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.