fft.txt

一个组合程序

Program FFT.FOR

This FORTRAN program calculates the fast Fourier transform of a
timeseries (real and/or complex) or the inverse Fourier transform 
of spectral components (real and/or complex).  The FFT is based 
on the algorithm given in Numerical Recipes, Cambridge University 
Press, 1994.

INPUT 

The program prompts for the name of the input and output files.  
The input data file is then read and should be in the following 
format.

card 1	descriptive header
card 2	isign 
card 3	dt  NN
card 4	format(1x,f12.5,1x,f12.5)  real part    imag part
card 5   .		.
   .	    .		.
   .	    .		.

isign = +1 for forward FFT, isign = -1 for inverse FFT
dt is the time step
NN is the number of data pairs (NN=power of 2)
if isign = +1, real part and imag part are the equally spaced 
               timeseries terms
if isign = -1, real part and imag part are the spectrum terms 
               at the Fourier frequencies

OUTPUT

The output file first echos the input data.  Then it gives time, 
f(t) real, f(t) imaginary, frequency, F(f) real, F(f)imaginary as 
format(1x,6(e11.4,1x)).  The following is a piece of the output file.

 Input file name:    data1.prn   
 Input file header:  Timeseries with 10 frequency components.                       
 number of points:         1024
 isign:                       1
 time step:          .10000E+01
 Nyquist frequency:  .50000E+00

                    fn(time)                            Fn(freq)
    time        real        imag        freq        real        imag
   .0000E+00   .1603E+00   .0000E+00   .0000E+00   .1457E-06   .0000E+00
   .1000E+01   .2390E+00   .0000E+00   .9766E-03  -.1991E+00  -.4587E+00
   .2000E+01   .3135E+00   .0000E+00   .1953E-02  -.4972E+00   .5266E-01
   .1000E+01   .2390E+00   .0000E+00   .9766E-03  -.1991E+00  -.4587E+00
   .2000E+01   .3135E+00   .0000E+00   .1953E-02  -.4972E+00   .5266E-01