Problem Calculating Mean of Function

Hello,

I have two variables with dimensions 195414 x 1, FeatureDrag and TopDrag

I am getting different results when I calculate the mean of the percent difference between the two variables. Anyone spot an issue I seem to be blind to?

Approach 1:

Drag_reduction_instant = (FeatureDrag-TopDrag)./TopDrag;
DR1 = mean(Drag_reduction_instant, "all")*100;

Approach 2:

TD_Final = mean(TopDrag, "all"); %Top Drag, mean of whole dataset
FD_Final = mean(FeatureDrag, "all"); %Feature Drag, mean of whole dataset
DR2 = (FD_Final-TD_Final)/TD_Final*100; % these two should be identical

Answer 1

[Torsten]

It's obvious that mean(x/y) does not equal mean(x)/mean(y) for arrays x and y. Test it for a simple example.

[Ben Hamilton]

Thank you for pointing that out. I guess I have never come across this before and will have to do some more reading.