This program takes an input file with time-data and calculates the
powerspectrum/fourier transform of the autocorrelation function.
The input file must only have lines of the form

<integer> <dummy 1> <dummy 2> <dummy 3> <data 1> <data 2> <data 3>

where the first four entries are ignored and the autocorrelation/
fourier-transform is performed on the last 3 entries of a line.
The name of the input file as well as other needed quantities
are queried by the program interactively.

The output file will contain the power-spectrum up to a maximum frequency.
The format of this file is:

<frequency> <value1> <value2> <value3> <value4> <value5>

<frequency> is the frequency in wave numbers.
<value1>    is the plain power spectrum of the input data (normalized to
            unity in the output frequency range.
<value2>    is the power spectrum with a prefactor of 
            \omega ( 1 - \exp(-\beta \hbar \omega) )
            corresponding to the classical/Gordon limit.
<value3>    is the power spectrum with a prefactor of
            \omega \tanh(\beta \hbar \omega/2)
            corresponding to the Kubo correction
<value4>    is the power spectrum with a prefactor of
            \omega \beta \hbar \omega
            corresponding to the high temperature / harmonic limit
            Note: this is the recommended correction factor.
<value5>    is the power spectrum with a prefactor of
            \omega ( 1 - \exp(-\beta \hbar \omega) ) *
                                             \exp(\beta \hbar \omega /2)
            corresponding to Schofield's correction
All spectra with their corresponding prefactor are separately normalized
in the output range to sum up to unity.

Note: the index of refraction of the medium is set to unity.

Version 30.4.2002 - H. Forbert   harald.forbert@theochem.ruhr-uni-bochum.de