sicp习题试解 (1.8)

; ======================================================================

;

; Structure and Interpretation of Computer Programs

; (trial answer to excercises)

;

; 计算机程序的构造和解释(习题试解)

;

; created: code17 02/24/05

; modified:

; (保持内容完整不变前提下，可以任意转载)

; ======================================================================

;; SICP No.1.8

;; 只需要替换No.1.7中的improve函数算法即可

(define (improve guess x)

(/ (+ (/ x

(* guess guess))

(* 2 guess))

3))

(define (good-enough? oldguess guess)

(< (abs (/ (- guess oldguess)

guess))

0.001))

(define (cube-iter oldguess guess x)

(if (good-enough? oldguess guess)

guess

(cube-iter guess

(improve guess x)

x)))

(define (cube-root x)

(cube-iter 0.0 1.0 x))

;; Test-it:

;; Welcome to MzScheme version 209, Copyright (c) 2004 PLT Scheme, Inc.

;; > (cube-root 0)

;; 4.9406564584125e-324

;; > (cube-root 125)

;; 5.000000000287929

;; > (cube-root 1000)

;; 10.000000145265767

;; > (cube-root -27)

;; -3.000000005383821

;; >