turtles-own [
	next-turtle	; the next turtle in line (by who number)
        prev-turtle	; the previous turtle in line (by who number)
       	heading-1 	; heading to take to face next-turtle
        dist-1		; a distance away from next-turtle
        heading-2 	; heading to take to face prev-turtle
        dist-2 		; a distance away from prev-turtle
        repel-turtle	; which turtle to repel from
]


;; setup procedure
;; called by the observer setup procedure
;; Sets the turtle's color to red, sets a random heading and
;; moves forward 25 steps.  Sets turtle parameters prev and next
to setup
	setc red
	seth random 360
	fd random 25
	setnext-turtle who + 1
	if next-turtle >= total-turtles [setnext-turtle 0]
	setprev-turtle who - 1
	if prev-turtle < 0 [setprev-turtle total-turtles - 1]
end

;; adjust procedure
;; called by adjust button
;; Computes heading and distance to prev-turtle and next-turtle
;; Moves between prev and next turtle using the heading and distance information
;;
to adjust
	setheading-1 towards xcor-of next-turtle ycor-of next-turtle
	setdist-1
  		(convergence / 100) *
     		((distance xcor-of next-turtle ycor-of next-turtle)
         	 - desired-distance)

	setheading-2 towards xcor-of prev-turtle ycor-of prev-turtle
	setdist-2
  		(convergence / 100) *
  		((distance xcor-of prev-turtle ycor-of prev-turtle)
           	- desired-distance)

	seth heading-1
	fd dist-1
	seth heading-2
	fd dist-2
end


;; repel procedure
;; called by repel button
;; Selects a random turtle to repel away from, sets heading to face this
;; turtle then backs up some amount derived using the user-defined var
;; repel-strength
;;
to repel
	setrepel-turtle random total-turtles
	seth towards xcor-of repel-turtle ycor-of repel-turtle
	bk repel-strength / 100
end