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 Purpose: Calculates the cross-correlation function c(t)
          c(t) = 

 Usage  : crosscorr [-f -i -o -n -r -R -O -t -nofs -el -ig                       -spf -diag -ph -M -ver -h -?]  psi_ref .

Options : 
 -f FILE : The wavefunction (density operator) 
           is read from file FILE rather than from ./psi
           The string FILE may be a relative or a full path-name.
 -o FILE : The difference is written to file FILE rather than to ./cross_XXX
           The string FILE may be a relative or a full path-name.
           If FILE=no, i.e. "-o no", no cross-file will be opened
           and the output will be directed to screen.
 -r      : Take the restart rather than the psi file as reference WF.
 -R      : Take the restart rather than the psi file as time-dep. WF.
           In general, this makes sense only when also -r is set.
 -O oper : Apply operator "oper" before evaluating the overlap.
 -t tfin : Compute the overlap only up to tfin.
 -nofs   : No transformation to fs. Use when 'time-not-fs' was set in mctdh.
 -n step : Compute the overlap only every step-th output.
 -i init : Compute the overlap using the init-th (rather than the first)
           reference WF. (-i is ignored when -r is set).
 -el nst : Compute the cross-correlation for state nst only.
 -ig     : Ignore "different bases" error-msg.
 -spf    : Print information on overlap of the two orbital sets.
           dim - trace(dover^+ * dover) for all m,s.
 -diag   : Print the absolute values of diagonal elements of the
           overlap matrix of the two orbital sets.
 -ph     : Multiply crosscorrelation with a constant phase such that C(t=0) is real.

 -M      : Matrix-elements. The reference state is taken as time-dependent.
           This requires MCTDH WFs of identical structure.
 -s s s1 : Compute the overlaps < Psi(t)_s|Psi1(t)_s1>,
           s and s1 denote the electronic states of bra- and ket-WF.
 -single i j : Compute the overlap < Psi(t_i)|Psi1(t_j)>,
           i and j denote the positions of WFs in the of bra- and ket-WF files.
 -ver    : Version information about the program 
 -h      : Print this help text. 
 -?      : Print this help text. 

 The argument psi_ref is the name of the file containing the
 (time-independent) comparison wavefunction (density  operator).

 With the aid of the option -M, crosscorr computes overlaps
 . If in addition -O is set, matrix-elements
  are calculated. Note that psi_ref is now taken as time-dependent.

-O, crosscorr can compute matrix elements . This, however, requires that 
psi_ref and psi are MCTDH-WFs with 
identical numbers of SPFs.
 If no argument is given, the user is prompted for the missing argument.
 Note: The option "-o no" directs output to screen.
 Note: If the argument ends with a slash "/", the string "psi" or "restart"
       is appended. If the argument ends with "restart", -r is set.
 Note: crosscorr can overlap two MCTDH or two ML-wavefunctions,, but not a mixture of the two types.
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