MATLAB: How to outline a curve

boundscurve fittingcurveshow to plotoutline

Hello.

If I'm trying to plot variables x and y, and the y values vary so much that the curve looks like the following: http://i.stack.imgur.com/4uiNT.png

The only difference is that mine is a single curve of data with a lot of noise. Is there a way I could just plot the upper and the lower curves so I could just look at the boundaries? Do I have to use the findpeak command?

Thank you for your time!

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This could be also helpful

http://www.mathworks.com/matlabcentral/fileexchange/38841-matlab-implementation-of-harmonic-analysis-of-time-series--hants-

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MATLAB: Plot a smooth envelope for oscillation curves

Do you have a particular selection criteria for the peaks or formula for how you would like the smoothing performed at the extremities?

I ran a spectrogram on your signal to see if there was a simple envelope to extract. It appears that there is, so maybe you could try to extract the amplitude ridges. (It seems a little bit of aliasing is in your sampled signal as well. Not sure if it's important, but have a look)

spectrogram(y,kaiser(256,40),250,[],1/mean(diff(x)),'power','yaxis')

I tried to extract a few ridges:

[sst,f] = fsst(y,1/mean(diff(x)),kaiser(256,10));
fridge = tfridge(sst,f,10,'NumRidges',6);
plot(x,fridge)

I got a reasonable hit on the fundamental, so perhaps you could attempt to extract the spectrum amplitudes along those frequencies to get a good sense of the power envelope.

MATLAB: Interpolating random values to smoothen a curve

you can implement the stavisky golay filter

basically the idea is to iterate through the data and on each point perform a polynomial fit on a window of several data points arround it, then each point is reoplaced with the value of the polynomial fit in that same point.

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MATLAB: Plot a smooth envelope for oscillation curves

MATLAB: Interpolating random values to smoothen a curve

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