MATLAB: How to calculate partial area-under-the-curve

plottrapz

Hi, I'm trying to find the area under the curve (ABC) for a part of a graph. I use the "trapz" function, but this function calculates the ABC for an entire area below the selected part of the graph. Any tips on how I can calculate only part of it (not the whole part up to the x axis)? Please see the figure. Interested are to be calculate is in red.

Thanks, Jacqueline

Best Answer

Use trapz twice, once to integrate (A, B, C), and again to integrate (A, C).

Then subtract the (A, C) result from the (A, B, C) result.

It would definitely help to have the data, preferably as a .mat file.

Related Solutions

MATLAB: Error: “Dimension argument must be a positive integer scalar within indexing range” using trapz

hello Jacqueline

with the given limits xi=5.67; xf=14.20; , idl contains only one valid x value , so trapz will throw an error, because it needs at least vector of 2 scalars (and you give only one value)

I guessed that you needed to include the 14.2002 value in your x vector , so simply make the second limit a bit higher : xf=14.21;

and then it's fine, you can do the trapz computation

results :

area_selected = 43.8377

area_total = 123.3377

MATLAB: Area fill between minimum and maximum axis limit

You need to create a closed area for patch, that proceeds clockwise (or anticlockwise).

The Code —

figure
patch([data_1; flipud(data_2)], [idx; flipud(idx)], 'r')
ylabel('Index')

The Plot —

Best Answer

Related Solutions

MATLAB: Error: “Dimension argument must be a positive integer scalar within indexing range” using trapz

MATLAB: Area fill between minimum and maximum axis limit

Related Question