:orphan: .. _ahelp_1dfft: ***** 1dfft ***** .. contents:: :local: | .. code-block:: none 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 = Oct 13 2022 {AFNI_22.3.03:linux_ubuntu_16_64}