Matrix integral over layers

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Lev Mihailov
Lev Mihailov am 17 Jul. 2020
Beantwortet: Bjorn Gustavsson am 17 Jul. 2020
Hello! I have a matrix in it the number of steps per time. Is it possible to integrate each column of the matrix layer by layer (layer sizes may differ)
MatrixHelpStep=rand(30,40);
layer=(1:5:30); % for example, I took layer 5 (but it can change)
% trying to create a loop for layers
for i=1:length(layer)-1
Imhs=trapz(MatrixHelpStep(layer(i):layer(i)+1))
end
it gives me only one value
  4 Kommentare
Walter Roberson
Walter Roberson am 17 Jul. 2020
Could you confirm that you want overlap? trapz(x(1:5,1)) uses 5 elements to form the output, but trapz(x(5:10,1)) uses 6 elements to form the output. Are you wanting 1:5, 6:10, 11:15, 16:20 and so on?
Lev Mihailov
Lev Mihailov am 17 Jul. 2020
yes, I want such overlaps

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Bjorn Gustavsson
Bjorn Gustavsson am 17 Jul. 2020
For this I would try cumtrapz - it calculates the cumulative (sp?) trapezoidal integral in the same manner as cumsum calculates the cumulative sum along an array. Doing that would give you the cumulative integrals of your matrix with the same size as your matrix. That way you can easily calculate every following integral between 2 boundaries from that one just by taking the difference between the corresponding boundary-elements. Something like this:
I = peaks(40);
I = I(1:30,:);
ciI = cumtrapz(I);
i10to17ofI = ciI(17,:) - ciI(10,:);
HTH

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