Area between two curves

Question

Christian Reece 2015-4-23

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https://ww2.mathworks.cn/matlabcentral/answers/213177-area-between-two-curves

回答： Star Strider 2015-4-23

I was wondering if there was a simpler/faster way of calculating the area between the two curves at each point (both of which are normailsed so the total area is 1). I am currently using a simple for loop to get the area between each set of points for the two curves, then subtracting it to get the difference i.e.

      for i = 1:length(normpeak)-1
      resN(i) = trapz(time(i:i+1),peak1(i:i+1));
      resF(i) = trapz(time(i:i+1),peak2(i:i+1));
      end
      res = resN-resF;

This works, but unfortunately it is very slow. I was reading up on the trapz function and from what I understood it calculates the total integral by performing something very similar to what i'm doing now (see image) but sums the data at the end.

Is there a way to stop trapz from performing this summing of the data, so I can speed up my code?

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Answer 1

Star Strider 2015-4-23

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在 MATLAB Online 中打开

Use the cumtrapz function to get the cumulative integral at every point.

I don’t have your data so I can’t test it, but this approach could work:

res = cumtrapz(time, peak1) - cumtrapz(time, peak2);

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Answer 2

Binbin Qi 2015-4-23

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if you can get the points of every curve, you can use polyarea function to get the area, and then diff

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Christian Reece 2015-4-23

Thanks for the answer, but this doesn't seem to work. I think I was too vague before but what I need is the difference in area at each point on the curve.

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