Can't run Netlogo code - asking turtles to look around themselves and select the lowest patch variable - netlogo

Question

I am trying to get my turtles to look around themselves in netlogo and select a patch with the lowest slope variable in radius 2 - and if there isn't one to just select any patch.
I check my code, and it says everything is fine, but when I run it I keep getting this error: this code can't be run by a patch - error while patch X X running ifelse - called by procedure move - called by procedure go - called by button "go"
This is my move code:
to move
ask turtles [ask patches in-radius 2
[ifelse slope < 5
[fd 1]
[move-to one-of patches in-radius 2]
]
]
end
I have already tried downhill and downhill4 but my agents seemed to get stuck at the bottom of the slope and couldn't move anywhere.
Thank you for any help and advice!
Thank you - my code now works!

Answer 1

Because you are asking turtles to ask patches, the code inside the ask patches is run by the patch! A patch can’t use turtle variables, and doesn’t know that you mean to refer to the variables of the turtle that asked the patch.
This is what “of myself” is for. It lets an agent (self) talk to the agent that is telling it what to do. You’ll see stuff like “set heading [heading] of myself” But that’s not what you need here.
we could use an ask patches like you are doing here, but we really don’t want them to do anything, and it’s going to make the code much more complex looking. Anyway, We just want to find a patch that meets the turtle’s needs and move to it.
So instead. We can query the nearby patches using a WITH and store the set of patches found in a “patch set” variable.
If there are any, we can move to one of them.
Else, we can just move forward.
So
To move
Ask turtles
[
;; here the turtle tells patches to test the patch’s own slope
Let good-spots patches in-radius 2 with [ slope < 5 ]
;; are there some patches that pass the test?
If-else any? Good-spots
[ ;; Yes, pick one and go there
move-to one-of good-spots
]
[ ;; No, just move forward
Fd 1
]
]
End
Edit to add : Matteo’s answer correctly identifies the actual requirement, based on the question: move directly to the flattest patch, versus what the code above does, move to one of the flatter patches, if there is one.
Move-to min-one-of patches in-radius 2 [ slope ]
As you noted, This is similar but not identical to
Downhill slope
And neither of these may prevent turtles from getting stuck in a pit. You may need more code to detect pits and jump out of them.

Answer 2

The problem is not about variables but about commands: you are asking patches to run forward or to run move-to, while these are turtles' commands.
Now, for the purpose of the question, there is another issue: you said that you want
turtles to look around themselves in netlogo and select a patch with the lowest slope variable in radius 2 - and if there isn't one to just select any patch
However, even if we ignore the problem about asking patches to run forward or move-to, the structure of your code implies something very different. Your code seems to intend:
Turtles, check if there are any nearby patches with slope lower than a specific threshold;
If there are, move forward in whatever direction you are already facing;
If there are not, move to a random nearby patch.
The solution below is based on the assumption that what you want is what you said, and not what your code seems to imply.
The solution is very simple and only needs min-one-of (check it here):
to move
ask turtles [
move-to min-one-of patches in-radius 2 [slope]
]
end
As a demonstration, consider this full example:
patches-own [
slope
]
to setup
clear-all
ask patches [
set slope random 10 + 5
set pcolor scale-color green slope 5 14
]
create-turtles 10 [
setxy random-xcor random-ycor
set color yellow
]
end
to go
ask turtles [
move-to min-one-of patches in-radius 2 [slope]
]
end
You will see that turtles tend to go to darker patches, that are those with lower slope.