# Thread: Identify a Sine-Like Curve

1. ## 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.

2. ## 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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3. ## Re: Identify a Sine-Like Curve

Originally Posted by zzephod
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,
$\displaystyle \phi = -2 \pi \lambda$ or
$\displaystyle \lambda = - \phi /(2 \pi)$

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.