Using trapz for non-linear data points
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Hello,
I have a speed vs time plot shown below.
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/152378/image.png)
I want to know how acccurate is the trapz function in MATLAB for calculating the distance travelled (i.e area under the graph). Would you suggest if there is an another means of obtaining a better approximation for the area under the graph?
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Star Strider
2015-7-22
I would use cumtrapz to give instantaneous distance traveled, for instance:
dist_nm = cumtrapz(airspeed, time_num);
I would create a time vector using datenum, subtracting the first value to create a realistic time vector in the context of your data:
time_num = datenum(time) - datenum(time(1));
Do the appropriate adjustments to the datenum calls if your ‘time’ data are not already in date number format.
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Star Strider
2015-7-22
Correct. The last value of cumtrapz is the value of the entire integral, equivalent to trapz.
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