turtles ask turtles [ ifelse pcolor != yellow [continue] [stay] ] end to continue ask turtles [rt -90 + random 181] ask turtles [ifelse [pcolor] of patch-ahead 1 = blue [ lt random-float 360 ] [fd 1] ] end to stay ask turtles [ setup-timer decrement-timer if timer-expired? [continue] ] end to setup-timer set count-down 15 end to decrement-timer set count-down count-down - 1 end to-report timer-expired? report ( count-down
回答1:
This is just one example, How many ticks they should stay in the yellow area? i Assumed 15 ticks and I ask turtles to print their tick number on their label too, if it runs too fast you might miss their stay so adjust running speed for your model to see when they stay and when they move. You can have different methods to continue , in this one they just move 1 patch forward.
turtles-own [count-down] to setup clear-all ask patches with [count neighbors != 8] [set pcolor blue] create-turtles 20 ask turtles [setxy random-xcor random-ycor pen-down set count-down 15 ] ask n-of 20 patches [ set pcolor yellow ] reset-ticks end to go move-turtles tick if ticks >= 720 [stop] end to move-turtles ask turtles [ ifelse pcolor != yellow [continue] [stay] ] end To continue rt random 10 fd 1 end to stay set count-down count-down - 1 ;decrement-timer set label count-down if count-down = 0 [ Continue set label "" reset-count-down ] end to reset-count-down set count-down 15 end
回答2:
To answer just the part about "Only the observer can ASK the set of all turtles", that error message happens if you do:
ask turtles [ ask turtles [ do-something ] ]
This isn't allowed in NetLogo because it's almost always accidental rather than intentional. You probably just wanted each turtle to "do-something" once; you probably didn't mean for each turtle to "do-something" for every possible pair of two turtles.
It's less obvious that you're having all turtles ask all turtles if it's split across procedures. So for example if you write:
to go ask turtles [ my-procedure ] end to my-procedure ask turtles [ do-something ] end
It's still wrong for the same reason, but it isn't as easy to see that just from glancing at it.
Your code follows this latter pattern. You have:
to move-turtles ask turtles [ ... continue ... ] end to continue ask turtles [ rt -90 ... ] end
I don't think you want to do ask turtles in the continue procedure. Since you call the procedure inside ask turtles, it's already a turtle procedure. I'd suggest writing it as:
to continue ;; turtle procedure rt -90 ... end
The comment reminds you that it's intended to be run by turtles. (We follow this style in all of the models in the Models Library.)
