SICPゼミ第30回

練習問題3.73

(define (RC R C dt)
  (define (calc i v0)
    (add-streams (scale-stream i R) (integral (scale-stream i (/ 1 C)) v0 dt)))
  calc)

民主主義しゅき〜〜（ドナルド・トランプ）

練習問題3.74

(define (sign-change-detector now last)
  (if (> (* now last) 0)
      0
      (if (= last 0)
          (if (>= now 0) 0 -1)
          (if (< last 0) 1 0))))
              

(define zero-crossings
  (stream-map sign-change-detector
              sense-data
              (cons-stream 0 sense-data)))

練習問題3.75

(define (make-zero-crossings input-stream last-value last-average)
  (let ((avpt (/ (+ (stream-car input-stream)
    last-value)
    2)))
  (cons-stream
    (sign-change-detector avpt last-average)
    (make-zero-crossings
      (stream-cdr input-stream) (stream-car input-stream) avpt))))

by dolicas

練習問題3.76

(define (smooth input-stream)
  (cons-stream (/ (+ (stream-car input-stream)
                     (stream-car (stream-cdr input-stream)))
                  2)
               (smooth (stream-cdr input-stream))))