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getting the area under the peaks

Asked by Rashid Hussein on 18 Nov 2017
Latest activity Commented on by Star Strider
on 19 Nov 2017
I have a graph that contain many peaks , but I want to get the sum( area under peak) of counts (y-axis) in every peaks as shown in the image that I uploaded , thanks in advanced

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1 Answer

Answer by Star Strider
on 18 Nov 2017
 Accepted Answer

I would first identify the low points (‘valleys’) by inverting your signal and then using the Signal Processing Toolbox findpeaks function to locate them. Then integrate between those points to identify the peaks.
Example
t = linspace(0, 10*pi, 250); % Create Data
s = sin(t) + 0.2*cos(5*t) + 2; % Create Data
figure(1)
plot(t, -s)
grid
[Vlys, Idx] = findpeaks(-s, 'MinPeakHeight',-1.1);
Area = cumtrapz(t,s);
idxvct = [1 Idx length(s)];
for k1 = 1:length(idxvct)-1
PkAreas(k1) = Area(idxvct(k1+1)) - Area(idxvct(k1));
end
The ‘PkAreas’ vector will have the areas of the peaks.
You will have to adapt this to your data. Be sure to plot the negative of your data first so you can see and set the appropriate arguments for findpeaks.

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Star Strider
on 19 Nov 2017
My pleasure.
My code creates the cumulative integral, identifies the valleys, then uses those indices to separate and calculate the areas for each peak in the ‘PkAreas’ vector.
My code worked correctly with the data I created to test it, because I do not have your data to test it with. You have included my code, although you commented it out.

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