Calculating an area under a curve

% 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!

[Torsten]

What information about the curve so you have ? An equation ? Single data points ?

[Rengin]

I have the single data points. For each time slot (t=0,...1), I have a "u" value. It is a curve from a simulator. There is not a specific function behind it.

[Torsten]

If t and u are the arrays with the data points, you can use

idx = t>0.2;
tp = t(idx);
up = u(idx);
area = trapz(tp,up)

[KSSV]

Also have a look on polyarea.

[Rengin]

I think it works perfectly. Thank you very much!

[Rengin]

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]

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