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How to calculate the area under the curve with data given on an excel file, and not using the function "trapz"?

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Create a MATLAB program to calculate the area under the curve for the strain-stress. The goal of the project is to have a MATLAB script that automatically reads the experimental data set. The MATLAB script must not use native functions like “trapz” in the calculation of the area. The goal is to calculate the area under the stress-strain curve.
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Accepted Answer

Scott MacKenzie
Scott MacKenzie on 3 Aug 2021
Edited: Scott MacKenzie on 3 Aug 2021
f = 'https://www.mathworks.com/matlabcentral/answers/uploaded_files/702117/Steel6150Tens.csv';
T = readtable(f);
T(end,:) = []; % remove last row, outlier
x = T.Strain;
y = T.Stress;
plot(x,y)
% compute area the hard way
a0 = 0;
for i=2:length(x)
a0 = a0 + (x(i)-x(i-1)) * (y(i)+y(i-1))/2;
end
fprintf('Area: %f\n', a0);
Area: 163.079188
% verify result using trapz
a1 = trapz(x, y);
fprintf('Area using trapz: %f\n', a1);
Area using trapz: 163.079188
  8 Comments
Wan Ji
Wan Ji on 10 Aug 2021
By using 'type trapz' command, one can see the vectorized trapz method, the code is simplified as:
z = diff(x,1,1).' * (y(1:end-1,:) + y(2:end,:))/2;

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