FOURIER is the jSpectral module of jLab.

 FOURIER  Returns the Fourier frequencies for a given length time series.
 
    F=FOURIER(M) returns the one-sided (or positive) Fourier frequencies 
    for a time series of length M.   
 
    F is a radian or angular frequency so that the Nyquist is at PI.
 
    F=FOURIER(M,'two') instead returns the two-sided Fourier frequencies.
    The default behavior is equivalent to F=FOURIER(M,'one').
 
    F=FOURIER(DT,M) uses sample rate DT in calculating the frequencies, so
    that the Nyquist will be at PI/DT.
  
    Note that the highest resolved frequency, MAX(F), differs for even or
    odd M.  For even M, it is the Nyquist PI/DT, but for odd M the Nyquist
    is not resolved and the highest resolved frequency is (M-1)/M * PI/DT.
 
    For the one-sided option, F has length FLOOR(M/2)+1, or M/2+1 for even 
    M, and (M+1)/2 for odd M.  For the two-sided option, F has length M.
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    Array input
 
    F=FOURIER(M) also works if M an array instead of a scalar.  In this
    case, F is a cell array with LENGTH(M) elements.
 
    F=FOURIER(DT,M) with M being an array works provided DT is either a 
    scalar or an array of the same length as M.   
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    See also CENTEREDTIMES.
 
    Usage: f=fourier(M);
           f=fourier(dt,M);
           f=fourier(dt,M,'two');
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    This is part of JLAB --- type 'help jlab' for more information
    (C) 2011--2019 J.M. Lilly --- type 'help jlab_license' for details