COMPUTE FFT

        [SIC\]COMPUTE OutVar FFT+|FFT- InVar [REAL]

    FFT+ performs Direct Fast Fourier Transform, while FFT- performs Inverse
    Fast Fourier Transform.

    Command accepts REAL or COMPLEX variables. OutVar is a  2-D  array  with
    second  dimension  equals 2, storing respectively the Real and Imaginary
    part of the (complex) output Fourier transform.  By  default,  InVar  is
    like OutVar, but if parameter REAL is specified InVar is a 1-D array.