Purpose: Computation of the spectrum by fourier-transforming
          the cross-correlation function.
          Output is: Energy, Re(FT), Im(FT), Abs(FT),
          where FT denotes the Fourier-transform (prefactor Pi^-1)
          of the cross-correlation function.

Usage : crosspec [-o -e -p -q -a -g -all -reim -re -im -sin -cos -dc -t
                    -nofs -G -ph -r -old -h ] [emin emax unit file].

Options : 
 -o FILE : The spectrum is written to file FILE.pl
           rather than to ./cspec.pl
           The string FILE may be a relative or full path-name.
 -e R Unit : the offset energy is set to R in units Unit; e.g. 0.3 ev
 -p I    : The no. of plot-points is I rather than  500
           Use "-p 2000" for final plots
 -q I    : Same as -p I
 -g      : GNUplot command lines are written to the output file.
 -a      : GNUplot is called automatically. (sets "-g").
 -all    : Re, Im and Abs parts (rather than Abs) are plotted.
           (ignored if neither -g or -a are set).
 -reim   : Real and Imaginary parts (rather than Abs) are plotted.
           (ignored if neither -g or -a are set).
 -re     : Real part (rather than Abs) is plotted.
           (ignored if neither -g or -a are set).
 -im     : Imag. part (rather than Abs) is plotted.
           (ignored if neither -g or -a are set).
 -sin    : The crosscorrelation function is multiplied with sin(pi*t/T).
 -cos    : The crosscorrelation function is multiplied with cos(pi*t/2T).
 -dc     : A DC component is subtracted from the cross-corr before FT.
 -r      : Plot the resolution rather than the spectrum
 -ph  ph : Use phase correction exp(i*ph*1.0e-6_dop*t^2)
 -t tcut : The crosscorrelation function is read only up to t=tcut
 -nofs   : No transformation to fs. Use when "time-not-fs" was set in mctdh.
 -G      : Plot gridlines (meaningfull only if -g or -a is set).
 -old    : The old output format is used.
           (Different order of colums, output times Pi.)
 -ver    : Version information about the program 
 -h      : Print this help text. 
 -?      : Print this help text. 
Following the options one may provide the arguments (separated by blank):
           Emin, Emax, Unit file
where file denotes the path of the crosscorr file.
If not enough arguments are given, the user is prompted for the missing 
arguments. Use the Unit 'no' if the propagation is run with the
keywords: 'time-not-fs','energy-not-ev'.
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