Getting area of selected area plot?

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IJ
IJ 2016-4-25
评论： Star Strider 2016-4-26
Is it possible to calculate the area selected with the area plot (example attached)?
Working with area plots allows to visually confirm how accurate my selection of points are, but I don't know how to get the filled area. I know that trapz is used for data under curve calculations, but my values are negative, plus I cannot see the exact data calculated with trapz, so I cannot confirm if I use it as I think I am.
---edit
Does this do the job?
trapz(selectedArea.YData, selectedArea.YData)

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回答（1 个）

Star Strider
Star Strider 2016-4-25
That won’t, but this might:
sel_area = trapz(selectedArea.XData, selectedArea.YData);
assuming of course that ‘selectedArea.XData’ exists.
  2 个评论
IJ
IJ 2016-4-26
XData and YData are properties of area.
Great, thanks! Do you know how I can plot area from trapz-calculated data? So, the other way around.
For example, if I wanted to confirm whether I calculated the correct selection. If I use the same y values and plot with area(), will it always reflect what trapz() calculated?
Star Strider
Star Strider 2016-4-26
My pleasure.
I’m not certain what you’re asking. The area plotted with area should reflect what trapz calculated, however I have no idea how you would verify that. (One possibility might be the polyarea function.) Also, see if the related cumtrapz function will do what you want.

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