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trapz whe x is a matrix

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Jose Costa
Jose Costa on 19 Nov 2019
Commented: dpb on 22 Nov 2019
I have a Y matrix size 2500x11 were each line corresponds to the 11 vales of curve points for trapezoidal integration.
the x values are not uniform and they vary so i have a second matrix for X size 2500x11.
I' tring to integrate using trapz (X,Y,2) but I get error "X must be a vector.".
How ca one use trapz with a matrix for x values? In octave it works.

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Accepted Answer

dpb
dpb on 19 Nov 2019
TMW only implemented variable X spacing for the full array, not by column (or row). Have to loop to do it...worthy of an enhancement request for the added functionality it would seem.
N=size(Y,1);
for i=1:N
Q(i)=trapz(X(:,i),Y(:,i));
end

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Jose Costa
Jose Costa on 22 Nov 2019
Thanks, But loops are always very slow. Prefere in this case to explicitly code the trapezoidal method and use matricial calculation.
In the 50x11 example, loop time was 0.0456 and matrix time was 8.6840e^-4
An enhancement would be good. In Octave it exists.
Jose Costa
Jose Costa on 22 Nov 2019
sorry, 2500x11.
dpb
dpb on 22 Nov 2019
MATLAB is not Octave! Converse is also true... :)
Feel free to submit the enhancement request...I'd suggest referencing this thread if do so.

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