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
AndresVar on 23 Mar 2022
Edited: AndresVar on 23 Mar 2022
Use conditional indexing to define the limits of extent for the peak.
clear
load("AR_data.mat")
% 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);
%findpeaks(y,x,'Annotate','extents','WidthReference','halfheight','NPeaks',1,'SortStr','descend');
%[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);
figure;
plot(x,y,LineWidth=2,DisplayName='data')
hold on;
plot(xPk,yPk,'--',LineWidth=2,DisplayName='peak')
legend('show');
AreaFull=trapz(x,y)
AreaFull = 0.1168
AreaPk=trapz(xPk,yPk)
AreaPk = 0.1166

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