Plotting the cobweb diagram for the logistic equation.

logistic_equation_3.rkt

;;; Plots the cobweb diagram for the given number of steps, parameter r
;;; and starting point x-init.
(define (plot-cobweb-diagram steps r x-init)
  (define (cobweb)
    (let ((endpoints (list (vector x-init 0)))
          (x x-init)
          (y '()))
      (for ((i (in-range 0 steps)))
        (set! y (logistic-equation r x))
        (set! endpoints 
              (cons (vector y y) 
                    (cons (vector x y) endpoints)))
        (set! x y))
      (reverse endpoints)))
  (parameterize ((plot-width 400)
                 (plot-height 400)
                 (plot-font-size 11)
                 (plot-x-label "x")
                 (plot-y-label "y")
                 (line-color 'black))
    (plot
     (list
      (function (lambda (x) (logistic-equation r x)) 0 1)
      (function identity 0 1)
      (lines (cobweb) 
             #:x-min 0 #:x-max 1 #:color 'blue)))))