fft function returns NaN from non-NaN input

Hello, I have a one dimension MATLAB vector as fft input. The plot of the vector looks like this:

Zoom it in:

I used isnan() function checked that there is no NaN in this vector. I thought this vector is totally legal to be used in MATLAB fft function.

What is wired is that when I put this vector into the function, all the returns are NaN.

If you want to try out the vector yourself, I have attached it. just load('fmu_q.mat'), and fft(fmu_q). You will see everything is NaN.

Could anyone shed some light on what happened?

Answer 1

[David Goodmanson]

Hi Yuwei, you did check for NaNs but not for any values that equal +-infinity, and there are three of them:

>> find(isinf(fmu_q))

ans = 2959        2960        2961

[Yuwei Zhu]

Thanks! That is the problem.