87 lines
2.5 KiB
Scheme
87 lines
2.5 KiB
Scheme
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(load "util.scm")
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(define (integral integrand initial-value dt)
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(define int
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(cons-stream initial-value
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(add-streams (scale-stream integrand dt)
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int)))
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int)
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(display "\nex-3.73 - RC\n")
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(define (RC R C dt)
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(define (rc-proc i v0)
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(add-streams
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(scale-stream i R)
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(integral (scale-stream i (/ 1 C)) v0 dt)))
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rc-proc)
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(define RC1 (RC 5 1 0.5))
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(assert (take 5 (RC1 ones 4.2))
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'(9.2 9.7 10.2 10.7 11.2))
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(display "\nex-3.74 - zero-crossings\n")
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(define sense-data
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(list->stream
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'(1 2 1.5 1 0.5 -0.1 -2 -3 -2 -0.5 0.2 3 4)))
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(define response '(0 0 0 0 0 -1 0 0 0 0 1 0))
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(define (sign-change-detector s2 s1)
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(cond
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((and (< s1 0) (>= s2 0)) 1)
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((and (>= s1 0) (< s2 0)) -1)
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(else 0)))
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(define (make-zero-crossings input-stream last-value)
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(cons-stream
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(sign-change-detector (stream-car input-stream) last-value)
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(make-zero-crossings (stream-cdr input-stream)
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(stream-car input-stream))))
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(define zero-crossings (make-zero-crossings sense-data 0))
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(assert (take 12 zero-crossings) response)
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(define zero-crossings
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(stream-map sign-change-detector
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sense-data
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(cons-stream 0 sense-data)))
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(assert (take 12 zero-crossings) response)
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(display "\nex-3.75 - averaged zero-crossings\n")
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; Louis' solution uses the average value as last-value which means that the new
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; value and the previous average are used for averaging and not simply two
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; consecutive values as proposed by Alyssa.
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(define (make-zero-crossings-avg input-stream last-value last-avpt)
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(let ((avpt (/ (+ (stream-car input-stream) last-value) 2)))
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(cons-stream (sign-change-detector avpt last-avpt)
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(make-zero-crossings-avg (stream-cdr input-stream)
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(stream-car input-stream)
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avpt))))
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(display (take 12 (make-zero-crossings-avg sense-data 0 0))) (newline)
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(display "\nex-3.76 - smooth zero-crossings\n")
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(define (smooth xs)
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(stream-map average xs (stream-cdr xs)))
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(define (make-zero-crossings-smoothed input-stream last-value)
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(make-zero-crossings (smooth input-stream) last-value))
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(assert (take 11 (make-zero-crossings-smoothed sense-data 0))
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'(0 0 0 0 0 -1 0 0 0 0 1))
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(display "\nex-3.77\n")
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;(display "\nex-3.78\n")
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;(display "\nex-3.79\n")
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;(display "\nex-3.80\n")
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;(display "\nex-3.81\n")
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;(display "\nex-3.82\n")
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