# Area under curves with different length (trapz)

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mael thevenot on 17 Sep 2018
Answered: Fabio Freschi on 4 Dec 2019
Hi,
I'm trying to use the trapz command on MatLab R2015b.
I have 2 waves of data : y1(1x1036 double) and y2(1x9958 double) with different acquisition time, and I want to compare the area under both curves. But since the second wave have way more points I found a value much higher that did not make sense.
How can I do to tell the trapz function to take one value out of 10 for exemple? I've tried messing with the X parameter in
trapz(X, Y)
but I did not manage to make it work.
Thanks
Fabio Freschi on 4 Dec 2019
Do you know the x axis for both waves?

Fabio Freschi on 4 Dec 2019
If you have the x axes for both waves, it is pretty easy to use trapz:
N1 = 1036;
N2 = 9958;
% wave 1
x1 = linspace(0,2*pi,N1);
y1 = sin(x1);;
% wave 2
x2 = linspace(0,2*pi,N2);
y2 = sin(x2);
% integrals
I1 = trapz(x1,y1)
I2 = trapz(x2,y2)
Both values are very close to 0, in line with the theory