How can I compute Trapezoidal numerical integration (Q = trapz(X,Y), while my X is a datetime-lalue vector?

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ADJE JEREMIE ALAGBE 2021-1-27

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评论： Mathieu NOE 2021-1-27

volumes.xlsx

Hi everyone, I am trying to calculate the integrale of Y vector ( some observation values) with respect to x-coordinates (datetime values) (see volumes.xlsx file). the column of Y represent volume data, taken at the times contained in X, that take place at 3 minute-intervals, for one day. How can I do that to get a result of integral that is a number, not a time-format value? For example I got sometime this:

Q = trapz(X,Y)

Q =

duration

153:03:00

but I want a result that is number, for example 10.

Any idea to help? Thanks everyone!

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Answer 1

Mathieu NOE 2021-1-27

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hello

see below , depends if integral must be done on seconds or minutes time stamps - you to choose !

 T = readtable('volumes.xlsx') ;
data = cellfun(@double,table2cell(T(:,2))); 
% extraction of minutes time vector from date vector
dd = datenum(T{:,1}); % expressed in unit "days" 
dd = dd - dd(1); % vector must start at zero
time_minutes = dd*24*60;
time_seconds = time_minutes*60;
% do the trapz integration 
Int_vol_minutes = trapz(time_minutes,data)
Int_vol_seconds = trapz(time_seconds,data)