How do I calculate the area under a curve?

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SS 2020년 5월 14일
댓글: Image Analyst 2020년 5월 16일
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.

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Image Analyst
Image Analyst 2020년 5월 14일
편집: Image Analyst 2020년 5월 14일
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.
  댓글 수: 2
SS 2020년 5월 16일
편집: SS 2020년 5월 16일
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
Image Analyst 2020년 5월 16일
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???

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