Area under curve of data points (no function) with x and y boundary

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Noa Hoogeweg 2020-10-18

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评论： Ameer Hamza 2020-10-20

Hello, how can I compute the area under a curve (see green area) of data points with a x and a y boundary? The x boundary = 70 and y=0.05. I tried trapz but I don't know how to use this with an x and an y boundary. The curve is made up of data points imported from excel:

x= xlsread(datafile, 'x-axis', 'B5:MI5');

y=xmid = xlsread(datafile, 'y-axis', 'B5:MI5');

area = trapz(x,y) %this gives the whole area under the red curve, but I only want the green area

I hope someone can help me, thanks!

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Ameer Hamza 2020-10-18

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编辑：Ameer Hamza 2020-10-18

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Something like this

mask = x > 70;
xv = x(mask);
yv = y(mask);
trapz(xv, yv-0.05); % if all the points are above x-axis then just subtracting 0.05 is enough.

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Noa Hoogeweg 2020-10-20

I modified it a bit, and I think this works better in general:

mask = x >= 70;

xv = x(mask);

yv = y(mask);

trapz(xv(yv>=0.05), yv(yv>=0.05));

Correct me if I'm wrong :)

Ameer Hamza 2020-10-20

Yes, If you only want to integrate when y is above 0.05 then it is correct.

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