solve.scm

solve.scm

(define (add-streams s1 s2)
  (stream-map + s1 s2))

(define (scale-stream stream factor)
  (stream-map (lambda (x) (* x factor)) stream))

(define (integral delayed-integrand initial-value dt)
  (define int
    (cons-stream initial-value
                 (let ((integrand (force delayed-integrand)))
                   (add-streams (scale-stream integrand dt)
                                int))))
  int)

; (define (solve f y0 dt)
;   (define y (integral dy y0 dt))
;   (define dy (stream-map f y))
;   y)

(define (solve f y0 dt)
  (define y (integral (delay dy) y0 dt))
  (define dy (stream-map f y))
  y)


(stream-ref (solve (lambda (y) y) 1 0.001) 1000)