Trying to find area under my plot
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I have plotted my data (two vectors of size 300x1 each) and it looks like this (see attachment):
I have tried to use trapz to get my area and get a value of around 46.
Looking at the graph, I can tell this area is wrong. Very roughly it should be around 12
So how do i get my area to equal to 12?
Thanks for any help
Answers (2)
Torsten
on 28 Nov 2022
Edited: Torsten
on 28 Nov 2022
To get the positive and negative areas separately, cut your closed curve at the two positions where it passes the x-axis and take the line connecting these two points on the x-axis to close the upper and lower curves.
n = 100;
I = linspace(0,1,n);
x = cos(2*pi*I);
y = sin(2*pi*I);
polyarea(x,y)
pi
0 Comments
John D'Errico
on 28 Nov 2022
You don't give your data. You show only a plot. So make a polyshape of it. Then compute the area.
t = linspace(0,2*pi,50);
x = cos(t);
y = sin(t);
x(end) = [];
y(end) = [];
ps = polyshape(x,y);
area(ps)
As you can see, this is just unit curcle, so the area would be pi, at least if we had more points.
plot(ps)
hold on
plot(x,y,'o')
axis equal
grid on
2 Comments
Torsten
on 29 Nov 2022
Edited: Torsten
on 29 Nov 2022
I'd cover the area of interest by a fine enough mesh of squares and count them.
I think this will be more reliable than to use polyarea to the dataset that you included.
The other alternative is to work on your data so that you extract a sequence of points that don't overlap and repeat and that represent the upper and low part of your area, respectively.
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