How to find the locations or indices of lower and upper ends of FWHM of a peak
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Vinay Killamsetty
on 14 Jul 2021
Commented: Simon Chan
on 14 Jul 2021
How to find the locations and Index of lower and upper limit of FWHM of the largest peak shown in the pic below
Whn I use findpeaks function I am able to get the FWHM but I find it hard to get the location/index of the upper and lower limits of the FWHM
since there exists another peak in the range having a peak value above the half maximum of the main peak.
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/684023/image.jpeg)
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Accepted Answer
Simon Chan
on 14 Jul 2021
Edited: Simon Chan
on 14 Jul 2021
Suppose y is the data, try this:
You may change the interpolation method, mine is only an example.
The location of the limits on the left side is between idx1 & idx1+1,
while on the right side, it is between idx2-1 & idx2.
[~,location] = max(y);
yn = y/max(y); % Normalized data
idx1 = location - find(diff(yn(location:-1:1)>0.5)~=0,1,'first');
idx2 = location + find(diff(yn(location:1:end)>0.5)~=0,1,'first');
xaxis_left = interp1([yn(idx1), yn(idx1+1)], [x(idx1), x(idx1+1)], [yn(idx1), 0.5, yn(idx1+1)], 'linear');
xaxis_right = interp1([yn(idx2-1), yn(idx2)], [x(idx2-1), x(idx2)], [yn(idx2-1), 0.5, yn(idx2)], 'linear');
FWHM = xaxis_right(2) - xaxis_left(2)
2 Comments
Simon Chan
on 14 Jul 2021
Try this:
idx3 and idx4 are the minimum points on the left and right side respectively.
Hope it helps
idx3 = location - find(diff(yn(location:-1:1))>0,1,'first') + 1;
idx4 = location + find(diff(yn(location:1:end))>0,1,'first') - 1;
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