How to integrate the area below the peak when I dont have function of the peak?

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I wanted to integrate the area below the shaded peak as shown in the image. The plot is taken from an experimental data so I dont have a function of my curve. How can I specify the limit and get the area below the shaded peak? The simple "trapz" function output is showing "NaN" and I understand I am not specifying the limits here. Can someone help me here. thank you.
% Integrate area below the peak
plot(AR_T,AR_mwmg) %AR_T and AR_mwmg are data stored in AR_data.mat file
int_AR = trapz(AR_T,AR_mwmg)

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Accepted Answer

AndresVar on 23 Mar 2022
Edited: AndresVar on 23 Mar 2022
Use conditional indexing to define the limits of extent for the peak.
% remove nan values (why is there a nan at the end?)
idxNotNan = ~isnan(AR_T) & ~isnan(AR_mwmg);
x = AR_T(idxNotNan);
y = AR_mwmg(idxNotNan);
%[pkY, pkX, pkWidth, pkProm]=findpeaks(y,x,'NPeaks',1,'SortStr','descend')
idxPk = x>210 & x<325; % more or less...
xPk = x(idxPk);
yPk = y(idxPk);
hold on;
AreaFull = 0.1168
AreaPk = 0.1166

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