改进good-enough
监视猜测值在从一次迭代到下一次迭代的变化情况,当改变值相对于猜测值的比率很小时就结束。
#lang sicp
(define (sqrt-iter guess x)
(if (good-enough? guess x)
guess
(sqrt-iter (improve guess x)
x)))
(define (improve guess x)
(average guess (/ x guess)))
(define (average x y)
(/ (+ x y) 2))
(define (good-enough? guess x)
(< (abs (- (improve guess x) guess))
.001))
(define (abs x)
(if (> x 0)
x
(- x)))
(define (square x)
(* x x))
(define (sqrt x)
(sqrt-iter 1.5 x))