





SPECPR Users' Manual                                            Page 8-f43.1


_F_4_3:  _F_a_s_t _F_o_u_r_i_e_r _T_r_a_n_s_f_o_r_m (_F_F_T) _a_n_d _I_n_v_e_r_s_e _F_F_T      _A_l_i_a_s = _f_f_t

     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 chan-
nels.  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 com-
ponent 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 com-
ponents (but this is not strictly valid).





































