Calculating an area under a curve

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Rengin
Rengin 2019-3-13
评论： Torsten 2019-3-13
% Dear users,
% Is there any way to calculate an area under a curve as in the figure?
% It would really appreciate if you can help me.
% Thanks in advance!
Area Calculation Matlab.jpg
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Rengin
Rengin 2019-3-13
Dear Torsten,
You answered my question regarding the area under the curve. You suggested me the apply the equations below:
idx = t>0.2 ;
tp = t(idx );
up = u(idx );
area = trapz(tp,up)
I wonder if the calculated area is limited by the bottom dashed line or it also includes beyond this dashed line. I don't want to include the area from origin on but from P(0.2,187).
Thanks in advance!
Torsten
Torsten 2019-3-13
The formula is gives an approximation for
integral_{t=0.2}^{t=t(end)} u(t) dt.
It seems that you want the area start at u=0.2.
Then subtract the area of the rectangle between u=0 and u=0.2 for 0.2 <= t <= t(end), i.e.
area = trapz(tp,up) - (tp(end)-0.2)*0.2

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