SICP 1.3.4 牛顿法

(define (deriv g)  (lambda (x)    (/ (- (g (+ x dx)) (g x))       dx)))(define dx 0.00001)(define (newton-transform g)  (lambda (x)    (- x (/ (g x) ((deriv g) x)))))(define (newtons-method g guess)  (fixed-point (newton-transform g) guess))(define tolerance 0.00001)(define (fixed-point f first-guess)  (define (close-enough? v1 v2)    (< (abs (- v1 v2)) tolerance))  (define (try guess)    (let ((next (f guess)))      (if (close-enough? guess next)        next        (try next))))  (try first-guess))(define (sqrt-a x)  (newtons-method (lambda (y) (- (square y) x)) 1.0))(sqrt-a 2.0)