Exercise 1.8.  Newton's method for cube roots is based on the fact that if y is an approximation to
          the cube root of x, then a better approximation is given by the value
          (x/y2+2y)/3
          Use this formula to implement a cube-root procedure analogous to the square-root procedure. (In
          section 1.3.4 we will see how to implement Newton's method in general as an abstraction of these
          square-root and cube-root procedures.)

          (define (cube x)
            (* x x x))
          (define (square x)
            (* x x ))
          (define (result x y)
           (/ (+ (/ x (square y)) (* 2 y)) 3))
          (define (improve  x guess)
            (result   x guess))
          (define (good-enough?  x guess)
            (< (abs (- (* guess guess guess ) x))0.001))
          (define (sqrt-iter x  guess)
            (if (good-enough?  x guess)
                guess
                (sqrt-iter x (improve  x guess)
                           )))
          posted on 2009-03-06 16:22 lzj520 閱讀(276) 評(píng)論(0)  編輯  收藏 所屬分類: 個(gè)人學(xué)習(xí)日記sicp
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