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; frac objects are like (number 'numerator 'denominator)
; the classics; just yanked from wikipedia w/o errors or citation
(define cgs-units-constants
(list
(list (* 2.998 (expt 10 10)) 'c) ; speed of light
(list (* 6.626 (expt 10 -27)) 'h) ; plank
(list (* 4.803 (expt 10 -10)) 'e) ; electron charge (esu)
; (list 3.14159268 'pi) ; pi!
))
(define (make-ordered-fracs primatives)
(sort (append primatives
(map (lambda (x)
(list (/ 1 (car x)) (quasiquote '(/ 1 ,(cadr x)))))
primatives))
(lambda (a b) (< (car a) (car b)))))
(make-ordered-fracs cgs-units-constants)
(define (good-approximation x primatives eta)
(define (closest-term y ordered)
(cond ((null? ordered) (error "need at least one thing to check!"))
((null? (cdr ordered)) (car ordered))
((< (abs (- y (caar ordered)))
(abs (- y (caar (cdr ordered)))))
(car ordered))
(else (closest-term y (cdr ordered)))))
(define (iterate-term y ordered eta)
(if (< (abs y) (abs eta))
(begin
(display y)
(newline)
(display (- y eta))
'())
(begin
(display "x: ") (display y) (newline)
(let ((best (closest-term y ordered)))
(cons (cadr best)
(iterate-term (/ y (car best)) ordered eta))))))
(iterate-term x (make-ordered-fracs primatives) eta))
(good-approximation 876259081724391234.0 cgs-units-constants 200.)
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