SICP 1.3.3 二分法作为方程的根

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这次所犯的错误是abs函数括号闭合错了，不懂得怎么调Bug，有点烦。

(define (search f neg-point pos-point)  (let ((mid-point (average neg-point pos-point)))    (if (close-enough? neg-point pos-point)      mid-point      (let ((test-value (f mid-point)))        (cond ((positive? test-value) (search f neg-point mid-point))              ((negative? test-value) (search f mid-point pos-point))              (else mid-point))))))(define (close-enough? x y)  (< (abs (- x y)) 0.001))(define (average x y)  (/ (+ x y) 2))(define (half-interval-method f a b)  (let ((a-value (f a))        (b-value (f b)))    (cond ((and (negative? a-value) (positive? b-value))            (search f a b))          ((and (negative? b-value) (positive? a-value))           (search f b a))          (else             (error "Values are not of opposite sign" a b)))))(newline)(display (half-interval-method sin 2.0 4.0))(newline)(display (half-interval-method (lambda (x) (- (* x x x) (* 2 x) 3))                               1.0                               2.0))(newline)(display (half-interval-method sin 2.0 3.0))

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