SPECPR Users’ Manual                                            Page 8-f43.1

F43:  Fast Fourier Transform (FFT) and Inverse FFT      Alias = fft
This routine performs a Fast Fourier Transform (FFT) on a spectrum.  The
spectrum can be any number of channels; the algorithm pads the
spectrum with zeros to a power or 2 number of channels in order to
do the FFT.  For example, if you have 931 channels, the algorithm pads the
data to 1024 channels.  The resulting FFT is NOT folded: zero frequency occurs
at channel 1 and the maximum channel, and the maximum frequency occurs in
the middle channel.
The f43 routine does not save both the real and imaginary components
at this time.  Thus the user must run f42 twice: once to save the
real component and the second time to save the imaginary component.
The inverse FFT requires both real and imaginary components.  If you
have only the real, you could use a data set of zeros for the
imaginary components (but this is not strictly valid).