Usage: 1dfft [options] infile outfile
where infile is an AFNI *.1D file (ASCII list of numbers arranged
in columns); outfile will be a similar file, with the absolute
value of the FFT of the input columns. The length of the file
will be 1+(FFT length)/2.
Options:
-ignore sss = Skip the first 'sss' lines in the input file.
[default = no skipping]
-use uuu = Use only 'uuu' lines of the input file.
[default = use them all, Frank]
-nfft nnn = Set FFT length to 'nnn'.
[default = length of data (# of lines used)]
-tocx = Save Re and Im parts of transform in 2 columns.
-fromcx = Convert 2 column complex input into 1 column
real output.
[-fromcx will not work if the original]
[data FFT length was an odd number! :(]
-hilbert = When -fromcx is used, the inverse FFT will
do the Hilbert transform instead.
-nodetrend = Skip the detrending of the input.
Nota Bene:
* Each input time series has any quadratic trend of the
form 'a+b*t+c*t*t' removed before the FFT, where 't'
is the line number.
* The FFT length can be any positive even integer, but
the Fast Fourier Transform algorithm will be slower if
any prime factors of the FFT length are large (say > 997)
Unless you are applying this program to VERY long files,
this slowdown will probably not be appreciable.
* If the FFT length is longer than the file length, the
data is zero-padded to make up the difference.
* Do NOT call the output of this program the Power Spectrum!
That is something else entirely.
* If 'outfile' is '-' (or missing), the output appears on stdout.
++ Compile date = May 30 2023 {AFNI_23.1.07:linux_ubuntu_16_64}