# how to superimpose peak intensities

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Kun Yan on 18 Mar 2021
How to superimpose the peak intensities of multiple peaks in the spectrum to obtain an envelope?
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### Answers (1)

Alamanda Ponappa Poovaya on 23 Mar 2021
Edited: Alamanda Ponappa Poovaya on 23 Mar 2021
I understand that you want to find an envelope for all the peak values of different curves. Looking at the image you shared, I assume each curve only has one peak value.
First, you can obtain the location and height of all your peaks and store them in an array.
For example:
[peakYCoords(1),peakXCoords(1)] = findpeaks(y,x);
Say all your peak values are in vector peakYCoords and their corresponding locations are in vector peakXCoords, you can use polyfit and polyval functions to fit a curve to these points, which would act as an envelope
Choose the value of n depending on the number of curves. See the documentation for polyfit for more details.
p = polyfit(peakXCoords, peakYCoords, n);
v = polyval(p, t);
plot(t, v)
Another alternative is to use the envelope function
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