NetLogo nothing named SCREEN-SIZE-X has been defined

Question

i'm new using NetLogo and I'm trying to learn it using the 'Hello World' model found on the net. I'm running NetLogo 5.2 on Mac OS X (Yosemite). When I try to set the turtles randomly, in this way

setxy random screen-size-x random screen-size-y

I get this error: Nothing named SCREEN-SIZE-X has been defined

screen-size-x appears in capitalization and so i get an error on this built-in function. Can anyone help me? Thank you

This is the NetLogo code I'm using:

globals [buttons]           ; Global variables

to setup                    ; Initializes model for new run.
    set-default-shape turtles "circle" ; Turtles are circles
    clear-all                          ; Reset turtles and patches
    set buttons 500                    ; Set number of buttons to 500
    create-turtles (buttons)           ; Create "buttons" number of turtles
    ask turtles [setup-turtles]        ; Initialize each turtle
end

to setup-turtles            ; Called for each turtle during setup
    setxy random screen-size-x random screen-size-y ; Set our x,y randomly
end

Answer 1

I think screen-size-x and screen-size-y are NetLogo history. You can use max-pxcor, max-pycor and min-pxcor, min-pycor to get the world borders or world-width and world-height to get just the size.

To get a random position there are random-xcor and random-ycor.

to setup-turtles  
  setxy random-xcor random-ycor
end