[Tutor] fourier transform
Christian Meesters
meesters at uni-mainz.de
Sat Jul 30 14:05:40 CEST 2005
Jeff Peery wrote:
>
> Hello, I have a signal that I want to do a fourier transform on. I
> tried using FFT.fft(data).real but I don't understand the output.
> what is output from this function, and why doesn't it require
> amplitude and time as inputs?
Hi Jeff,
As Danny wrote, your input are real numbers and your output will be
complex numbers. I don't want to point you to the numarray
documentation once more, but you might to check out this:
http://mathworld.wolfram.com/FourierSeries.html as for why you get
complex numbers back. (To get only the real value part try real_fft()
in numarrayl.)
In general in numerical computation your input is simply a series of
real numbers - of equal spacing in the dimension you want to consider.
Which dimension you choose (amplitudes and time/phase or amplitudes and
spacial frequencies and so on) is up to you. It depends on your
physical or mathematical question. IMHO the best introduction you can
get on Fourier Transforms & programming can be found in Numerical
Recipies (here the "Numerical Recipies in C"-link
http://www.library.cornell.edu/nr/bookcpdf.html - check chapter 12).
Have fun with FFTs!
Cheers
Christian
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