# How can I calculate trapz value based on an event counter and then plot it?

2 views (last 30 days)
Dennis on 13 Sep 2022
Commented: Dennis on 16 Sep 2022
Hey there,
the following lines of code should implement a calculation of an integral for certain events in the data.
The very first colum is the time, the second the corresponding value and the third column the event counter.
The values are saved in the integ_mtrx. It worked with cumtrapz, but i am having my problems with the trapz function.
Here the events 0 should be calculated. Events with 0 in the second colum shouldn't be calculated ( like event 1,2,3,4,..)
for every event the integral should be calculated:
for i= 0:(vzwcounter)
clear temp;
temp = Integ_MTRX(Integ_MTRX(:,3)==i,:);
B(i,1)= trapz(temp(:,1),temp(:,2));
end
Dennis on 14 Sep 2022
I attached you the Integ_MTRX and vzwcounter data.
Both images are from Integ_MTRX and show a snapshot from the data.
Based on the data I need to calculate the integral.
trapz(temp(:,1),temp(:,2)) should be skipped whenever the value in the third column, which are the values of vzwcounter, is changing for each entry. vzwcounter is just counting up events in a different function. for each event the integral should be calculated (e.g. event 175 in the second image, first column is the time (x) and second column are the values (y)).

Jan on 15 Sep 2022
As far as I understand your code was almost working. I added an if condition to skip scalar data and shifted the index for the output B by 1 because 0 is no valid index in Matlab:
B = nan(1, vzwcounter + 1);
for k = 0:vzwcounter
temp = Integ_MTRX(Integ_MTRX(:, 3) == k, :);
if size(temp, 1) > 1
B(k + 1) = trapz(temp(:, 1), temp(:, 2), 1);
end
end
Dennis on 16 Sep 2022
THANK YOU!
You solved my problem! Was quite a fight but we got it!

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