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Area between two curves

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Christian Reece
Christian Reece on 23 Apr 2015
Answered: Star Strider on 23 Apr 2015
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));
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?

Accepted Answer

Star Strider
Star Strider on 23 Apr 2015
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);

More Answers (1)

Binbin Qi
Binbin Qi on 23 Apr 2015
if you can get the points of every curve, you can use polyarea function to get the area, and then diff
  1 Comment
Christian Reece
Christian Reece on 23 Apr 2015
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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