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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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Andres Gustavo Ambriz Gudiel 2021-8-3

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https://ww2.mathworks.cn/matlabcentral/answers/891742-how-to-calculate-the-area-under-the-curve-with-data-given-on-an-excel-file-and-not-using-the-functi

评论： Wan Ji 2021-8-10

采纳的回答： Scott MacKenzie

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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James Tursa 2021-8-3

I meant are you supposed to write your own area calculator function from scratch? (be it Euler or trapezoid or whatever)

Andres Gustavo Ambriz Gudiel 2021-8-3

Yes, indeed. Everything from scratch. Thank you.

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采纳的回答

Scott MacKenzie 2021-8-3

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https://ww2.mathworks.cn/matlabcentral/answers/891742-how-to-calculate-the-area-under-the-curve-with-data-given-on-an-excel-file-and-not-using-the-functi#answer_760132

编辑：Scott MacKenzie 2021-8-3

在 MATLAB Online 中打开

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

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Andres Gustavo Ambriz Gudiel 2021-8-3

Thank you. I appreciate it . I”ll do it next time.

Wan Ji 2021-8-10

在 MATLAB Online 中打开

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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