; square roots
(define (bisect n)
(let loop ((lo (if (< 1 n) 1. n)) (hi (if (< 1 n) n 1.)))
(display lo) (display " ") (display hi) (newline)
(let ((mid (/ (+ lo hi) 2)))
(cond ((< (abs (- (/ (* mid mid) n) 1)) 1e-14) mid)
((< (* mid mid) n) (loop mid hi))
(else (loop lo mid))))))
(define (heron n) ; x' = (x + (n/x)) / 2
(let loop ((x 1.))
(display x) (newline)
(let ((x-prime (/ (+ x (/ n x)) 2)))
(if (< (abs (- (/ (* x x-prime) n) 1)) 1e-14)
(/ (+ x x-prime) 2)
(loop x-prime)))))
(define (newton n) ; x' = x - (x^2 - n) / 2x
(let loop ((x 1.))
(display x) (newline)
(let ((x-prime (- x (/ (- (* x x) n) (+ x x)))))
(if (< (abs (- (/ (* x x-prime) n) 1)) 1e-14)
(/ (+ x x-prime) 2)
(loop x-prime)))))
(define (optimize n) ; using heron's method
(if (< n 1) (* 1/2 (optimize (* n 4)))
(if (<= 4 n) (* 2 (optimize (/ n 4)))
(let ((x (/ (+ 1. n) 2)))
(let ((x (/ (+ x (/ n x)) 2)))
(let ((x (/ (+ x (/ n x)) 2)))
(let ((x (/ (+ x (/ n x)) 2)))
(let ((x (/ (+ x (/ n x)) 2)))
(let ((x (/ (+ x (/ n x)) 2)))
x)))))))))
(display (bisect 125348)) (newline) (newline)
(display (bisect 0.8)) (newline) (newline)
(display (heron 125348)) (newline) (newline)
(display (heron 0.8)) (newline) (newline)
(display (newton 125348)) (newline) (newline)
(display (newton 0.8)) (newline) (newline)
(display (optimize 125348)) (newline) (newline)
(display (optimize 0.8)) (newline) (newline)