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Thread: Identify a Sine-Like Curve

  1. #1
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    Identify a Sine-Like Curve

    I have created some data numerically and plotted it.
    It looks like a sine wave that has been scaled down and with a period of 1.
    However, comparing it to a function of the form y = K1 * sin(2 * PI * x), indicates that this proposed function is NOT a fit.
    Simply translating a sine curve vertically or horizontally doesn't work.

    It looks like a Pringle potato chip that is being viewed from the side.

    I have attached a screen capture of the plot.

    Any suggestions as to what kind of function would describe this plot?
    All help is much appreciated.


    Identify a Sine-Like Curve-asech_capture.png
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  2. #2
    Senior Member zzephod's Avatar
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    Re: Identify a Sine-Like Curve

    Try an off-set chirp:

    $$y=K_1\sin( \omega x(1+\lambda x)+\phi)+C$$

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    Re: Identify a Sine-Like Curve

    Quote Originally Posted by zzephod View Post
    Try an off-set chirp:

    $$y=K_1\sin( \omega x(1+\lambda x)+\phi)+C$$
    Hi, "zzephod".

    Thanks for that information.
    I had never heard of a chirp before.

    Doing a couple searches, I found some information about chirps.
    Chirps seem to change frequency, but not magnitude, or am I misunderstanding the concept?

    I will work with it a little and see where it takes me.

    Since the curve is 0 at x = 0, C = 0.
    Since the curve is 0 at x = 1,
    \phi = -2 \pi \lambda or
    \lambda  = - \phi /(2 \pi)

    Now I need to use one more point to find phi and lambda.
    Since the curve reaches a larger maximum (~ 0.008) than it does a minimum (~ -0.003), it looks like a simple constant might not work.
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