Complexity order of fft in matlab

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Ziwen Gu 2023-10-27

评论： Ziwen Gu 2023-10-28

Hello everyone, I want to check the complecity order of fft is O(N*log(N) in matlab, so I ran the code below:

The expected ratio is 1 : 2.8 : 7.8 , which is far away from code's result.

Can anyone explain what is wrong?

David Goodmanson 2023-10-28

编辑：David Goodmanson 2023-10-28

Hello ZG,

the elapsed times from toc will not totally agree with O(nlog(n)), but surely that expected ratio is not as extreme as 1 : 2.8 : 7.8 :

n = [1 2 4]*1e5;
n.*log(n)/(n(1)*log(n(1)))
ans =  1.0000    2.1204    4.4816

Ziwen Gu 2023-10-28

Uhhhhhhh, thanks a lot, goodmanson, may you have a plesant day.

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