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.

  -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  7 2021 {AFNI_21.1.06:linux_ubuntu_16_64}