Feigenbaum constant calculation: Difference between revisions

=={{header|Racket}}==

{{trans|C}}

<lang racket>#lang racket

(define (feigenbaum #:max-it (max-it 13) #:max-it-j (max-it-j 10))

(displayln " i d" (current-error-port))

(define-values (_a _a1 d)

(for/fold ((a 1) (a1 0) (d 3.2))

((i (in-range 2 (add1 max-it))))

(let* ((a′ (for/fold ((a (+ a (/ (- a a1) d))))

((j (in-range max-it-j)))

(let-values (([x y] (for/fold ((x 0) (y 0))

((k (expt 2 i)))

(values (- a (* x x))

(- 1 (* 2 y x))))))

(- a (/ x y)))))

(d′ (/ (- a a1) (- a′ a))))

(eprintf "~a ~a\n" (~a i #:width 2) (real->decimal-string d′ 8))

(values a′ a d′))))

d)

(module+ main

(feigenbaum))</lang>

{{out}}

<pre> i d

2 3.21851142

3 4.38567760

4 4.60094928

5 4.65513050

6 4.66611195

7 4.66854858

8 4.66906066

9 4.66917155

10 4.66919515

11 4.66920026

12 4.66920098

13 4.66920537

4.669205372040318</pre>