SICP_2.12-2.16(部分习题)

(require "sicp_2.7-2.11.rkt")
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;2.12
(define (make-center-width c w)
  (make-interval (- c w) (+ c w)))

(define (make-center-percent c p)
  (let ((width (* c (/ p 100))))
    (make-interval (- c width) (+ c width))))

(define (center i)
  (/ (+ (lower-bound i) (upper-bound i)) 2))

(define (percent i)
  (* 100 (abs (/ (width-interval i) (center i)))))

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;2.14
(define (par1 r1 r2)
  (div-interval (mul-interval r1 r2)
                (add-interval r1 r2)))

(define (par2 r1 r2)
  (let ((one (make-interval 1 1)))
    (div-interval one
                  (add-interval (div-interval one r1)
                                (div-interval one r2)))))

(define inter1 (make-center-percent 2 50))
(define inter2 (make-center-percent 4 50))
(define A (make-center-percent 2 0.0004))
(define B (make-center-percent 4 0.0004))

(par1 inter1 inter2)
(par2 inter1 inter2)

(div-interval A B)
(div-interval A A)