sicp每日一题[2.12]

Exercise 2.12

Defineaconstructor make-center-percent that takes a center and a percentage tolerance and produces the desired interval. You must also define a selector percent that produces the percentage tolerance for a given interval. The center selector is the same as the one shown above.

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我以为这是上道题的要求，已经实现了。。

; 把 w 改为百分比形式
(define (make-center-width c w)
  (let ((tolerance (* c w)))
    (make-interval (- c tolerance) (+ c tolerance))))

(define (center i)
  (average (lower-bound i) (upper-bound i)))

(define (percent i)
  (* (/ (/ (- (upper-bound i) (lower-bound i)) 2)
        (center i))
     100))

(define (display-interval-tolerance i) 
  (newline)
  (display (center i))
  (display " ± ")
  (display (percent i))
  (display "%"))

(define a (make-interval 6.12 7.48))
(define b (make-interval 4.465 4.935))


(display-interval-tolerance a)
(display-interval-tolerance b)

; 执行结果
6.800000000000001 ± 10.000000000000002%
4.699999999999999 ± 4.999999999999998%