How do I calculate the area under a curve?

Question

SS 2020-5-14

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/525464-how-do-i-calculate-the-area-under-a-curve

评论： Image Analyst 2020-5-16

area.jpg

I have a reading curve from some experimental observations. I want to calculate the area under the curve - between customized X and Y values. I want it in between X=[-0.9,+0.9] and Y=[0.3,0.45]. How can I do it? I am attaching the figure for reference.

0 个评论
显示 -2更早的评论隐藏 -2更早的评论

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Image Analyst 2020-5-14

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/525464-how-do-i-calculate-the-area-under-a-curve#answer_432466

编辑：Image Analyst 2020-5-14

在 MATLAB Online 中打开

Did you try

indexes = X >= -0.9 & X <= 0.9;
area = trapz(X(indexes), Y(indexes))

But what do you mean with those Y limits? That would just be a rectangular box under the curve.

2 个评论
显示无隐藏无

SS 2020-5-16

编辑：SS 2020-5-16

Thanks for your reply. I have enclosed that graph just an example. My experimental system gives some reading curve which can also be imported to MATLAB (as a fig file). I don't have specific X and Y coordinates (data points).

How is it possible to calculate the area under the curve of an already existing figure?

Image Analyst 2020-5-16

Yes, but you'd have to somehow extract the x and y out of the figure. I never do that but I know it's possible. How did the figure get made in the first place? Why do you not have the actual coordinates in your script, function, or in a mat file???

请先登录，再进行评论。