MATLAB: Calculation of a given area using the trapz

MATLABNumerical Integration and Differentiationtrapz

Hello, to calculate the total area I used the trapz and it worked, but I can't do it for a certain area (figure above inside the red rectangle). If you can calculate, do I use trapz or do I use another? Show me how you do, please.
Thanks

Best Answer

You need to limit the range of x and y that are fed to trapz, you could do something like this, assuming your original variables are called x and y (modify accordingly for your actual variable names)
% assume x and y are defined earlier
% define range of interest
xRange = [21,31.3]
% find logical indices for range of interest
idl = x >= xRange(1) & x <= xRange(2);
% provide just values of interest to trapz
A = trapz(x(idl),y(idl))
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