How to calculate the area of the green shaded region in MATLAB

2015 1 30
3 个回答
更新时间：2015 2 2
11 次查看（30 天）

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Hello,
Could you please guide me how to calculate the area of the green shaded region (between blue and red curve) of the attached figure in MATLAB. Please see the attached pic named "how to calculate area".
Blue line has the value of 1 p.u and is a straight horizontal line.
Thanks

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回答（3 个）

Image Analyst
Image Analyst 2015-1-30

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Exactly what form is your data in? An image file? An equation? A list of (x,y) coordinates in a MATLAB variable? Do you have those 3 (x,y) pairs you show in the annotation? Exactly what are you starting with? If you have the three points, can't you just use the formula for a triangle: area = (1/2)*base*height???

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Farhan
Farhan 2015-1-30
Hello,
Please find that more zoomed in view. It will show that this shape is not a triangle. the quantity i am plotting is the voltage of a bus in my power system. My data is in the form of array in workspace 9911x1 is the size.I can get the (x,y) pairs of the three points after plotting my array. How to calculate the area of this kind of shape? Please help!
Image Analyst
Image Analyst 2015-1-30
Where did you post the "more zoomed in view"? Can't you just use quad()? Or even polyarea()???
Farhan
Farhan 2015-2-2
I have attached the zoomed in view in my previous message. File name "How to calculate area_zoomed"
I have tried using quad, for that it needs a function e.g. q = quad(fun,a,b)
i have a plot in the form of array in MATLAB workspace, but how to convert this array into a function?? So that it can be used to calculate area using quad?
Also please find the attached code and data file that is needed for code.

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Farhan
Farhan 2015-2-2

0 个投票

I have attached the zoomed in view in my previous message. File name "How to calculate area_zoomed"
I have tried using quad, for that it needs a function e.g. q = quad(fun,a,b)
i have a plot in the form of array in MATLAB workspace, but how to convert this array into a function?? So that it can be used to calculate area using quad?
Niels
Niels 2015-2-2
编辑：Niels 2015-2-2

0 个投票

Is it not possible to simply calculate the difference between your y-values and the straight line, take the mean of every 2 neigboring y-values, then multiply those values by your x-spacing and then sum all the values between x = 2166 and x = 5590? ie.
spc = 1; % spacing of x-values
x = 1:spc:20; % full x-range
x_min = 5; % lower boundary of interest
x_max = 12; % upper boundary of interest
y = 30-0.5*x + rand(1,numel(x)); % y-values for full x-range
y_ref = 30; % reference value for y
y_means = mean([y(1:end-1); y(2:end)],1) - y_ref;
y_range = y_means(x(x==x_min):x(x==x_max-1));
y_int = sum(y_range*spc);
Or more simple:
y_int = trapz(x_min:x_max,y(x_min:x_max));

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Farhan
Farhan
2015-1-30

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Niels
Niels
2015-2-2

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